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.

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

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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:

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.

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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.

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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.

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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

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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, 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

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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 for IPv6 packets

¡ Setting the aging time for dynamic path MTUs

¡ Setting a static path MTU for an IPv6 address

3. (Optional.) Controlling sending and receiving ICMPv6 messages

¡ Disabling receiving a specific type of ICMPv6 messages

¡ Disabling sending a specific type of 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 router renumbering

5. (Optional.) Enabling IPv6 virtual fragment reassembly

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

7. (Optional.) Configuring TCP congestion control algorithm for IPv6 TCP proxy

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 about advertising invalid delegated prefixes, see IPv6 neighbor discovery configuration in Network Connectivity Configuration Guide.

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

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. 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 for IPv6 packets

About this task

If a packet exceeds the MTU of the forwarding interface, the intermediate device discards the packet and sends a packet too big message to the source device.

Restrictions and guidelines

To avoid extra traffic overhead 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 for IPv6 packets.

ipv6 mtu size

By default, no interface MTU is 1280 bytes.

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.

Setting a static path MTU for an IPv6 address

About this task

In an IPv6 network, the intermediate devices do not fragment packets. packet fragmentation is performed by the source device, eliminating working load on intermediate devices.

Typically, the source device determines the dynamic Path MTU as described in "IPv6 path MTU discovery" and uses this Path MTU to fragment packets before sending. In some scenarios, to protect the network against large packet attack, you need to execute the ipv6 pathmtu command to set a static Path MTU for an IPv6 address, controlling the packet size from the source to the destination.

When a source device sends a packet to the destination, it does not use the interface MTU setting of the sending interface if it identities that the destination IPv6 address has a static path MTU configured. Instead, it compares the interface MTU and the static Path MTU of the destination IPv6 address with the packet size.

· If the packet size is smaller than or equal to the smaller one of the two MTU values, the device sends the packet directly.

· If the packet size is larger than the smaller one of the two values, the device fragments the packet according to the smaller value.

During the sending process, if the source device receives a Packet Too Big message from an intermediate device, the packet sending fails.

Restrictions and guidelines

The priority of the static Path MTU is higher than the dynamic Path MTU, and the static Path MTU never ages out.

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 static Path MTU is specified.

Controlling sending and receiving ICMPv6 messages

Disabling receiving a specific type of ICMPv6 messages

About this task

By default, the device receives all types of ICMPv6 messages. Such a setting might affect device performance if a large number of ICMPv6 responses are received within a short time. To solve this issue, you can perform this task to disable the device from receiving a specific type of ICMPv6 messages.

Restrictions and guidelines

Disabling receiving ICMPv6 messages of a specific type might affect network operation. Please use this feature with caution.

Procedure

1. Enter system view.

system-view

2. Disable the device from receiving a specific type of ICMPv6 messages.

undo ipv6 icmpv6 { name name | type type code code } receive enable

By default, the device can receive ICMPv6 messages of all types.

Disabling sending a specific type of ICMPv6 messages

About this task

By default, the device sends all types of ICMPv6 messages except Destination Unreachable and Redirect messages (packet type field set to 1 and 137, respectively). Attackers might obtain device information from specific types of ICMPv6 messages, causing security issues. For information about the packet type field, see RFC4443.

For security purposes, you can perform this task to disable the device from sending specific types of ICMPv6 messages.

Restrictions and guidelines

Disabling sending ICMPv6 messages of a specific type might affect network operation. Please use this feature with caution.

To enable sending Destination Unreachable, Time Exceeded, or Redirect messages, you can perform one of the following tasks:

· Execute the ipv6 icmpv6 send enable command.

· Execute one of the following commands as needed:

¡ ipv6 unreachables enable

¡ ipv6 hoplimit-expires enable

¡ ipv6 redirects enable

Procedure

1. Enter system view.

system-view

2. Disable the device from sending a specific type of ICMPv6 messages.

undo ipv6 icmpv6 { name name | type type code code } send enable

By default, the device sends all types of ICMPv6 messages except Destination Unreachable and Redirect 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 (packet type field set to 1):

· 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 a firewall or 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.

For information about the packet type field, see RFC4443.

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, the device does not send ICMPv6 destination unreachable messages.

Enabling sending ICMPv6 time exceeded messages

About this task

The device sends the source ICMPv6 time exceeded messages (packet type field set to 3) 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.

For information about the packet type field, see RFC4443.

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

By default, the device sends ICMPv6 time exceeded messages.

Enabling sending ICMPv6 redirect messages

About this task

Upon receiving a packet from a host, the device sends an ICMPv6 redirect message (packet type field set to 137) 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 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.

For information about the packet type field, see RFC4443.

Procedure

1. Enter system view.

system-view

2. Enable sending ICMPv6 redirect messages.

ipv6 redirects enable

By default, the device does not send ICMPv6 redirect messages.

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 router renumbering

About this task

Router renumbering allows reconfiguration of address prefixes on IPv6 routers.

As shown in Figure 4, Router A sends RR messages to the downstream devices (Router B, Router C, and Router D) to change their prefix to be advertised in RAs.

Figure 4 Network diagram

Restrictions and guidelines

You must enable router renumbering on the downstream router interfaces before they receive and process RR packets.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable router renumbering.

ipv6 router-renumber enable

By default, router renumbering is disabled.

Enabling IPv6 virtual fragment reassembly

About this task

To prevent each service module from processing packet fragments that do not arrive in order, you can enable the IPv6 VFR feature. This feature virtually reassembles the fragments of an IPv6 datagram through caching, sequencing, and fragment check, ensuring fragments arrive at each service module in order.

IPv6 VFR drops fragments in the following conditions:

· If two consecutive incoming fragments are identical or overlap with each other, VFR discards all fragments within a fragment chain.

· If the fragments of a datagram (in a reassembly) are not reassembled within the timeout interval, VFR discards all the fragments of the reassembly.

The enabling status of IPv6 VFR can be managed at CLI or the enabling status of a service module that can call VFR. IPv6 VRF is enabled in either of the following conditions:

· A service module that can call it is enabled.

· The ipv6 virtual-reassembly enable command is executed. If fragment reassembly is required, but a service module cannot call it, execute this command at CLI.

The command enables the LPU to reassemble the IPv6 fragments of a packet if all the fragments arrive at it.

IPv6 VFR and the services that can call it require that all IPv6 fragments of an IPv6 packet must be received by the same device. If not, fragments are cached by different devices and will be discarded due to timeout.

Procedure

1. Enter system view.

system-view

2. Enable IPv6 virtual fragment reassembly.

ipv6 virtual-reassembly enable

By default, IPv6 virtual fragment reassembly is disabled.

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.

Configuring TCP congestion control algorithm for IPv6 TCP proxy

About this task

When you perform this task, you can configure one of the following TCP congestion control algorithms:

· Reno—Use this algorithm in scenarios with low latency and low bandwidth. In scenarios with high latency and high bandwidth, the speed of data transmission takes a long time to reach the maximum and thus the bandwidth utilization rate is low.

Reno is an early TCP congestion control algorithm that increases the number of congestion windows on receipt of ACK messages.

· BIC—Use this algorithm in scenarios with high bandwidth and low packet loss ratio.

BIC can make good use of remaining bandwidth resources and improve throughput, because this algorithm does not slow down packet sending as long as no packet loss occurs. However, the transmission latency of this algorithm is high. This algorithm will reduce the number of congestion windows when transmission errors cause packet loss.

· BBR—Use this algorithm in scenarios with high bandwidth, high latency, and packet loss.

BBR does not use packet loss as a congestion signal. In a scenario with high packet loss ratio, this algorithm can ensure high throughput and reduce transmission latency effectively. BBRv2 improves intra-protocol fairness by balancing aggressiveness.

Restrictions and guidelines

This task does not take effect on the modules that support TCP congestion control algorithm configuration. The TCP congestion control algorithm used by such a module depends on its configuration.

The modules that do not support TCP congestion control algorithm configuration use the same algorithm as the TCP proxy module.

Procedure

1. Enter system view.

system-view

2. Specify a TCP congestion control algorithm for IPv6 TCP proxy.

ipv6 tcp-proxy congestion-method { bbrv1 | bbrv2 | bic | reno }

By default, the TCP congestion control algorithm is Reno for IPv6 TCP proxy.

Verifying and maintaining basic IPv6 settings

Verifying basic IPv6 configuration

Perform display tasks in any view.

· 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 prefix information.

display ipv6 prefix [ prefix-number ]

Displaying information about IPv6 protocol connections

Displaying information about IPv6 RawIP connections

Perform display tasks in any view.

· Display brief information about IPv6 RawIP connections.

display ipv6 rawip [ slot slot-number ]

· Display detailed information about IPv6 RawIP connections.

display ipv6 rawip verbose [ slot slot-number [ pcb pcb-index ] ]

Displaying information about IPv6 TCP connections

Perform display tasks in any view.

· Display brief information about IPv6 TCP connections.

display ipv6 tcp [ slot slot-number ]

· Display detailed information about IPv6 TCP connections.

display ipv6 tcp verbose [ slot slot-number [ pcb pcb-index ] ]

Displaying information about IPv6 UDP connections

Perform display tasks in any view.

· Display brief information about IPv6 UDP connections.

display ipv6 udp [ slot slot-number ]

· Display detailed information about IPv6 UDP connections.

display ipv6 udp verbose [ slot slot-number [ pcb pcb-index ] ]

Displaying and clearing IPv6 protocol packet statistics

Displaying IPv6 protocol packet statistics

Perform display tasks in any view.

· Display IPv6 and ICMPv6 packet statistics.

display ipv6 statistics [ slot slot-number ]

· Display ICMPv6 traffic statistics.

display ipv6 icmp statistics [ slot slot-number ]

· Display IPv6 UDP traffic statistics.

display udp statistics [ slot slot-number ]

For information about this command, see the IP performance optimization commands in Network Connectivity Command Reference.

Clearing IPv6 protocol packet statistics

Perform clear tasks in user view.

· Clear IPv6 and ICMPv6 packet statistics.

reset ipv6 statistics [ slot slot-number ]

· Clear IPv6 UDP traffic statistics.

reset udp statistics

For information about this command, see the IP performance optimization commands in Network Connectivity Command Reference.

Displaying and clearing IPv6 Path MTU information

Displaying IPv6 Path MTU information

To display IPv6 Path MTU information, execute the following command in any view:

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

Clearing IPv6 Path MTU information

To clear IPv6 Path MTU information, execute the following command in user view:

reset ipv6 pathmtu { all | dynamic | static }

Displaying and clearing routing renumbering statistics

Displaying routing renumbering statistics

To display routing renumbering statistics, execute the following command in any view:

display ipv6 router-renumber statistics

Clearing routing renumbering statistics

To clear routing renumbering statistics, execute the following command in user view:

reset ipv6 router-renumber statistics

Displaying IPv6 FIB entries

To display IPv6 FIB entries, execute the following command in any view:

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

Displaying the differences in IPv6 FIB entries between the specified slots

To display the differences in IPv6 FIB entries between the specified slots, execute the following command in any view:

display ipv6 fib prefix diff [ all | [ ipv6-address [ prefix-length ] ] ] slot slot-number1 slot slot-number2

Basic IPv6 settings configuration examples

Example: Configuring basic IPv6 settings

Network configuration

As shown in Figure 5, an AC and an AP are connected through a switch. Add the Ethernet ports of the AC and AP to corresponding VLANs. Configure the IPv6 address of the AC on VLAN-interface 1. The AP obtains an IP address and the IP address of AC through DHCP. The AP establishes a CAPWAP tunnel with the AC.

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

Figure 5 Network diagram

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Procedure

1. Configure the AC:

# Configure the basic functions of the AC. For more information, see WLAN access configuration in WLAN Access Configuration Guide. (Details not shown.)

# Specify a global unicast address for VLAN-interface 1, and enable it to advertise RA messages. (An interface does not advertise RA messages by default.)

<AC> system-view

[AC] interface vlan-interface 1

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

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

2. Enable IPv6 for the client to automatically obtain an IPv6 address through IPv6 ND. (Details not shown.)

Verifying the configuration

# Display neighbor information for GigabitEthernet 1/0/2 on the AC.

[AC-Vlan-interface1] display ipv6 neighbors interface gigabitethernet 1/0/2

Type: S-Static D-Dynamic O-Openflow R-Rule IS-Invalid static

IPv6 address MAC address VID Interface State T Age

FE80::215:E9FF:FEA6:7D14 0015-e9a6-7d14 1 WLAN-BSS1/0/1 STALE D 1238

2001::15B:E0EA:3524:E791 0015-e9a6-7d14 1 WLAN-BSS1/0/1 STALE D 1248

The output shows that the IPv6 global unicast address that the client obtained is 2001::15B:E0EA:3524:E791.

# Display the IPv6 interface settings on the AC.

[AC-Vlan-interface1] 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::18C

FF02::1:FF00:1

FF02::1:FFB5:ED00

FF0E::18C

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

# Ping the AC from the client, and ping the client from the AC to verify that they are connected.

NOTE:

When you ping a link-local address, use the -i parameter to specify an interface for the link-local address.

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[AC-Vlan-interface1] ping ipv6 -c 1 2001::15B:E0EA:3524:E791

PING 2001::15B:E0EA:3524:E791 : 56 data bytes, press CTRL+C to break

Reply from 2001::15B:E0EA:3524:E791

bytes=56 Sequence=1 hop limit=63 time = 3 ms

--- 2001::15B:E0EA:3524:E791 ping statistics ---

1 packet(s) transmitted

1 packet(s) received

0.00% packet loss

round-trip min/avg/max = 3/3/3 ms

The output shows that the AC can ping the client. The client can also ping the AC.

05-Network Connectivity Configuration Guide

Simplified header format

Larger address space

Hierarchical address structure

Address autoconfiguration

Built-in security

QoS support

Enhanced neighbor discovery mechanism

Flexible extension headers

IPv6 address format

IPv6 address types

Unicast addresses

Multicast addresses

EUI-64 address-based interface identifiers

About this task

Restrictions and guidelines

Enabling stateless address autoconfiguration

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

Setting the interface MTU for IPv6 packets

About this task

Restrictions and guidelines

Procedure

Setting the aging time for dynamic path MTUs

About this task

Restrictions and guidelines

Procedure

Setting a static path MTU for an IPv6 address

About this task

Restrictions and guidelines

Procedure

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Restrictions and guidelines

Procedure

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Restrictions and guidelines

Procedure

About this task

Procedure

About this task

Restrictions and guidelines

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About this task

Restrictions and guidelines

Procedure

About this task

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

About this task

Procedure

Configuring TCP congestion control algorithm for IPv6 TCP proxy

About this task

Restrictions and guidelines

Procedure

Displaying information about IPv6 RawIP connections

Displaying information about IPv6 TCP connections

Displaying information about IPv6 UDP connections

Displaying IPv6 protocol packet statistics

Clearing IPv6 protocol packet statistics

Displaying IPv6 Path MTU information

Clearing IPv6 Path MTU information

Displaying routing renumbering statistics

Clearing routing renumbering statistics

Displaying the differences in IPv6 FIB entries between the specified slots

Network configuration

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