This section describes how to configure and use user-defined loopback interfaces on the switch.
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NOTE: The |
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By default, each switch has an internal loopback interface (lo0
) with the IP address 127.0.0.1. This IP address is used only for internal traffic transmitted within the switch and is not used in packet headers in egress traffic sent to network devices.
You can configure up to seven other loopback interfaces (lo1
, lo2
, lo3
, and so on) on the switch to use to transmit network across the network. Each loopback interface can have multiple IP addresses. Routing protocols, such as RIP and OSPF, advertise the configured loopback addresses throughout a network or autonomous system.
User-defined loopback addresses provide the following benefits:
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A loopback interface is a virtual interface that is always up and reachable as long as at least one of the IP interfaces on the switch is operational. As a result, a loopback interface is useful for debugging tasks since its IP address can always be pinged if any other switch interface is up.
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You can use a loopback interface to establish a Telnet session, ping the switch, and access the switch through SNMP, SSH, and HTTP (WebAgent).
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A loopback IP address can be used by routing protocols. For example, you can configure the loopback IP address as the router ID used to identify the switch in an OSPF area. Because the loopback interface is always up, you ensure that the switch's router ID remains constant and that the OSPF network is protected from changes caused by downed interfaces.
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To configure a loopback interface, enter the interface loopback command at the global configuration level of the CLI:
Syntax
Creates a loopback interface, where <number> is a value from 1 to 7. Use the no form of the command to remove the loopback interface.
Note: You cannot remove the default loopback interface (number 0) with IP address 127.0.0.1.
You can configure up to thirty-two IP addresses on a loopback interface. To configure an IP address for the loopback interface, enter the ip address <ip address> command at the loopback interface configuration level as shown in the following example.
Note that when you configure an IP address for a loopback interface, you do not specify a network mask. The default subnet mask 255.255.255.255 is used.
A loopback interface configuration
HP Switch(config)# interface loopback 1 HP Switch(config)# ip address 10.1.1.1
To display the list of loopback interfaces which have been assigned IP addresses, enter the show ip command.
In the show ip command output, information about configured loopback interfaces is displayed below other IP configuration parameters, such as packet TTL and ARP age-out values, and VLAN IP configurations. The following example displays the IP addresses configured for two user-defined loopback interfaces (lo1) and (lo2).
The show ip command output
HP Switch# show ip IP Routing : Enabled Default Gateway : 15.255.128.1 Default TTL : 64 Arp Age : 20 Domain Suffix : DNS server : | Proxy ARP VLAN | IP Config IP Address Subnet Mask Std Local ---------------- + ---------- --------------- -------------- ---------- DEFAULT_VLAN | Manual 10.0.8.121 255.255.0.0 No No VLAN2 Manual 192.168.12.1 255.255.255.0 No No VLAN3 Disabled Loopback Addresses Loopback IP Config IP Address Subnet Mask -------- ---------- ------------------ --------------- lol Manual 172.16.110.2 255.255.255.255 lo2 Manual 172.16.112.2 255.255.255.255 lo2 Manual 172.16.114.1 255.255.255.255
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NOTE: The default loopback interface ( |
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To display the loopback interfaces configured on the switch in a list of IP routing entries displayed according to destination IP address, enter the show ip route command.
The following example displays the configuration of the default loopback interface (lo0) and one user-defined loopback interface (lo2).
The show ip route command output
HP Switch# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist. ------------------ --------------- ---- --------- ---------- --------- ---- 10.0.0.0/16 DEFAULT_VLAN 1 connected 1 0 127.0.0.0/8 reject static 0 0 127.0.0.1/32 lo0 connected 1 0 172.16.10.121/32 lo2 static 1 0 172.16.100.0/24 10.0.8.11 1 ospf IntraArea 1 1 172.16.102.0/24 VLAN2 2 connected 1 0