Table of Contents

Chapter 1 IP Addressing Configuration. 1-1

1.1 IP Addressing Overview. 1-1

1.1.1 IP Address Classes. 1-1

1.1.2 Special Case IP Addresses. 1-2

1.1.3 Subnetting and Masking. 1-2

1.2 Configuring IP Addresses. 1-3

1.3 Displaying IP Addressing Configuration. 1-4

1.4 IP Address Configuration Examples. 1-5

1.4.1 IP Address Configuration Example I 1-5

Chapter 2 IP Performance Configuration. 2-1

2.1 IP Performance Overview. 2-1

2.1.1 Introduction to IP Performance Configuration. 2-1

2.1.2 Introduction to FIB. 2-1

2.2 Configuring IP Performance. 2-1

2.2.1 Introduction to IP Performance Configuration Tasks. 2-1

2.2.2 Configuring TCP Attributes. 2-1

2.2.3 Disabling ICMP to Send Error Packets. 2-2

2.3 Displaying and Maintaining IP Performance Configuration. 2-3

 

Chapter 1  IP Addressing Configuration

1.1  IP Addressing Overview

1.1.1  IP Address Classes

IP addressing uses a 32-bit address to identify each host on a network. An example is 01010000100000001000000010000000 in binary. To make IP addresses in 32-bit form easier to read, they are written in dotted decimal notation, each being four octets in length, for example, 10.1.1.1 for the address just mentioned.

Each IP address breaks down into two parts:

l           Net ID: The first several bits of the IP address defining a network, also known as class bits.

l           Host ID: Identifies a host on a network.

For administration sake, IP addresses are divided into five classes, as shown in the following figure (in which the blue parts represent the address class).

Figure 1-1 IP address classes

Table 1-1 describes the address ranges of these five classes. Currently, the first three classes of IP addresses are used in quantity.

Table 1-1 IP address classes and ranges

Class	Address range	Description
A	0.0.0.0 to 127.255.255.255	Address 0.0.0.0 means this host no this network. This address is used by a host at bootstrap when it does not know its IP address. This address is never a valid destination address. Addresses starting with 127 are reserved for loopback test. Packets destined to these addresses are processed locally as input packets rather than sent to the link.
B	128.0.0.0 to 191.255.255.255	––
C	192.0.0.0 to 223.255.255.255	––
D	224.0.0.0 to 239.255.255.255	Multicast address.
E	240.0.0.0 to 255.255.255.255	Reserved for future use except for the broadcast address 255.255.255.255.

 

1.1.2  Special Case IP Addresses

The following IP addresses are for special use, and they cannot be used as host IP addresses:

l           IP address with an all-zeros net ID: Identifies a host on the local network. For example, IP address 0.0.0.16 indicates the host with a host ID of 16 on the local network.

l           IP address with an all-zeros host ID: Identifies a network.

l           IP address with an all-ones host ID: Identifies a directed broadcast address. For example, a packet with the destination address of 192.168.1.255 will be broadcasted to all the hosts on the network 192.168.1.0.

1.1.3  Subnetting and Masking

Subnetting was developed to address the risk of IP address exhaustion resulting from fast expansion of the Internet. The idea is to break a network down into smaller networks called subnets by using some bits of the host ID to create a subnet ID. To identify the boundary between the host ID and the combination of net ID and subnet ID, masking is used.

Each subnet mask comprises 32 bits related to the corresponding bits in an IP address. In a subnet mask, the part containing consecutive ones identifies the combination of net ID and subnet ID whereas the part containing consecutive zeros identifies the host ID.

Figure 1-2 shows how a Class B network is subnetted.

Figure 1-2 Subnet a Class B network

While allowing you to create multiple logical networks within a single Class A, B, or C network, subnetting is transparent to the rest of the Internet. All these networks still appear as one. As subnetting adds an additional level, subnet ID, to the two-level hierarchy with IP addressing, IP routing now involves three steps: delivery to the site, delivery to the subnet, and delivery to the host.

In the absence of subnetting, some special addresses such as the addresses with the net ID of all zeros and the addresses with the host ID of all ones, are not assignable to hosts. The same is true of subnetting. When designing your network, you should note that subnetting is somewhat a tradeoff between subnets and accommodated hosts. For example, a Class B network can accommodate 65,534 (2¹⁶ – 2. Of the two deducted Class B addresses, one with an all-ones host ID is the broadcast address and the other with an all-zeros host ID is the network address) hosts before being subnetted. After you break it down into 512 (2⁹) subnets by using the first 9 bits of the host ID for the subnet, you have only 7 bits for the host ID and thus have only 126 (2⁷ – 2) hosts in each subnet. The maximum number of hosts is thus 64,512 (512 × 126), 1022 less after the network is subnetted.

Class A, B, and C networks, before being subnetted, use these default masks (also called natural masks): 255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.

1.2  Configuring IP Addresses

S3100 Series Ethernet Switches support assigning IP addresses to VLAN interfaces and loopback interfaces. Besides directly assigning an IP address to a VLAN interface, you may configure a VLAN interface to obtain an IP address through BOOTP or DHCP as alternatives. If you change the way an interface obtains an IP address, from manual assignment to BOOTP for example, the IP address obtained from BOOTP will overwrite the old one manually assigned.

 

 

Table 1-2 Configure an IP address to an interface

Operation	Command	Remarks
Enter system view	system-view	––
Enter interface view	interface interface-type interface-number	––
Assign an IP address to the Interface	ip address ip-address { mask | mask-length }	Required No IP address is assigned by default.

 

 

1.3  Displaying IP Addressing Configuration

After the above configuration, you can execute the display command in any view to display the operating status and configuration on the interface to verify your configuration.

Table 1-3 Display IP addressing configuration

Operation	Command	Remarks
Display information about a specified or all Layer 3 interfaces	display ip interface [ interface-type interface-number ]	Available in any view
Display brief configuration information about a specified or all Layer 3 interfaces	display ip interface brief [ interface-type [ interface-number ] ]

 

1.4  IP Address Configuration Examples

1.4.1  IP Address Configuration Example I

I. Network requirement

Assign IP address 129.2.2.1 with mask 255.255.255.0 to VLAN interface 1 of the switch.

II. Network diagram

Figure 1-3 Network diagram for IP address configuration

III. Configuration procedure

# Configure an IP address for VLAN interface 1.

<Switch> system-view

[Switch] interface Vlan-interface 1

[Switch-Vlan-interface1] ip address 129.2.2.1 255.255.255.0

 

Chapter 2  IP Performance Configuration

2.1  IP Performance Overview

2.1.1  Introduction to IP Performance Configuration

In some network environments, you need to adjust the IP parameters to achieve best network performance. The IP performance configuration supported by S3100 Series Ethernet Switches includes:

l           Configuring TCP attributes

l           Disabling ICMP to send error packets

2.1.2  Introduction to FIB

Every switch stores a forwarding information base (FIB). FIB is used to store the forwarding information of the switch and guide Layer 3 packet forwarding.

You can know the forwarding information of the switch through the FIB table. Each FIB entry includes: destination address/mask length, next hop, current flag, timestamp, and outbound interface.

When the switch is running normally, the contents of the FIB and the routing table are the same.

2.2  Configuring IP Performance

2.2.1  Introduction to IP Performance Configuration Tasks

Table 2-1 Introduction to IP performance configuration tasks

Configuration task	Description	Related section
Configure TCP attributes	Optional	2.2.2
Disable ICMP to send error packets	Optional	2.2.3

 

2.2.2  Configuring TCP Attributes

TCP optional parameters that can be configured include:

l           synwait timer: When sending a SYN packet, TCP starts the synwait timer. If no response packets are received before the synwait timer times out, the TCP connection is not successfully created.

l           finwait timer: When the TCP connection is changed into FIN_WAIT_2 state, finwait timer will be started. If no FIN packets are received within the timer timeout, the TCP connection will be terminated. If FIN packets are received, the TCP connection state changes to TIME_WAIT. If non-FIN packets are received, the system restarts the timer from receiving the last non-FIN packet. The connection is broken after the timer expires.

l           Size of TCP receive/send buffer

Table 2-2 Configure TCP attributes

Operation	Command	Remarks
Enter system view	system-view	—
Configure TCP synwait timer’s timeout value	tcp timer syn-timeout time-value	Optional By default, the timeout value is 75 seconds.
Configure TCP finwait timer’s timeout value	tcp timer fin-timeout time-value	Optional By default, the timeout value is 675 seconds.
Configure the size of TCP receive/send buffer	tcp window window-size	Optional By default, the buffer is 8 kilobytes.

 

2.2.3  Disabling ICMP to Send Error Packets

Sending error packets is a major function of ICMP protocol. In case of network abnormalities, ICMP packets are usually sent by the network or transport layer protocols to notify corresponding devices so as to facilitate control and management.

By default, S3100 Series Ethernet Switches support sending ICMP redirect and destination unreachable packets.

Although sending ICMP error packets facilitate control and management, it still has the following disadvantages:

l           Sending a lot of ICMP packets will increase network traffic.

l           If receiving a lot of malicious packets that cause it to send ICMP error packets, the device’s performance will be reduced.

l           As the ICMP redirection function increases the routing table size of a host, the host’s performance will be reduced if its routing table becomes very large.

l           If a host sends malicious ICMP destination unreachable packets, end users may be affected.

You can disable the device from sending such ICMP error packets for reducing network traffic and preventing malicious attacks.

Table 2-3 Disable sending ICMP error packets

Operation	Command	Remarks
Enter system view	system-view	—
Disable sending ICMP redirects	undo icmp redirect send	Required Enabled by default
Disable sending ICMP destination unreachable packets	undo icmp unreach send	Required Enabled by default

 

2.3  Displaying and Maintaining IP Performance Configuration

After the above configurations, you can execute the display command in any view to display the running status to verify your IP performance configuration.

Use the reset command in user view to clear the IP, TCP, and UDP traffic statistics.

Table 2-4 Display and maintain IP performance

Operation	Command	Remarks
Display TCP connection status	display tcp status	You can execute the display command in any view.
Display TCP connection statistics	display tcp statistics
Display UDP traffic statistics	display udp statistics
Display IP traffic statistics	display ip statistics
Display ICMP traffic statistics	display icmp statistics
Display the current socket information of the system	display ip socket [ socktype sock-type ] [ task-id socket-id ]
Display the forwarding information base (FIB) entries	display fib
Display the FIB entries matching the destination IP address	display fib ip-address1 [ { mask1 | mask-length1 } [ ip-address2 { mask2 | mask-length2 } | longer ] | longer ]
Display the FIB entries filtering through a specific ACL	display fib acl number
Display the FIB entries in the buffer which begin with, include or exclude the specified character string.	display fib | { begin | include | exclude } regular-expression
Display the total number of the FIB entries	display fib statistics
Clear IP traffic statistics	reset ip statistics	You can execute the reset command in user view.
Clear TCP traffic statistics	reset tcp statistics
Clear UDP traffic statistics	reset udp statistics