Configuring a static IP route

Static route

Configure a static route to a specific network or host address

Null route

Configure a "null" route to discard IP traffic to a specific network or host address:
  • Discard traffic for the destination, with ICMP notification to sender

  • Discard traffic for the destination, without ICMP notification to sender

Syntax:


ip route <dest-ip-addr>/<mask-length> <next-hop-ip-addr|vlan <vlan-id>|reject|blackhole> [metric <metric>] [distance <1-255>] [tag-value <tagval>]

no ip route <dest-ip-addr>/<mask-length> <next-hop-ip-addr|vlan <vlan-id>|reject|blackhole> [metric <metric>] [distance <1-255>] [tag-value <tagval>]

Allows the addition and deletion of static routing table entries. A route entry is identified by a destination (IP address/mask length) and next-hop pair. The next-hop can be either a gateway IP address, a VLAN, or the keyword "reject" or "blackhole".

A gateway IP address does not have to be directly reachable on one of the local subnets. If the gateway address is not directly reachable, the route is added to the routing table as soon as a route to the gateway address is learned.

<dest-ip-addr>/<mask-bits>

The route destination and network mask length for the destination IP address. Alternatively, you can enter the mask itself. For example, you can enter either 10.0.0.0/24 or 10.0.0.0 255.255.255.0 for a route destination of 10.0.0.0 255.255.255.0.

next-hop-ip-addr

This IP address is the gateway for reaching the destination. The next-hop IP address is not required to be directly reachable on a local subnet. (If the next-hop IP address is not directly reachable, the route will be added to the routing table as soon as a route to this address is learned.)

reject

Specifies a null route where IP traffic for the specified destination is discarded and an ICMP error notification is returned to the sender.

blackhole

Specifies a null route where IP traffic for the specified destination is discarded and no ICMP error notification is returned to the sender.

metric

Specifies an integer value that is associated with the route. It is used to compare a static route to routes in the IP route table from other sources to the same destination.

distance

Specifies the administrative distance to associate with a static route. If not specified, this value is set to a default of 1. (Range: 1 to 255)

tag

Specifies a unique integer value for a given ECMP set (destination, metric, distance.)

The no form of the command deletes the specified route for the specified destination next-hop pair.

The following example configures two static routes for traffic delivery and identifies two other null routes for which traffic should be discarded instead of forwarded.

Configuring static routes

switch(config)# ip route 10.10.40.0/24 10.10.10.1 1

switch(config)# ip route 10.10.50.128/27 10.10.10.1

switch(config)# ip route 10.10.20.177/32 reject2

switch(config)# ip route 10.10.30.0/24 blackhole3 
1 Configures static routes to two different network destinations using the same next-hop router IP address.

2 Configures a null route to drop traffic for the device at 10.50.10.177 and return an ICMP notification to the sender.

3 Configures a null route to drop traffic for the 10.50.10.0 network without any ICMP notification to the sender.