The originator of that datagram with an ICMP host unreachable message. That it cannot deliver to its ultimate destination because it knows of no route to the destination address, it replies to Sends an Internet Control Message Protocol (ICMP) protocol unreachable message to the source. With the ipv4 unreachables command, if the software receives a nonbroadcast packet destined for itself that uses a protocol it does not recognize, it The only interface configuration command that you can specify for the null interface is the ipv4 unreachables command. You can avoid the overhead that is involved with using access lists by directing undesired network traffic The null interface provides an alternative method ofįiltering traffic. This interface is always upĪnd can never forward or receive traffic encapsulation always fails. Loopback interface can behave like a null interface.Ī null interface functions similarly to the null devices available on most operating systems. Routed out to the loopback interface but not destined to the loopback interface are dropped. Packets routed to the loopback interface are rerouted back to the router or access server, and processed locally. Reach a virtual loopback interface, you must configure a routing protocol toĭistribute the subnet assigned to the loopback address. In applications where other routers or access servers attempt to You can ping the loopback interface to verify that the router IP This allows routing protocol sessions to stay up even if the Loopback interfaces can act as a termination address for routing In Cisco IOS XR Software, virtual loopback interfaces perform System transmits over a virtual loopback interface is immediately received by the same interface. Active and Standby RPs and Virtual Interface ConfigurationĪ virtual loopback interface is a virtual interface with a single endpoint that is always up or active.To configure virtual interfaces, you must understand the following concepts: Information About Configuring Virtual Interfaces If you suspect a user group assignment is preventing you from using a command,Ĭontact your AAA administrator for assistance. The task IDs that you need for each command. You must be in a user group associated with a task group that includes the proper task IDs. Prerequisites for Configuring Virtual Interfaces Configuration Examples for Virtual Interfaces.Information About Configuring Virtual Interfaces.Prerequisites for Configuring Virtual Interfaces.The configurationĪnd control plane are mirrored onto the standby RP and, in the event of a failover, the virtual interfaces move to the ex-standby,įeature History for Configuring Loopback and Null Interfaces on Cisco IOS XR Software Loopback and null interfaces have their control plane presence on the active route switch processor (RP). String unique such that you can have both Loopback 0 and Null 0. The ID is unique per virtual interface type to make the entire name Virtual interfaces have instead a globally unique numerical ID after their names.Įxamples are Loopback 0, Loopback 1, and Loopback 99999. Virtual interfaces have a global scopeĪnd do not have an associated location. Loopback and null interfaces are considered virtualĪ virtual interface represents a logical packet switching entity within the router. This module describes the configuration of loopback and null interfaces. Configuring Virtual Loopback and Null Interfaces
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