Configuring IP addressing· 1

IP addressing overview·· 1

IP address classes 1

Special IP addresses 2

Subnetting and masking· 2

Configuring IP addresses 2

Assigning an IP address to an interface· 3

Displaying and maintaining IP addressing· 3

IP addressing configuration example· 3

 

IP addressing overview

IP address classes

IP addressing uses a 32-bit address to identify each host on a network. To make addresses easier to read, they are written in dotted decimal notation, each address being four octets in length. For example, address 00001000000000010000000100000001 in binary is written as 10.1.1.1.

Each IP address breaks down into two parts:

·           Net ID—Identifies a network. The first several bits of a net ID, known as the class field or class bits, identify the class of the IP address.

·           Host ID—Identifies a host on a network.

IP addresses are divided into five classes, shown in Figure 1. The shaded areas represent the address class. The first three classes are widely used.

Figure 1 IP address classes

 

Table 1 IP address classes and ranges

Class	Address range	Description
A	0.0.0.0 to 127.255.255.255	The IP address 0.0.0.0 is used by a host at startup for temporary communication. 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	N/A
C	192.0.0.0 to 223.255.255.255	N/A
D	224.0.0.0 to 239.255.255.255	Multicast addresses.
E	240.0.0.0 to 255.255.255.255	Reserved for future use except for the broadcast address 255.255.255.255.

 

Special IP addresses

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

·           IP address with an all-zero 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.

·           IP address with an all-zero host ID—Identifies a network.

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

Subnetting and masking

Subnetting divides a network down into smaller networks called subnets by using some bits of the host ID to create a subnet ID.

Masking identifies the boundary between the host ID and the combination of net ID and subnet ID.

Each subnet mask comprises 32 bits that correspond to the bits in an IP address. In a subnet mask, consecutive ones represent the net ID and subnet ID, and consecutive zeros represent the host ID.

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

Figure 2 Subnet a Class B network

 

Subnetting increases the number of addresses that cannot be assigned to hosts. Therefore, using subnets means accommodating somewhat fewer hosts

For example, a Class B network without subnetting can accommodate 1022 more hosts than the same network subnetted into 512 subnets.

·           Without subnetting, 65,534 hosts (2¹⁶ – 2). (The two deducted addresses are the broadcast address, which has an all-one host ID, and the network address, which has an all-zero host ID.)

·           With subnetting, use the first 9 bits of the host-id for subnetting provides 512 (2⁹) subnets. However, only 7 bits remain available for the host ID. This allows 126 (2⁷ – 2) hosts in each subnet, a total of 64,512 hosts (512 × 126). 

Configuring IP addresses

An interface must have an IP address to communicate with other hosts. You can either manually assign an IP address for an interface, or configure the interface to obtain an IP address through PPP negotiation. If you change the way an interface obtains an IP address, the new IP address will overwrite the previous one.

 

NOTE: ·       This chapter only covers how to assign an IP address manually. ·       For how to obtain an IP address through PPP address negotiation, see Layer 2—WAN Configuration Guide.

 

Assigning an IP address to an interface

You may assign an interface one primary and multiple secondary IP addresses.

Generally, you only need to assign the primary address to an interface. In some cases, you need to assign secondary IP addresses to the interface. For example, if the interface connects to two subnets, you need to assign a primary IP address and a secondary IP address to the interface to enable the switch to communicate with all hosts on the LAN.

To assign an IP address to an interface:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter interface view.	interface interface-type interface-number	N/A
3.     Assign an IP address to the interface.	ip address ip-address { mask-length | mask } [ sub ]	No IP address is assigned by default

 

CAUTION: ·       An interface can have only one primary IP address. A newly configured primary IP address overwrites the previous one. ·       Do not assign an IP address to an interface that is configured to obtain an IP address through PPP negotiation. ·       The primary and secondary IP addresses of an interface can be located on the same network, but the IP addresses of different interfaces, the IP address of an interface and the IP address of any of its subinterface, but different interfaces on your device must reside on different network segments.

 

Displaying and maintaining IP addressing

 

Task	Command	Remarks
Display IP configuration information for a specified Layer 3 interface or all Layer 3 interfaces.	display ip interface [ interface-type interface-number ] [ | { begin | exclude | include } regular-expression ]	Available in any view
Display brief IP configuration information for a specified Layer 3 interface or all Layer 3 interfaces.	display ip interface [ interface-type [ interface-number ] ] brief [ | { begin | exclude | include } regular-expression ]	Available in any view

 

IP addressing configuration example

 

NOTE: By default, the Ethernet interface, VLAN interfaces, and aggregate interfaces are down. Before configuring them, bring them up with the undo shutdown command.

 

Network requirements

As shown in Figure 3, the VLAN-interface 1 on a switch is connected to a LAN comprising two segments: 172.16.1.0/24 and 172.16.2.0/24.

To enable the hosts on the two network segments to access the external network through the switch, and to enable the hosts on the two network segments to communicate with each other:

·           Assign a primary IP address and a secondary IP address to VLAN-interface 1 on the switch.

·           Set the primary IP address of the switch as the gateway of one host and the secondary IP address as the gateway of the other host.

Figure 3 Network diagram

 

Configuration procedure

# Assign a primary IP address and a secondary IP address to VLAN-interface 1.

<Switch> system-view

[Switch] interface vlan-interface 1

[Switch-Vlan-interface1] ip address 172.16.1.1 255.255.255.0

[Switch-Vlan-interface1] ip address 172.16.2.1 255.255.255.0 sub

# Set the gateway address to 172.16.1.1 on the PCs attached to the subnet 172.16.1.0/24, and to 172.16.2.1 on the PCs attached to the subnet 172.16.2.0/24.

# Ping a host on subnet 172.16.1.0/24 from the switch to check the connectivity.

<Switch> ping 172.16.1.2

  PING 172.16.1.2: 56  data bytes, press CTRL_C to break

    Reply from 172.16.1.2: bytes=56 Sequence=1 ttl=255 time=25 ms

    Reply from 172.16.1.2: bytes=56 Sequence=2 ttl=255 time=27 ms

    Reply from 172.16.1.2: bytes=56 Sequence=3 ttl=255 time=26 ms

    Reply from 172.16.1.2: bytes=56 Sequence=4 ttl=255 time=26 ms

    Reply from 172.16.1.2: bytes=56 Sequence=5 ttl=255 time=26 ms

 

  --- 172.16.1.2 ping statistics ---

    5 packet(s) transmitted

    5 packet(s) received

    0.00% packet loss

    round-trip min/avg/max = 25/26/27 ms

The output shows that the switch can communicate with the hosts on subnet 172.16.1.0/24.

# Ping a host on subnet 172.16.2.0/24 from the switch to check the connectivity.

<Switch> ping 172.16.2.2

  PING 172.16.2.2: 56  data bytes, press CTRL_C to break

    Reply from 172.16.2.2: bytes=56 Sequence=1 ttl=255 time=25 ms

    Reply from 172.16.2.2: bytes=56 Sequence=2 ttl=255 time=26 ms

    Reply from 172.16.2.2: bytes=56 Sequence=3 ttl=255 time=26 ms

    Reply from 172.16.2.2: bytes=56 Sequence=4 ttl=255 time=26 ms

    Reply from 172.16.2.2: bytes=56 Sequence=5 ttl=255 time=26 ms

 

  --- 172.16.2.2 ping statistics ---

    5 packet(s) transmitted

    5 packet(s) received

    0.00% packet loss

    round-trip min/avg/max = 25/25/26 ms

The output shows that the switch can communicate with the hosts on subnet 172.16.2.0/24.

# Ping a host on subnet 172.16.1.0/24 from a host on subnet 172.16.2.0/24 to check the connectivity. Host B can be successfully pinged from Host A.