Core Issue
Route redistribution is used to propagate routes that are statically configured or learned through one routing protocol into another routing protocol. However, at times, the static routes might not get redistributed into various protocols or might not get propagated to other routers in the network for any of these reasons:
- Route filters denying routes from being redistributed or propagated
- A metric not configured for the redistributed routes.
- Discontiguous network addressing with a classful routing protocol like Routing Information Protocol version 1 (RIPv1) or Interior Gateway Routing Protocol (IGRP)
- Absence of subnet keyword in the redistribute command when redistributing into Open Shortest Path First (OSPF)
- Misconfiguration of the level into which the static route is redistributed when configuring redistribution into Integrated Intermediate System-to-Intermediate System (ISIS)
- Auto-summarization is enabled when redistributing into Border Gateway Protocol (BGP).
Resolution
If there are any route filters configured while redistributing by issuing the route-map or distribute-list commands, check if they block the static route that is not redistributed or propagated. This is applicable to all the protocols.
All the protocols use a default metric value for a static route being redistributed. However, in earlier versions of Cisco IOS Software, Routing Information Protocol (RIP) and Enhanced Interior Gateway Routing Protocol (EIGRP) may require the metric for the redistributed static route to be configured explicitly by issuing either the default-metric command or using the metric option with the redistribute command in the router configuration mode.
Classful routing protocols like RIPv1 and Interior Gateway Routing Protocol (IGRP) do not advertise the subnet mask for the route. If the static route being redistributed is part of a major network whose subnet is directly connected to another router receiving the update, it results in a discontiguous network situation, and the receiving router ignores the static route being received. The solution is to avoid using discontiguous networks when using a classful routing protocol.
If routes are redistributed into OSPF and the subnet keyword is not used, only classful networks get redistributed. As a result, static routes to subnets do not get redistributed. Using the subnet keyword while redistributing into OSPF resolves this issue.
Routes get redistributed into ISIS as Level 2 (L2) routes only by default. While redistributing into ISIS, Level 1 (L1), L2 or L 1-2 option has to be specified if the route is not redistributed into the intended levels.
When redistribution is configured with BGP, enabling auto-summarization blocks any subnet routes and allows only major network information to be injected. If subnets are to be redistributed, auto-summarization should be disabled by issuing the no auto-summary command under the router configuration mode of BGP.
For related information, refer to these documents:
Type of Route Missing from Routing Table
External routes only
What Can You Not Ping
Cannot ping beyond the NAT router
Internet gateway device cannot ping destination
show ip bgp {network mask}
Prefix/network does not exist
show ip ospf database external {network} {mask}
No output shown
