04-Network Connectivity

HomeSupportResource CenterH3C Access Points Cloud Mode Configuration Guides(E2442 R2442)-6W10004-Network Connectivity
18-IPv6 basics configuration
Title Size Download
18-IPv6 basics configuration 355.33 KB

Contents

Configuring basic IPv6 settings· 1

About IPv6· 1

IPv6 features· 1

IPv6 addresses· 2

IPv6 path MTU discovery· 4

IPv6 transition technologies· 5

Protocols and standards· 6

IPv6 basics tasks at a glance· 6

Configuring an IPv6 global unicast address· 7

About IPv6 global unicast address· 7

Generating an EUI-64 IPv6 address· 7

Manually assigning an IPv6 global unicast address· 7

Stateless address autoconfiguration· 8

Configuring prefix-specific address autoconfiguration· 9

Configuring an IPv6 link-local address· 9

About IPv6 link-local address· 9

Restrictions and guidelines· 10

Configuring automatic generation of an IPv6 link-local address for an interface· 10

Manually assigning an IPv6 link-local address to an interface· 10

Configuring an IPv6 anycast address· 11

Configuring path MTU discovery· 11

Setting the interface MTU· 11

Setting a static path MTU for an IPv6 address· 11

Setting the aging time for dynamic path MTUs· 12

Controlling sending ICMPv6 messages· 12

Configuring the rate limit for ICMPv6 error messages· 12

Enabling replying to multicast echo requests· 12

Enabling sending ICMPv6 destination unreachable messages· 13

Enabling sending ICMPv6 time exceeded messages· 13

Enabling sending ICMPv6 redirect messages· 14

Specifying the source address for ICMPv6 packets· 14

Enabling discarding IPv6 packets that contain extension headers· 15

Display and maintenance commands for IPv6 basics· 15

Basic IPv6 settings configuration examples· 16

Example: Configuring basic IPv6 settings· 16

Configuring IPv6 neighbor discovery· 21

About IPv6 neighbor discovery· 21

ICMPv6 messages used by IPv6 neighbor discovery· 21

Address resolution· 21

Neighbor reachability detection· 22

Duplicate address detection· 22

Router/prefix discovery and stateless address autoconfiguration· 23

Redirection· 23

Protocols and standards· 23

IPv6 neighbor discovery tasks at a glance· 23

Configuring a static neighbor entry· 24

Setting the dynamic neighbor learning limit on an interface· 24

Setting the aging timer for ND entries in stale state· 25

Minimizing link-local ND entries· 25

Setting the hop limit 25

Configuring RA message sending and parameters· 26

About RA message parameters· 26

Restrictions and guidelines· 26

Enabling the sending of RA messages· 27

Configuring parameters for RA messages· 27

Specifying DNS server information in RA messages· 28

Specifying DNS suffix information in RA messages· 29

Suppressing advertising DNS information in RA messages· 30

Enabling advertising invalid delegated prefixes· 30

Setting the maximum number of attempts to send an NS message for DAD·· 31

Enabling ND proxy· 31

About ND proxy· 31

Enabling common ND proxy· 32

Enabling local ND proxy· 33

Display and maintenance commands for IPv6 ND·· 33

 


Configuring basic IPv6 settings

About IPv6

IPv6, also called IP next generation (IPng), was designed by the IETF as the successor to IPv4. One significant difference between IPv6 and IPv4 is that IPv6 increases the IP address size from 32 bits to 128 bits.

The term "router" in this document refers to OASIS APs.

IPv6 features

Simplified header format

IPv6 removes several IPv4 header fields or moves them to the IPv6 extension headers to reduce the length of the basic IPv6 packet header. The basic IPv6 packet header has a fixed length of 40 bytes to simplify IPv6 packet handling and improve forwarding efficiency. Although the IPv6 address size is four times the IPv4 address size, the basic IPv6 packet header size is only twice the size of the option-less IPv4 packet header.

Figure 1 IPv4 packet header format and basic IPv6 packet header format

Larger address space

IPv6 can provide 3.4 x 1038 addresses to meet the requirements of hierarchical address assignment for both public and private networks.

Hierarchical address structure

IPv6 uses a hierarchical address structure to speed up route lookup and reduce the IPv6 routing table size through route aggregation.

Address autoconfiguration

To simplify host configuration, IPv6 supports stateful and stateless address autoconfiguration.

·     Stateful address autoconfiguration enables a host to acquire an IPv6 address and other configuration information from a server (for example, a DHCPv6 server). For more information about DHCPv6 server, see "Configuring the DHCPv6 server."

·     Stateless address autoconfiguration enables a host to automatically generate an IPv6 address and other configuration information by using its link-layer address and the prefix information advertised by a router.

To communicate with other hosts on the same link, a host automatically generates a link-local address based on its link-layer address and the link-local address prefix (FE80::/10).

Built-in security

IPv6 defines extension headers to support IPsec. IPsec provides end-to-end security and enhances interoperability among different IPv6 applications.

QoS support

The Flow Label field in the IPv6 header allows the device to label the packets of a specific flow for special handling.

Enhanced neighbor discovery mechanism

The IPv6 neighbor discovery protocol uses a group of ICMPv6 messages to manage information exchange among neighboring nodes on the same link. The group of ICMPv6 messages replaces ARP messages, ICMPv4 router discovery messages, and ICMPv4 redirect messages and provides a series of other functions.

Flexible extension headers

IPv6 eliminates the Options field in the header and introduces optional extension headers to provide scalability and improve efficiency. The Options field in the IPv4 packet header contains a maximum of 40 bytes, whereas the IPv6 extension headers are restricted to the maximum size of IPv6 packets.

IPv6 addresses

IPv6 address format

An IPv6 address is represented as a set of 16-bit hexadecimals separated by colons (:). An IPv6 address is divided into eight groups, and each 16-bit group is represented by four hexadecimal numbers, for example, 2001:0000:130F:0000:0000:09C0:876A:130B.

To simplify the representation of IPv6 addresses, you can handle zeros in IPv6 addresses by using the following methods:

·     The leading zeros in each group can be removed. For example, the above address can be represented in a shorter format as 2001:0:130F:0:0:9C0:876A:130B.

·     If an IPv6 address contains one or more consecutive groups of zeros, they can be replaced by a double colon (::). For example, the above address can be represented in the shortest format as 2001:0:130F::9C0:876A:130B.

 

IMPORTANT

IMPORTANT:

A double colon can appear once or not at all in an IPv6 address. This limit allows the device to determine how many zeros the double colon represents and correctly convert it to zeros to restore a 128-bit IPv6 address.

An IPv6 address consists of an address prefix and an interface ID, which are equivalent to the network ID and the host ID of an IPv4 address.

An IPv6 address prefix is written in IPv6-address/prefix-length notation. The prefix-length is a decimal number indicating how many leftmost bits of the IPv6 address are in the address prefix.

IPv6 address types

IPv6 addresses include the following types:

·     Unicast address—An identifier for a single interface, similar to an IPv4 unicast address. A packet sent to a unicast address is delivered to the interface identified by that address.

·     Multicast address—An identifier for a set of interfaces (typically belonging to different nodes), similar to an IPv4 multicast address. A packet sent to a multicast address is delivered to all interfaces identified by that address.

Broadcast addresses are replaced by multicast addresses in IPv6.

·     Anycast address—An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to the nearest interface among the interfaces identified by that address. The nearest interface is chosen according to the routing protocol's measure of distance.

The type of an IPv6 address is designated by the first several bits, called the format prefix.

Table 1 Mappings between address types and format prefixes

Type

Format prefix (binary)

IPv6 prefix ID

Unicast address

Unspecified address

00...0 (128 bits)

::/128

Loopback address

00...1 (128 bits)

::1/128

Link-local address

1111111010

FE80::/10

Global unicast address

Other forms

N/A

Multicast address

11111111

FF00::/8

Anycast address

Anycast addresses use the unicast address space and have the identical structure of unicast addresses.

Unicast addresses

Unicast addresses include global unicast addresses, link-local unicast addresses, the loopback address, and the unspecified address.

·     Global unicast addresses—Equivalent to public IPv4 addresses, global unicast addresses are provided for Internet service providers. This type of address allows for prefix aggregation to restrict the number of global routing entries.

·     Link-local addresses—Used for communication among link-local nodes for neighbor discovery and stateless autoconfiguration. Packets with link-local source or destination addresses are not forwarded to other links.

·     A loopback address—0:0:0:0:0:0:0:1 (or ::1). It has the same function as the loopback address in IPv4. It cannot be assigned to any physical interface. A node uses this address to send an IPv6 packet to itself.

·     An unspecified address—0:0:0:0:0:0:0:0 (or ::). It cannot be assigned to any node. Before acquiring a valid IPv6 address, a node fills this address in the source address field of IPv6 packets. The unspecified address cannot be used as a destination IPv6 address.

Multicast addresses

IPv6 multicast addresses listed in Table 2 are reserved for special purposes.

Table 2 Reserved IPv6 multicast addresses

Address

Application

FF01::1

Node-local scope all-nodes multicast address.

FF02::1

Link-local scope all-nodes multicast address.

FF01::2

Node-local scope all-routers multicast address.

FF02::2

Link-local scope all-routers multicast address.

Multicast addresses also include solicited-node addresses. A node uses a solicited-node multicast address to acquire the link-layer address of a neighboring node on the same link and to detect duplicate addresses. Each IPv6 unicast or anycast address has a corresponding solicited-node address. The format of a solicited-node multicast address is FF02:0:0:0:0:1:FFXX:XXXX. FF02:0:0:0:0:1:FF is fixed and consists of 104 bits, and XX:XXXX is the last 24 bits of an IPv6 unicast address or anycast address.

EUI-64 address-based interface identifiers

An interface identifier is 64 bits long and uniquely identifies an interface on a link.

On an IEEE 802 interface (such as a VLAN interface), the interface identifier is derived from the link-layer address (typically a MAC address) of the interface. The MAC address is 48 bits long.

To obtain an EUI-64 address-based interface identifier, follow these steps:

1.     Insert the 16-bit binary number 1111111111111110 (hexadecimal value of FFFE) behind the 24th high-order bit of the MAC address.

2.     Invert the universal/local (U/L) bit (the seventh high-order bit). This operation makes the interface identifier have the same local or global significance as the MAC address.

Figure 2 Converting a MAC address into an EUI-64 address-based interface identifier

On a tunnel interface, the lower 32 bits of the EUI-64 address-based interface identifier are the source IPv4 address of the tunnel interface. The higher 32 bits of the EUI-64 address-based interface identifier of an ISATAP tunnel interface are 0000:5EFE, whereas those of other tunnel interfaces are all zeros.

On an interface of another type (such as a serial interface) the EUI-64 address-based interface identifier is generated randomly by the device.

IPv6 path MTU discovery

The links that a packet passes from a source to a destination can have different MTUs, among which the minimum MTU is the path MTU. If a packet exceeds the path MTU, the source end fragments the packet to reduce the processing pressure on intermediate devices and to use network resources effectively.

A source end uses path MTU discovery to find the path MTU to a destination, as shown in Figure 3.

1.     The source host sends a packet no larger than its MTU to the destination host.

2.     If the MTU of an intermediate device's output interface is smaller than the packet, the device performs the following operations:

¡     Discards the packet.

¡     Returns an ICMPv6 error message containing the interface MTU to the source host.

3.     Upon receiving the ICMPv6 error message, the source host performs the following operations:

¡     Uses the returned MTU to limit the packet size.

¡     Performs fragmentation.

¡     Sends the fragments to the destination host.

4.     Step 2 and step 3 are repeated until the destination host receives the packet. In this way, the source host finds the minimum MTU of all links in the path to the destination host.

Figure 3 Path MTU discovery process

IPv6 transition technologies

IPv6 transition technologies enable communication between IPv4 and IPv6 networks.

Dual stack

Dual stack is the most direct transition approach. A network node that supports both IPv4 and IPv6 is a dual-stack node. A dual-stack node configured with an IPv4 address and an IPv6 address can forward both IPv4 and IPv6 packets. An application that supports both IPv4 and IPv6 prefers IPv6 at the network layer.

Dual stack is suitable for communication between IPv4 nodes or between IPv6 nodes. It is the basis of all transition technologies. However, it does not solve the IPv4 address depletion issue because each dual-stack node must have a globally unique IPv4 address.

Tunneling

Tunneling uses one network protocol to encapsulate the packets of another network protocol and transfers them over the network.

AFT

AFT translates an IP address of one address family into an IP address of the other address family, enabling an IPv4 network and an IPv6 network to communicate with each other. Configured on the edge devices of the IPv4 and IPv6 networks, AFT is transparent to users and does not require configuration changes on IPv4 hosts and IPv6 hosts.

6PE

6PE enables communication between isolated IPv6 networks over an IPv4 backbone network.

6PE adds labels to the IPv6 routing information about customer networks and advertises the information into the IPv4 backbone network over internal Border Gateway Protocol (IBGP) sessions. IPv6 packets are labeled and forwarded over tunnels on the backbone network. The tunnels can be GRE tunnels.

Figure 4 Network diagram

6PE is a highly efficient solution. When an ISP wants to utilize the existing IPv4/MPLS network to provide IPv6 traffic switching, it only needs to upgrade the PE routers. In addition, the operation risk of 6PE is very low.

Protocols and standards

·     RFC 1881, IPv6 Address Allocation Management

·     RFC 1887, An Architecture for IPv6 Unicast Address Allocation

·     RFC 1981, Path MTU Discovery for IP version 6

·     RFC 2375, IPv6 Multicast Address Assignments

·     RFC 2460, Internet Protocol, Version 6 (IPv6) Specification

·     RFC 2464, Transmission of IPv6 Packets over Ethernet Networks

·     RFC 2526, Reserved IPv6 Subnet Anycast Addresses

·     RFC 3307, Allocation Guidelines for IPv6 Multicast Addresses

·     RFC 4191, Default Router Preferences and More-Specific Routes

·     RFC 4291, IP Version 6 Addressing Architecture

·     RFC 4443, Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification

·     RFC 4862, IPv6 Stateless Address Autoconfiguration

IPv6 basics tasks at a glance

To configure basic IPv6 settings, perform the following tasks:

1.     Configuring an IPv6 address

Choose the following tasks as needed:

¡     Configuring an IPv6 global unicast address

¡     Configuring an IPv6 link-local address

¡     Configuring an IPv6 anycast address

2.     (Optional.) Configuring path MTU discovery

¡     Setting the interface MTU

¡     Setting a static path MTU for an IPv6 address

¡     Setting the aging time for dynamic path MTUs

3.     (Optional.) Controlling sending ICMPv6 messages

¡     Configuring the rate limit for ICMPv6 error messages

¡     Enabling replying to multicast echo requests

¡     Enabling sending ICMPv6 destination unreachable messages

¡     Enabling sending ICMPv6 time exceeded messages

¡     Enabling sending ICMPv6 redirect messages

¡     Specifying the source address for ICMPv6 packets

4.     (Optional.) Enabling discarding IPv6 packets that contain extension headers

Configuring an IPv6 global unicast address

About IPv6 global unicast address

Use one of the following methods to configure an IPv6 global unicast address for an interface:

·     EUI-64 IPv6 address—The IPv6 address prefix of the interface is manually configured, and the interface ID is generated automatically by the interface.

·     Manual configuration—The IPv6 global unicast address is manually configured.

·     Stateless address autoconfiguration—The IPv6 global unicast address is generated automatically based on the address prefix information contained in the RA message.

·     Prefix-specific address autoconfiguration—The IPv6 global unicast address is generated automatically based on the prefix specified by its ID. The prefix can be manually configured or obtained through DHCPv6.

You can configure multiple IPv6 global unicast addresses on an interface.

Manually configured global unicast addresses (including EUI-64 IPv6 addresses) take precedence over automatically generated ones. If you manually configure a global unicast address with the same address prefix as an existing global unicast address on an interface, the manually configured one takes effect. However, it does not overwrite the automatically generated address. If you delete the manually configured global unicast address, the device uses the automatically generated one.

Generating an EUI-64 IPv6 address

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Configure an EUI-64 IPv6 address on the interface.

ipv6 address { ipv6-address prefix-length | ipv6-address/prefix-length } eui-64

By default, no EUI-64 IPv6 address is configured on an interface.

Manually assigning an IPv6 global unicast address

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Assign an IPv6 global unicast address to the interface.

ipv6 address { ipv6-address prefix-length | ipv6-address/prefix-length }

By default, no IPv6 global unicast address is configured on an interface.

Stateless address autoconfiguration

About this task

Stateless address autoconfiguration enables an interface to automatically generate an IPv6 global unicast address by using the address prefix in the received RA message and the interface ID. On an IEEE 802 interface (such as an Ethernet interface or a VLAN interface), the interface ID is generated based on the interface's MAC address and is globally unique. An attacker can exploit this rule to identify the sending device easily.

To fix the vulnerability, you can configure the temporary address feature. With this feature, an IEEE 802 interface generates the following addresses:

·     Public IPv6 address—Includes the address prefix in the RA message and a fixed interface ID generated based on the MAC address of the interface.

·     Temporary IPv6 address—Includes the address prefix in the RA message and a random interface ID generated through MD5.

You can also configure the interface to preferentially use the temporary IPv6 address as the source address of sent packets. When the valid lifetime of the temporary IPv6 address expires, the interface deletes the address and generates a new one. This feature enables the system to send packets with different source addresses through the same interface. If the temporary IPv6 address cannot be used because of a DAD conflict, the public IPv6 address is used.

The preferred lifetime and valid lifetime for a temporary IPv6 address are determined as follows:

·     The preferred lifetime of a temporary IPv6 address takes the smaller of the following values:

¡     The preferred lifetime of the address prefix in the RA message.

¡     The preferred lifetime configured for temporary IPv6 addresses minus DESYNC_FACTOR (a random number in the range of 0 to 600 seconds).

·     The valid lifetime of a temporary IPv6 address takes the smaller of the following values:

¡     The valid lifetime of the address prefix.

¡     The valid lifetime configured for temporary IPv6 addresses.

Restrictions and guidelines

If the IPv6 prefix in the RA message is not 64 bits long, stateless address autoconfiguration fails to generate an IPv6 global unicast address.

To generate a temporary address, an interface must be enabled with stateless address autoconfiguration. Temporary IPv6 addresses do not overwrite public IPv6 addresses, so an interface can have multiple IPv6 addresses with the same address prefix but different interface IDs.

If an interface fails to generate a public IPv6 address because of a prefix conflict or other reasons, it does not generate any temporary IPv6 address.

Executing the undo ipv6 address auto command on an interface deletes all IPv6 global unicast addresses and link-local addresses that are automatically generated on the interface.

Enabling stateless address autoconfiguration

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable stateless address autoconfiguration on an interface, so that the interface can automatically generate a global unicast address.

ipv6 address auto

By default, the stateless address autoconfiguration feature is disabled on an interface.

Configuring the temporary address feature and preferentially using the temporary IPv6 address as the source address of outgoing packets

1.     Enter system view.

system-view

2.     Enable the temporary IPv6 address feature.

ipv6 temporary-address [ valid-lifetime preferred-lifetime ]

By default, the temporary IPv6 address feature is disabled.

3.     Enable the system to preferentially use the temporary IPv6 address as the source address of the outgoing packets.

ipv6 prefer temporary-address

By default, the system does not preferentially use the temporary IPv6 address as the source address of the outgoing packets.

Configuring prefix-specific address autoconfiguration

1.     Enter system view.

system-view

2.     Configure an IPv6 prefix.

Choose one option as needed:

¡     Configure a static IPv6 prefix.

ipv6 prefix prefix-number ipv6-prefix/prefix-length

By default, no static IPv6 prefixes exist.

¡     Use DHCPv6 to obtain a dynamic IPv6 prefix.

For more information about IPv6 prefix acquisition, see "Configuring the DHCPv6 client."

3.     Enter interface view.

interface interface-type interface-number

4.     (Optional.) Enable advertising invalid delegated prefixes.

ipv6 nd ra invalid-delegated-prefix advertise enable

By default, advertising invalid delegated prefixes is disabled.

Perform this step if the device acts a DHCPv6 client to obtain IPv6 prefixes from the DHCPv6 server. For more information abut advertising invalid delegated prefixes, see "Enabling advertising invalid delegated prefixes."

5.     Specify an IPv6 prefix for an interface to automatically generate an IPv6 global unicast address and advertise the prefix.

ipv6 address prefix-number sub-prefix/prefix-length

By default, no IPv6 prefix is specified for the interface to automatically generate an IPv6 global unicast address.

Configuring an IPv6 link-local address

About IPv6 link-local address

Configure IPv6 link-local addresses using one of the following methods:

·     Automatic generation—The device automatically generates a link-local address for an interface according to the link-local address prefix (FE80::/10) and the link-layer address of the interface.

·     Manual assignment—Manually configure an IPv6 link-local address for an interface.

Restrictions and guidelines

After you configure an IPv6 global unicast address for an interface, the interface automatically generates a link-local address. This link-local address is the same as the one generated by using the ipv6 address auto link-local command. If a link-local address is manually assigned to an interface, this manual assigned link-local address takes effect. If the manually assigned link-local address is deleted, the automatically generated link-local address takes effect.

Using the undo ipv6 address auto link-local command on an interface deletes only the link-local address generated by the ipv6 address auto link-local command. If the interface has an IPv6 global unicast address, it still has a link-local address. If the interface has no IPv6 global unicast address, it has no link-local address.

An interface can have only one link-local address. As a best practice, use the automatic generation method to avoid link-local address conflicts. If both the automatic generation and manual assignment methods are used, the manual assignment takes precedence.

·     If you first use automatic generation and then manual assignment, the manually assigned link-local address overwrites the automatically generated one.

·     If you first use manual assignment and then automatic generation, both of the following occur:

¡     The link-local address is still the manually assigned one.

¡     The automatically generated link-local address does not take effect. If you delete the manually assigned address, the automatically generated link-local address takes effect.

Configuring automatic generation of an IPv6 link-local address for an interface

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Configure the interface to automatically generate an IPv6 link-local address.

ipv6 address auto link-local

By default, no link-local address is configured on an interface.

After an IPv6 global unicast address is configured on the interface, a link-local address is generated automatically.

Manually assigning an IPv6 link-local address to an interface

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Manually assign an IPv6 link-local address to the interface.

ipv6 address ipv6-address link-local

By default, no link-local address is configured on an interface.

Configuring an IPv6 anycast address

4.     Enter system view.

system-view

5.     Enter interface view.

interface interface-type interface-number

6.     Configure an IPv6 anycast address.

ipv6 address { ipv6-address prefix-length | ipv6-address/prefix-length } anycast

By default, no IPv6 anycast address is configured on an interface.

Configuring path MTU discovery

Setting the interface MTU

About this task

IPv6 routers do not support packet fragmentation. If a packet exceeds the MTU of the output interface, the router discards the packet and sends a packet too big message to the source host. This message contains the interface MTU. The source host fragments the packet according to the returned MTU. To avoid traffic overload due to packet dropping, set a proper interface MTU.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Set the interface MTU.

ipv6 mtu size

By default, no interface MTU is set.

Setting a static path MTU for an IPv6 address

About this task

You can set a static path MTU for an IPv6 address. Before sending a packet to the IPv6 address, the device compares the output interface MTU with the static path MTU. If the packet size exceeds the smaller one of the two values, the device fragments the packet according to the smaller value. After sending the fragmented packets, the device dynamically finds the path MTU to a destination host (see "IPv6 path MTU discovery").

Procedure

1.     Enter system view.

system-view

2.     Set a static path MTU for an IPv6 address.

ipv6 pathmtu ipv6-address value

By default, no path MTU is set for any IPv6 address.

Setting the aging time for dynamic path MTUs

About this task

After the device dynamically discovers the path MTU to a destination host (see "IPv6 path MTU discovery"), it performs the following operations:

·     Sends packets to the destination host based on this path MTU.

·     Starts the aging timer for this path MTU.

When the aging timer expires, the device removes the dynamic path MTU and discovers the path MTU again.

Restrictions and guidelines

The aging time is invalid for a static path MTU.

Procedure

1.     Enter system view.

system-view

2.     Set the aging time for dynamic path MTUs.

ipv6 pathmtu age age-time

The default setting is 10 minutes.

Controlling sending ICMPv6 messages

Configuring the rate limit for ICMPv6 error messages

About this task

To avoid sending excessive ICMPv6 error messages within a short period that might cause network congestion, you can limit the rate at which ICMPv6 error messages are sent. A token bucket algorithm is used with one token representing one ICMPv6 error message.

A token is placed in the bucket at intervals until the maximum number of tokens that the bucket can hold is reached.

A token is removed from the bucket when an ICMPv6 error message is sent. When the bucket is empty, ICMPv6 error messages are not sent until a new token is placed in the bucket.

Procedure

1.     Enter system view.

system-view

2.     Set the bucket size and the interval for tokens to arrive in the bucket for ICMPv6 error messages.

ipv6 icmpv6 error-interval interval [ bucketsize ]

By default, the bucket allows a maximum of 10 tokens. A token is placed in the bucket at an interval of 100 milliseconds.

To disable the ICMPv6 rate limit, set the interval to 0 milliseconds.

Enabling replying to multicast echo requests

1.     Enter system view.

system-view

2.     Enable replying to multicast echo requests.

ipv6 icmpv6 multicast-echo-reply enable

By default, this feature is disabled.

Enabling sending ICMPv6 destination unreachable messages

About this task

The device sends the source the following ICMPv6 destination unreachable messages:

·     ICMPv6 No Route to Destination message—A packet to be forwarded does not match any route.

·     ICMPv6 Communication with Destination Administratively Prohibited message—An administrative prohibition is preventing successful communication with the destination. This is typically caused by an ACL on the device.

·     ICMPv6 Beyond Scope of Source Address message—The destination is beyond the scope of the source IPv6 address. For example, a packet's source IPv6 address is a link-local address, and its destination IPv6 address is a global unicast address.

·     ICMPv6 Address Unreachable message—The device fails to resolve the link layer address for the destination IPv6 address of a packet.

·     ICMPv6 Port Unreachable message—No port process on the destination device exists for a received UDP packet.

Restrictions and guidelines

An ICMPv6 destination unreachable message indicates that the destination is not reachable from the source device. Attackers can launch malicious attacks to make the device generate incorrect ICMPv6 destination unreachable messages, which will affect the function of the network. To protect the network from malicious attacks and decrease unnecessary network traffic, you can disable the sending of ICMPv6 destination unreachable messages.

Procedure

1.     Enter system view.

system-view

2.     Enable sending ICMPv6 destination unreachable messages.

ipv6 unreachables enable

By default, this feature is disabled.

Enabling sending ICMPv6 time exceeded messages

About this task

The device sends the source ICMPv6 time exceeded messages as follows:

·     If a received packet is not destined for the device and its hop limit is 1, the device sends an ICMPv6 hop limit exceeded in transit message to the source.

·     Upon receiving the first fragment of an IPv6 datagram destined for the device, the device starts a timer. If the timer expires before all fragments arrive, the device sends an ICMPv6 fragment reassembly time exceeded message to the source.

Restrictions and guidelines

If the device receives large numbers of malicious packets, its performance degrades greatly because it must send back ICMP time exceeded messages. To prevent such attacks, disable sending ICMPv6 time exceeded messages.

Procedure

1.     Enter system view.

system-view

2.     Enable sending ICMPv6 time exceeded messages.

ipv6 hoplimit-expires enable

The default setting is disabled.

Enabling sending ICMPv6 redirect messages

About this task

Upon receiving a packet from a host, the device sends an ICMPv6 redirect message to inform the host of a better next hop when the following conditions are met:

·     The interface receiving the packet is the interface forwarding the packet.

·     The selected route is not created or modified by any ICMPv6 redirect messages.

·     The selected route is not a default route.

·     The forwarded packet does not contain the routing extension header.

The ICMPv6 redirect feature simplifies host management by enabling hosts that hold few routes to optimize their routing table gradually. However, to avoid adding too many routes on hosts, this feature is disabled by default.

Procedure

1.     Enter system view.

system-view

2.     Enable sending ICMPv6 redirect messages.

ipv6 redirects enable

By default, sending ICMPv6 redirect messages is disabled.

Specifying the source address for ICMPv6 packets

About this task

Perform this task to specify the source IPv6 address for outgoing ping echo requests and ICMPv6 error messages. It is a good practice to specify the IPv6 address of the loopback interface as the source IPv6 address. This feature helps users to easily locate the sending device.

Restrictions and guidelines

If you specify an IPv6 address in the ping command, ping echo requests use the specified address as the source IPv6 address. If you do not specify an IPv6 address in the ping command, ping echo requests use the IPv6 address specified by the ipv6 icmpv6 source command.

Procedure

1.     Enter system view.

system-view

2.     Specify an IPv6 address as the source address for outgoing ICMPv6 packets.

ipv6 icmpv6 source ipv6-address

By default, the device uses the IPv6 address of the sending interface as the source IPv6 address for outgoing ICMPv6 packets.

Enabling discarding IPv6 packets that contain extension headers

About this task

This feature enables a device to discard a received IPv6 packet in which the extension headers cannot be processed by the device.

Procedure

1.     Enter system view

system-view

2.     Enable the device to discard IPv6 packets that contain extension headers.

ipv6 extension-header drop enable

By default, the device does not discard IPv6 packets that contain extension headers.

Display and maintenance commands for IPv6 basics

Execute display commands in any view and reset commands in user view.

For information about the display tcp statistics, display udp statistics, reset tcp statistics, and reset udp statistics command, see the IP performance commands in Network Connectivity Command Reference.

 

Task

Command

Display IPv6 FIB entries.

display ipv6 fib  [ ipv6-address [ prefix-length ] ]

Display ICMPv6 traffic statistics.

display ipv6 icmp statistics

Display IPv6 information about the interface.

display ipv6 interface [ interface-type [ interface-number ] ] [ brief ]

Display IPv6 prefix information about the interface.

display ipv6 interface interface-type interface-number prefix

Display the IPv6 path MTU information.

display ipv6 pathmtu { ipv6-address | { all | dynamic | static } [ count ] }

Display the IPv6 prefix information.

display ipv6 prefix [ prefix-number ]

Display brief information about IPv6 RawIP connections.

display ipv6 rawip

Display detailed information about IPv6 RawIP connections.

display ipv6 rawip verbose [ pcb pcb-index ]

Display IPv6 and ICMPv6 packet statistics.

display ipv6 statistics

Display brief information about IPv6 TCP connections.

display ipv6 tcp

Display detailed information about IPv6 TCP connections.

display ipv6 tcp verbose [ pcb pcb-index ]

Display brief information about IPv6 UDP connections.

display ipv6 udp

Display detailed information about IPv6 UDP connections.

display ipv6 udp verbose [ pcb pcb-index ]

Display IPv6 TCP traffic statistics.

display tcp statistics

Display IPv6 UDP traffic statistics.

display udp statistics

Clear path MTUs.

reset ipv6 pathmtu { all | dynamic | static }

Clear IPv6 and ICMPv6 packet statistics.

reset ipv6 statistics

Clear IPv6 TCP traffic statistics.

reset tcp statistics

Clear IPv6 UDP traffic statistics.

reset udp statistics

Basic IPv6 settings configuration examples

Example: Configuring basic IPv6 settings

Network configuration

As shown in Figure 5, the host, the AP, and the switch are connected through Ethernet ports. Add Ethernet ports to VLANs. Configure IPv6 addresses for VLAN interfaces and verify that they are connected. The switch can reach the host.

Enable IPv6 on the host to automatically obtain an IPv6 address through IPv6 ND.

Figure 5 Network diagram

 

Procedure

In this example, VLAN-interface 2 has been created on the switch.

1.     Configure wireless services on the AP. For more information, see WLAN access configuration in WLAN Access Configuration Guide.

2.     Configure the AP:

# Specify a global unicast address for VLAN-interface 2.

<AP> system-view

[AP] interface vlan-interface 2

[AP-Vlan-interface2] ipv6 address 3001::1/64

[AP-Vlan-interface2] quit

# Specify a global unicast address for VLAN-interface 1, and allow it to advertise RA messages. (No interface advertises RA messages by default.)

[AP] interface vlan-interface 1

[AP-Vlan-interface1] ipv6 address 2001::1/64

[AP-Vlan-interface1] undo ipv6 nd ra halt

[AP-Vlan-interface1] quit

3.     Configure the switch:

# Configure a global unicast address for VLAN-interface 2.

<Switch> system-view

[Switch] interface vlan-interface 2

[Switch-Vlan-interface2] ipv6 address 3001::2/64

[Switch-Vlan-interface2] quit

# Configure an IPv6 static route with destination IPv6 address 2001::/64 and next hop address 3001::1.

[Switch] ipv6 route-static 2001:: 64 3001::1

4.     Enable IPv6 for the host to automatically obtain an IPv6 address through IPv6 ND.

Verifying the configuration

# Display the IPv6 interface settings on the AP. IPv6 global unicast addresses configured on the interfaces are displayed.

[AP] display ipv6 interface vlan-interface 2

Vlan-interface2 current state: UP

Line protocol current state: UP

IPv6 is enabled, link-local address is FE80::20F:E2FF:FE00:2

  Global unicast address(es):

    3001::1, subnet is 3001::/64

  Joined group address(es):

    FF02::1

    FF02::2

    FF02::1:FF00:1

    FF02::1:FF00:2

  MTU is 1500 bytes

  ND DAD is enabled, number of DAD attempts: 1

  ND reachable time is 30000 milliseconds

  ND retransmit interval is 1000 milliseconds

  Hosts use stateless autoconfig for addresses

IPv6 Packet statistics:

  InReceives:                    25829

  InTooShorts:                   0

  InTruncatedPkts:               0

  InHopLimitExceeds:             0

  InBadHeaders:                  0

  InBadOptions:                  0

  ReasmReqds:                    0

  ReasmOKs:                      0

  InFragDrops:                   0

  InFragTimeouts:                0

  OutFragFails:                  0

  InUnknownProtos:               0

  InDelivers:                    47

  OutRequests:                   89

  OutForwDatagrams:              48

  InNoRoutes:                    0

  InTooBigErrors:                0

  OutFragOKs:                    0

  OutFragCreates:                0

  InMcastPkts:                   6

  InMcastNotMembers:             25747

  OutMcastPkts:                  48

  InAddrErrors:                  0

  InDiscards:                    0

  OutDiscards:                   0

[AP] display ipv6 interface vlan-interface 1

Vlan-interface1 current state: UP

Line protocol current state: UP

IPv6 is enabled, link-local address is FE80::20F:E2FF:FE00:1C0

  Global unicast address(es):

    2001::1, subnet is 2001::/64

  Joined group address(es):

    FF02::1

    FF02::2

    FF02::1:FF00:1

    FF02::1:FF00:1C0

  MTU is 1500 bytes

  ND DAD is enabled, number of DAD attempts: 1

  ND reachable time is 30000 milliseconds

  ND retransmit interval is 1000 milliseconds

  ND advertised reachable time is 0 milliseconds

  ND advertised retransmit interval is 0 milliseconds

  ND router advertisements are sent every 600 seconds

  ND router advertisements live for 1800 seconds

  Hosts use stateless autoconfig for addresses

IPv6 Packet statistics:

  InReceives:                    272

  InTooShorts:                   0

  InTruncatedPkts:               0

  InHopLimitExceeds:             0

  InBadHeaders:                  0

  InBadOptions:                  0

  ReasmReqds:                    0

  ReasmOKs:                      0

  InFragDrops:                   0

  InFragTimeouts:                0

  OutFragFails:                  0

  InUnknownProtos:               0

  InDelivers:                    159

  OutRequests:                   1012

  OutForwDatagrams:              35

  InNoRoutes:                    0

  InTooBigErrors:                0

  OutFragOKs:                    0

  OutFragCreates:                0

  InMcastPkts:                   79

  InMcastNotMembers:             65

  OutMcastPkts:                  938

  InAddrErrors:                  0

  InDiscards:                    0

  OutDiscards:                   0

# Display the IPv6 interface settings on the switch. The IPv6 global unicast address configured on VLAN-interface 2 are displayed.

[Switch] display ipv6 interface vlan-interface 2

Vlan-interface2 current state :UP

Line protocol current state :UP

IPv6 is enabled, link-local address is FE80::20F:E2FF:FE00:1234

  Global unicast address(es):

    3001::2, subnet is 3001::/64

  Joined group address(es):

    FF02::1

    FF02::2

    FF02::1:FF00:2

    FF02::1:FF00:1234

  MTU is 1500 bytes

  ND DAD is enabled, number of DAD attempts: 1

  ND reachable time is 30000 milliseconds

  ND retransmit interval is 1000 milliseconds

  Hosts use stateless autoconfig for addresses

IPv6 Packet statistics:

  InReceives:                    117

  InTooShorts:                   0

  InTruncatedPkts:               0

  InHopLimitExceeds:             0

  InBadHeaders:                  0

  InBadOptions:                  0

  ReasmReqds:                    0

  ReasmOKs:                      0

  InFragDrops:                   0

  InFragTimeouts:                0

  OutFragFails:                  0

  InUnknownProtos:               0

  InDelivers:                    117

  OutRequests:                   83

  OutForwDatagrams:              0

  InNoRoutes:                    0

  InTooBigErrors:                0

  OutFragOKs:                    0

  OutFragCreates:                0

  InMcastPkts:                   28

  InMcastNotMembers:             0

  OutMcastPkts:                  7

  InAddrErrors:                  0

  InDiscards:                    0

  OutDiscards:                   0

# Ping the AP on the switch to verify the connectivity.

[Switch] ping ipv6 -c 1 3001::1

Ping6(56 data bytes) 3001::2 --> 3001::1, press CTRL_C to break

56 bytes from 3001::1, icmp_seq=0 hlim=64 time=4.404 ms

 

--- Ping6 statistics for 3001::1 ---

1 packet(s) transmitted, 1 packet(s) received, 0.0% packet loss

round-trip min/avg/max/std-dev = 4.404/4.404/4.404/0.000 ms

# Ping the host on the switch to verify the connectivity.

[Switch] ping ipv6 -c 1 2001::15B:E0EA:3524:E791

Ping6(56 data bytes) 3001::2 --> 2001::15B:E0EA:3524:E791, press CTRL_C to break

56 bytes from 2001::15B:E0EA:3524:E791, icmp_seq=0 hlim=64 time=5.404 ms

 

--- Ping6 statistics for 2001::15B:E0EA:3524:E791 ---

1 packet(s) transmitted, 1 packet(s) received, 0.0% packet loss

round-trip min/avg/max/std-dev = 5.404/5.404/5.404/0.000 ms

# Ping the switch and the AP on the host to verify the connectivity, (Details not shown.)


Configuring IPv6 neighbor discovery

About IPv6 neighbor discovery

ICMPv6 messages used by IPv6 neighbor discovery

The IPv6 neighbor discovery (ND) process uses ICMP messages for address resolution, neighbor reachability verification, and neighboring device tracking.

Table 3 describes the ICMPv6 messages used by the IPv6 ND protocol.

Table 3 ICMPv6 messages used by ND

ICMPv6 message

Type

Function

Neighbor Solicitation (NS)

135

Acquires the link-layer address of a neighbor on the local link.

Verifies the reachability of a neighbor.

Detects duplicate addresses.

Neighbor Advertisement (NA)

136

Responds to an NS message.

Notifies the neighboring nodes of link layer changes.

Router Solicitation (RS)

133

Requests an address prefix and other configuration information for autoconfiguration after startup.

Router Advertisement (RA)

134

Responds to an RS message.

Advertises information, such as the Prefix Information options and flag bits.

Redirect

137

Informs the source host of a better next hop on the path to a particular destination when certain conditions are met.

Address resolution

This function is similar to ARP in IPv4. An IPv6 node acquires the link-layer addresses of neighboring nodes on the same link through NS and NA messages.

Figure 6 shows how Host A acquires the link-layer address of Host B on the same link. The address resolution procedure is as follows:

1.     Host A multicasts an NS message. The source address of the NS message is the IPv6 address of the sending interface of Host A. The destination address is the solicited-node multicast address of Host B. The NS message body contains the link-layer address of Host A and the target IPv6 address.

2.     After receiving the NS message, Host B determines whether the target address of the packet is its IPv6 address. If it is, Host B learns the link-layer address of Host A, and then unicasts an NA message containing its link-layer address.

3.     Host A acquires the link-layer address of Host B from the NA message.

Figure 6 Address resolution

Neighbor reachability detection

After Host A acquires the link-layer address of its neighbor Host B, Host A can use NS and NA messages to test the reachability of Host B as follows:

1.     Host A sends an NS message whose destination address is the IPv6 address of Host B.

2.     If Host A receives an NA message from Host B, Host A decides that Host B is reachable. Otherwise, Host B is unreachable.

Duplicate address detection

After Host A acquires an IPv6 address, it performs Duplicate Address Detection (DAD) to check whether the address is being used by any other node. This is similar to gratuitous ARP in IPv4. DAD is accomplished through NS and NA messages.

The DAD procedure is as follows:

1.     Host A sends an NS message. The source address is the unspecified address and the destination address is the corresponding solicited-node multicast address of the IPv6 address to be detected. The NS message body contains the detected IPv6 address.

2.     If Host B uses this IPv6 address, Host B returns an NA message that contains its IPv6 address.

3.     Host A knows that the IPv6 address is being used by Host B after receiving the NA message from Host B. If receiving no NA message, Host A decides that the IPv6 address is not in use and uses this address.

Figure 7 Duplicate address detection

Router/prefix discovery and stateless address autoconfiguration

Router/prefix discovery allows an IPv6 node to find the neighboring routers and learn the prefix and network configuration parameters of the network from receiving RA messages.

Stateless address autoconfiguration allows an IPv6 node to automatically generate an IPv6 address based on the information learned through router/prefix discovery.

A node performs router/prefix discovery and stateless address autoconfiguration as follows:

1.     At startup, a node sends an RS message to request configuration information from a router.

2.     The router returns an RA message containing the Prefix Information option and other configuration information. (The router also periodically sends an RA message.)

3.     The node automatically generates an IPv6 address and other configuration parameters according to the configuration information in the RA message.

The Prefix Information option contains an address prefix and the preferred lifetime and valid lifetime of the address prefix. A node updates the preferred lifetime and valid lifetime upon receiving a periodic RA message.

The generated IPv6 address is valid within the valid lifetime and becomes invalid when the valid lifetime expires.

After the preferred lifetime expires, the node cannot use the generated IPv6 address to establish new connections, but can receive packets destined for the IPv6 address. The preferred lifetime cannot be greater than the valid lifetime.

Redirection

Upon receiving a packet from a host, the gateway sends an ICMPv6 redirect message to inform the host of a better next hop when the following conditions are met:

·     The interface receiving the packet is the same as the interface forwarding the packet.

·     The selected route is not created or modified by an ICMPv6 redirect message.

·     The selected route is not a default route on the device.

·     The forwarded IPv6 packet does not contain the routing extension header.

Protocols and standards

·     RFC 4861, Neighbor Discovery for IP Version 6 (IPv6)

IPv6 neighbor discovery tasks at a glance

All IPv6 neighbor discovery tasks are optional.

·     Configuring a static neighbor entry

·     Setting the dynamic neighbor learning limit on an interface

·     Setting the aging timer for ND entries in stale state

·     Minimizing link-local ND entries

·     Setting the hop limit

·     Configuring RA message sending and parameters

·     Enabling advertising invalid delegated prefixes

·     Setting the maximum number of attempts to send an NS message for DAD

·     Enabling ND proxy

Configuring a static neighbor entry

About this task

A neighbor entry stores information about a link-local node. The entry can be created dynamically through NS and NA messages, or configured statically.

The device uniquely identifies a static neighbor entry by using the neighbor's IPv6 address and the number of the Layer 3 interface that connects to the neighbor. You can configure a static neighbor entry by using one of the following methods:

·     Method 1—Associate a neighbor's IPv6 address and link-layer address with the local Layer 3 interface.

·     Method 2—Associate a neighbor's IPv6 address and link-layer address with a Layer 2 port in a VLAN.

Restrictions and guidelines

You can use either of the methods to configure a static neighbor entry for a VLAN interface.

·     If you use Method 1, the device is required to resolve the Layer 2 port in the related VLAN.

·     If you use Method 2, make sure the Layer 2 port belongs to the specified VLAN and the corresponding VLAN interface already exists. After the configuration, the device associates the VLAN interface with the neighbor IPv6 address to identify the static neighbor entry.

Procedure

1.     Enter system view.

system-view

2.     Configure a static neighbor entry.

ipv6 neighbor ipv6-address mac-address { vlan-id port-type port-number | interface interface-type interface-number }

By default, no static neighbor entries exist.

Setting the dynamic neighbor learning limit on an interface

About this task

The device can dynamically acquire the link-layer address of a neighboring node through NS and NA messages and add it into the neighbor table. When the number of dynamic neighbor entries reaches the limit, the interface stops learning neighbor information.

This feature limits the neighbor table size. A large neighbor table will degrade the forwarding performance.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Set the dynamic neighbor learning limit on the interface.

ipv6 neighbors max-learning-num max-number

By default, an interface can learn a maximum of 2048 dynamic neighbor entries.

Setting the aging timer for ND entries in stale state

About this task

ND entries in stale state have an aging timer. If an ND entry in stale state is not refreshed before the timer expires, the ND entry changes to the delay state. If it is still not refreshed in 5 seconds, the ND entry changes to the probe state, and the device sends an NS message three times. If no response is received, the device deletes the ND entry.

Procedure

1.     Enter system view.

system-view

2.     Set the aging timer for ND entries in stale state.

ipv6 neighbor stale-aging aging-time

The default setting is 240 minutes.

Minimizing link-local ND entries

About this task

Perform this task to minimize link-local ND entries assigned to the hardware. Link-local ND entries refer to ND entries that contain link-local addresses.

By default, the device assigns all ND entries to the hardware. With this feature enabled, the newly learned link-local ND entries are not assigned to the hardware if the link-local addresses of the entries are not the next hops of any routes. This feature saves hardware resources.

This feature takes effect only on newly learned link-local ND entries.

Procedure

1.     Enter system view.

system-view

2.     Minimize link-local ND entries.

ipv6 neighbor link-local minimize

By default, the device assigns all ND entries to the hardware.

Setting the hop limit

About this task

You can set the hop limit value to fill in the Hop Limit field for IPv6 packets to be sent.

Procedure

1.     Enter system view.

system-view

2.     Set the value for the Hop Limit field in the IP header.

ipv6 hop-limit value

The default setting is 64.

Configuring RA message sending and parameters

About RA message parameters

You can enable an interface to send RA messages, and configure the interval for sending RA messages and parameters in RA messages. After receiving an RA message, a host can use these parameters to perform corresponding operations. Table 4 describes the configurable parameters in an RA message.

Table 4 Parameters in an RA message and their descriptions

Parameter

Description

Hop Limit

Maximum number of hops in RA messages. A host receiving the RA message fills the value in the Hop Limit field of sent IPv6 packets.

Prefix information

After receiving the prefix information, the hosts on the same link can perform stateless autoconfiguration.

MTU

Guarantees that all nodes on the link use the same MTU.

M flag

Determines whether a host uses stateful autoconfiguration to obtain an IPv6 address.

If the M flag is set to 1, the host uses stateful autoconfiguration (for example, from a DHCPv6 server) to obtain an IPv6 address. Otherwise, the host uses stateless autoconfiguration to generate an IPv6 address according to its link-layer address and the prefix information in the RA message.

O flag

Determines whether a host uses stateful autoconfiguration to obtain configuration information other than the IPv6 address.

If the O flag is set to 1, the host uses stateful autoconfiguration (for example, from a DHCPv6 server) to obtain configuration information other than the IPv6 address. Otherwise, the host uses stateless autoconfiguration.

Router Lifetime

Tells the receiving hosts how long the advertising router can live. If the lifetime of a router is 0, the router cannot be used as the default gateway.

Retrans Timer

If the device does not receive a response message within the specified time after sending an NS message, it retransmits the NS message.

Reachable Time

If the neighbor reachability detection shows that a neighbor is reachable, the device considers the neighbor reachable within the specified reachable time. If the device needs to send a packet to the neighbor after the specified reachable time expires, the device reconfirms whether the neighbor is reachable.

Router Preference

Specifies the router preference in an RA message. A host selects a router as the default gateway according to the router preference. If router preferences are the same, the host selects the router from which the first RA message is received.

DNS server option

DNS server information for IPv6 hosts. Hosts can obtain DNS server information from received RA messages instead of using DHCPv6.

DNS suffix information in DNS Search List (DNSSL) option

DNS suffix information for IPv6 hosts. Hosts can obtain DNS suffix information from received RA messages instead of using DHCPv6.

Restrictions and guidelines

The maximum interval for sending RA messages should be less than (or equal to) the router lifetime in RA messages. In this way, the router can be updated by an RA message before expiration.

The values of the NS retransmission timer and the reachable time configured for an interface are sent in RA messages to hosts. This interface sends NS messages at the interval of the NS retransmission timer and considers a neighbor reachable within the reachable time.

Enabling the sending of RA messages

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable the sending of RA messages.

undo ipv6 nd ra halt

The default setting is disabled.

4.     Set the maximum and minimum intervals for sending RA messages.

ipv6 nd ra interval max-interval min-interval

By default, the maximum interval for sending RA messages is 600 seconds, and the minimum interval is 200 seconds.

The device sends RA messages at random intervals between the maximum interval and the minimum interval.

The minimum interval should be less than or equal to 0.75 times the maximum interval.

Configuring parameters for RA messages

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Configure the prefix information in RA messages.

ipv6 nd ra prefix { ipv6-prefix prefix-length | ipv6-prefix/prefix-length } [ valid-lifetime preferred-lifetime [ no-autoconfig | off-link ] * | no-advertise ]

By default, no prefix information is configured for RA messages, and the IPv6 address of the interface sending RA messages is used as the prefix information. If the IPv6 address is manually configured, the prefix uses a fixed valid lifetime of 2592000 seconds (30 days) and a preferred lifetime of 604800 seconds (7 days). If the IPv6 address is automatically obtained, the prefix uses the valid lifetime and preferred lifetime configured for the IPv6 address.

4.     Turn off the MTU option in RA messages.

ipv6 nd ra no-advlinkmtu

By default, RA messages contain the MTU option.

5.     Specify unlimited hops in RA messages.

ipv6 nd ra hop-limit unspecified

By default, the maximum number of hops in RA messages is 64.

6.     Set the M flag bit to 1.

ipv6 nd autoconfig managed-address-flag

By default, the M flag bit is set to 0 in RA advertisements. Hosts receiving the advertisements will obtain IPv6 addresses through stateless autoconfiguration.

7.     Set the O flag bit to 1.

ipv6 nd autoconfig other-flag

By default, the O flag bit is set to 0 in RA advertisements. Hosts receiving the advertisements will acquire other configuration information through stateless autoconfiguration.

8.     Set the router lifetime in RA messages.

ipv6 nd ra router-lifetime time

By default, the router lifetime is three times as long as the maximum interval for advertising RA messages.

9.     Set the NS retransmission timer.

ipv6 nd ns retrans-timer value

By default, an interface sends NS messages every 1000 milliseconds, and the value of the Retrans Timer field in RA messages is 0.

10.     Set the router preference in RA messages.

ipv6 nd router-preference { high | low | medium }

By default, the router preference is medium.

11.     Set the reachable time.

ipv6 nd nud reachable-time time

By default, the neighbor reachable time is 30000 milliseconds, and the value of the Reachable Time field in sent RA messages is 0.

Specifying DNS server information in RA messages

About this task

The DNS server options in RA messages provide DNS server information for IPv6 hosts. The RA messages allow hosts to obtain their IPv6 addresses and the DNS server through stateless autoconfiguration. This method is useful in a network where DHCPv6 infrastructure is not provided.

One DNS server option contains one DNS server. All DNS server options are sorted in ascending order of the DNS server sequence number.

After you execute the ipv6 nd ra dns server command, the device immediately sends an RA message with the existing and newly specified DNS server information.

After you execute the undo ipv6 nd ra dns server command, the device immediately sends two RA messages.

·     The first RA message contains information about all DNS servers, including the DNS servers specified in the undo command with their lifetime set to 0 seconds.

·     The second RA message contains information about remaining DNS servers.

Each time the device sends an RA message from an interface, it immediately refreshes the RA message advertisement interval for that interface.

Restrictions and guidelines

You can configure a maximum of eight DNS servers on an interface.

The default lifetime of a DNS server is three times the maximum interval for advertising RA messages. To set the maximum interval, use the ipv6 nd ra interval command.

In an IPv6 environment, PPP users can obtain the IPv6 DNS server address through AAA authorization. This AAA-authorized IPv6 DNS server address is also carried in RA messages. If an interface obtains the AAA-authorized and manually specified IPv6 DNS server addresses, the RA messages contain both, with the AAA-authorized address in the front. When the two addresses conflict, the AAA-authorized DNS-related attributes are used.

For more information about the PPP support for IPv6, see PPP configuration in Network Connectivity Configuration Guide.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Specify DNS server information to be advertised in RA messages.

ipv6 nd ra dns server ipv6-address [ seconds | infinite ] sequence seqno

By default, no DNS server information is specified and RA messages do not contain DNS server options.

Specifying DNS suffix information in RA messages

About this task

The DNSSL option in RA messages provides suffix information for IPv6 hosts. The RA messages allow hosts to obtain their IPv6 addresses and the DNS suffix through stateless autoconfiguration. This method is useful in a network where DHCPv6 infrastructure is not provided.

One DNSSL option contains one DNS suffix. All DNSSL options are sorted in ascending order of the sequence number of the DNS suffix.

After you execute the ipv6 nd ra dns search-list command, the device immediately sends an RA message with the existing and newly specified DNS suffix information.

After you execute the undo ipv6 nd ra dns search-list command, the device immediately sends two RA messages.

·     The first RA message contains information about all DNS suffixes, including DNS suffixes specified in the undo command with their lifetime set to 0 seconds.

·     The second RA message contains information about remaining DNS suffixes.

Each time the device sends an RA message from an interface, it immediately refreshes the RA message advertisement interval for that interface.

Restrictions and guidelines

You can configure a maximum of eight DNS suffixes on an interface.

The default lifetime of a DNS suffix is three times the maximum interval for advertising RA messages. To set the maximum interval, use the ipv6 nd ra interval command.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Specify DNS suffix information to be advertised in RA messages.

ipv6 nd ra dns search-list domain-name [ seconds | infinite ] sequence seqno

By default, no DNS suffix information is specified and RA messages do not contain DNS suffix options.

Suppressing advertising DNS information in RA messages

About this task

Perform this task to suppress the device from advertising information about DNS server addresses and DNS suffixes in RA messages.

Whether enabling this feature on an interface will trigger sending RA message immediately depends on the interface configuration:

·     If the interface has DNS server information configured or has obtained an AAA-authorized DNS server address, the device immediately sends two RA messages. In the first message, the lifetime for DNS server addresses is 0 seconds. The second RA message does not contain any DNS server options.

·     If the interface has no DNS server information specified or no AAA-authorized DNS server address assigned, no RA messages are triggered.

If you specify a new DNS server or remove a DNS server on the interface after enabling DNS server suppression, the device immediately sends an RA message without any DNS server options.

Whether disabling this feature on an interface will trigger sending RA message immediately depends on the interface configuration:

·     If the interface has DNS server information configured or has obtained an AAA-authorized DNS server address, the device immediately sends an RA message containing the DNS server information.

·     If the interface has no DNS server information specified or no AAA-authorized DNS server address assigned, no RA messages are triggered.

Each time the device sends an RA message from an interface, it immediately refreshes the RA message advertisement interval for that interface.

The same suppression mechanism applies when you enable or disable DNS suffix suppression in RA messages.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable DNS server suppression in RA messages.

ipv6 nd ra dns server suppress

By default, DNS server suppression in RA messages is disabled.

4.     Enable DNS suffix suppression in RA messages.

ipv6 nd ra dns search-list suppress

By default, DNS suffix suppression in RA messages is disabled.

Enabling advertising invalid delegated prefixes

About this task

An interface can generate an IPv6 address based on a prefix, which is assigned by the DHCPv6 server. When the assigned prefix goes invalid, the device does not advertise RA messages for the event by default. In this case, endpoints that use this prefix are not aware of the event, and continue using the IPv6 addresses generated based on the prefix, causing communication failures. To avoid this problem, you can use this feature. When a DHCPv6 server-assigned prefix goes invalid, the device sends out RA messages immediately. In the message, the preferred lifetime and valid lifetime are both set to 0, announcing that the prefix is invalid. Upon receiving the advertisement, endpoints will no longer use the IPv6 addresses generated based on the prefix. For more information about DHCPv6 server, see DHCPv6 server configuration in Network Connectivity Configuration Guide.

Restrictions and guidelines

RA messages are suppressed by default. To disable RA message suppression, use the undo ipv6 nd ra halt command.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable advertising invalid delegated prefixes.

ipv6 nd ra invalid-delegated-prefix advertise enable

By default, advertising invalid delegated prefixes is disabled.

Setting the maximum number of attempts to send an NS message for DAD

About this task

An interface sends an NS message for DAD for an obtained IPv6 address. The interface resends the NS message if it does not receive a response within the time specified by the ipv6 nd ns retrans-timer command. If the interface receives no response after making the maximum attempts specified by the ipv6 nd dad attempts command, the interface uses the IPv6 address.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Set the number of attempts to send an NS message for DAD.

ipv6 nd dad attempts interval

The default setting is 1. When the interval argument is set to 0, DAD is disabled.

Enabling ND proxy

About ND proxy

ND proxy enables a device to answer an NS message requesting the hardware address of a host on another network. With ND proxy, hosts in different broadcast domains can communicate with each other as they would on the same network.

ND proxy includes common ND proxy and local ND proxy.

Common ND proxy

As shown in Figure 8, Interface A with IPv6 address 4:1::99/64 and Interface B with IPv6 address 4:2::99/64 belong to different subnets. Host A and Host B reside on the same network but in different broadcast domains.

Figure 8 Application environment of ND proxy

Because Host A's IPv6 address is on the same subnet as Host B's, Host A directly sends an NS message to obtain Host B's MAC address. However, Host B cannot receive the NS message because they belong to different broadcast domains.

To solve this problem, enable common ND proxy on Interface A and Interface B of the device. The device replies to the NS message from Host A, and forwards packets from other hosts to Host B.

Local ND proxy

As shown in Figure 9, Host A belongs to VLAN 2 and Host B belongs to VLAN 3. Host A and Host B connect to Port B1 and Port B3, respectively.

Figure 9 Application environment of local ND proxy

Because Host A's IPv6 address is on the same subnet as Host B's, Host A directly sends an NS message to obtain Host B's MAC address. However, Host B cannot receive the NS message because they belong to different VLANs.

To solve this problem, enable local ND proxy on Interface A of Device A so that Device A can forward messages between Host A and Host B.

Local ND proxy implements Layer 3 communication for two hosts in the following cases:

·     The two hosts connect to ports of the same device and the ports must be in different VLANs.

·     The two hosts connect to isolated Layer 2 ports in the same isolation group of a VLAN.

Enabling common ND proxy

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable common ND proxy.

proxy-nd enable

By default, common ND proxy is disabled.

Enabling local ND proxy

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Enable local ND proxy.

local-proxy-nd enable

By default, local ND proxy is disabled.

Display and maintenance commands for IPv6 ND

Execute display commands in any view and reset commands in user view.

 

Task

Command

Display the total number of neighbor entries.

display ipv6 neighbors { { all | dynamic | static }| interface interface-type interface-number | vlan vlan-id } count

Display neighbor information.

display ipv6 neighbors { ipv6-address | all | dynamic | interface interface-type interface-number | static | vlan vlan-id } [ verbose ]

Clear IPv6 neighbor information.

reset ipv6 neighbors { all | dynamic | interface interface-type interface-number | static }