Virtual Loopback Interface Overview - Cisco 6000 Series Configuration Manual

Interface and hardware component configuration guide for cisconcs 6000 series routers, ios xr release 6.4.x
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Virtual Loopback Interface Overview

Virtual Loopback Interface Overview
A virtual loopback interface is a virtual interface with a single endpoint that is always up. Any packet transmitted
over a virtual loopback interface is immediately received by the selfsame interface. Loopback interfaces
emulate a physical interface.
In Cisco IOS XR software,virtual loopback interfaces perform the following functions:
• Loopback interfaces can act as a termination address for routing protocol sessions. This allows routing
• You can ping the loopback interface to verify that the router IP stack is working properly.
In applications where other routers or access servers attempt to reach a virtual loopback interface, you must
configure a routing protocol to distribute the subnet assigned to the loopback address.
Packets routed to the loopback interface are rerouted back to the router or access server and processed locally.
IP packets routed out the loopback interface but not destined to the loopback interface are dropped. Under
these two conditions, the loopback interface can behave like a null interface.
Null Interface Overview
A null interface functions similarly to the null devices available on most operating systems. This interface is
always up and can never forward or receive traffic; encapsulation always fails. The null interface provides an
alternative method of filtering traffic. You can avoid the overhead involved with using access lists by directing
undesired network traffic to the null interface.
The Null 0 interface can be displayed with the show interfaces null0 command.
Virtual Management Interface Overview
Configuring an IPv4 virtual address enables you to access the router from a single virtual address with a
management network without prior knowledge of which RP is active. An IPv4 virtual address persists across
route processor (RP) switchover situations. For this to happen, the virtual IPv4 address must share a common
IPv4 subnet with a management Ethernet interface on both RPs.
On a Cisco NCS 6000 Series Router where each RP has multiple management Ethernet interfaces, the virtual
IPv4 address maps to the management Ethernet interface on the active RP that shares the same IP subnet.
Active and Standby RPs and Virtual Interface Configuration
The standby RP is available and in a state in which it can take over the work from the active RP should that
prove necessary. Conditions that necessitate the standby RP to become the active RP and assume the active
RP's duties include:
• Failure detection by a watchdog
• Administrative command to take over
• Removal of the active RP from the chassis
If a second RP is not present in the chassis while the first is in operation, a second RP may be inserted and
automatically becomes the standby RP. The standby RP may also be removed from the chassis with no effect
on the system other than loss of RP redundancy.
Interface and Hardware Component Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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protocol sessions to stay up even if the outbound interface is down.
Configuring Virtual Loopback and Null Interfaces

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