Chapter 6 Configuring the Internet Protocol

Configuring an IP Route

The following running-configuration example shows the results of entering the commands in Table 6-1.

!*************************** GLOBAL ***************************

ip no-implicit-service ip redundancy

ip subnet-broadcast

ip route 192.168.0.0/16 192.167.1.1 1

Configuring an IP Route

A static route consists of a destination network address and mask, as well as the next hop to reach the destination. You can also specify a default static route (using

0.0.0.0as the destination network address and a valid next hop address) to direct frames for which no other destination is listed in the routing table. Default static routes are useful for forwarding otherwise unrouteable packets by the CSS.

When you configure a static route, the CSS creates an internal service that periodically polls the configured next hop address with an ICMP echo (or ping) keepalive. The internal service is called an implicit service. If the router fails, the CSS removes any entries from the routing table that point to the failed router and stops sending network traffic to the failed router. When the router recovers, the CSS:

Becomes aware of the router

Reenters applicable routes into the routing table

The implicit service does not determine if the default or static route appears in the routing table. This decision is based on the CSS having a viable ARP entry for the next hop router IP address so the CSS can forward traffic to that destination. The CSS uses the ICMP keepalive as a means to ensure the next hop router MAC address is available and current. However, in certain situations, the next hop router may block ICMP message transmitted by the CSS, which results in a failed ICMP keepalive (the ICMP keepalive is in the Down state). As long as the CSS has the ARP entry of the next hop router the static route is still placed in the routing table.

Note The CSS allows you to disable the internal ICMP keepalive through the ip-no-implicit service command. In this case, if the MAC address for the next hop is not known to the CSS the address will not appear in the routing table.

 

 

Cisco Content Services Switch Routing and Bridging Configuration Guide

 

 

 

 

 

 

OL-4580-01

 

 

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Cisco Systems OL-4580-01 manual Configuring an IP Route