Configuring a black hole static route

About this task

Configure a black hole static route to the destination a router advertises to avoid routing loops after the router aggregates or injects routes to other routers.

If a black hole route is enabled, you must first delete or disable it before you can add a regular static route to that destination.

Procedure

Enter either Global Configuration mode or VRF Router Configuration mode for a specific VRF context:

enable

configure terminal

Optional: router vrf WORD<1-16>
Create a black hole static route:

ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 weight <1–65535>
Enable a black hole static route:

ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 enable [next-hop-vrf WORD<0-16>]
Configure other black hole static route parameters as required.

When you specify a route preference, appropriately configure the preference so that when the black-hole route is used, it is elected as the best route.

Example

Create a black hole static route and enable the black hole static route.

Switch:1>enable
Switch:1#configure terminal
Switch:1(config)#ip route 192.0.2.0 255.255.0.0 255.255.255.255 weight 200
Switch:1(config)#ip route 192.0.2.0 255.255.0.0 255.255.255.255 enable

Variable definitions

Use the data in the following table to use the ip route command.

Table 1. Variable definitions
Variable	Value
`<A.B.C.D>`	The first and second `<A.B.C.D>` specify the IP address and mask for the route destination. 255.255.255.255 is the destination of the black hole route.
enable	Adds a static route to the router or VRF. The no form of this command is `no ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 enable`.
local-next-hop enable	Enables the local next hop for this static route. The default form of this command is `default ip route <A.B.C.D> <A.B.C.D> <A.B.C.D> local-next-hop enable`. The no form of this command is `no ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 local-next-hop enable`.
next-hop-vrf `WORD<0-16>`	Specifies the next-hop VRF instance by name. The default form of this command is `default ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 next-hop-vrf <WORD 0-16>`. The no form of this command is `no ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 next-hop-vrf <WORD 0-16>`.
weight `<1-65535>`	Specifies the static route cost. The default form of this command is `default ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 weight`. Note: Do not configure a static interface subnet route with a weight of 1.
preference `<1-255>`	Specifies the route preference. The default form of this command is `default ip route <A.B.C.D> <A.B.C.D> 255.255.255.255 preference`.