Chasing routes in the network
Have you ever tried to find out why the dynamic routing protocol in your network is not passing specific prefix as expected? And the situation had not improved even though ad-hoc static routes were created here and there? Networking protocols are designed to be simple in general. However, they can create very complex state machine systems that may be very hard to diagnose router by router.
What to do when the destination router is positively redistributing the route to the network but the source router does not have a clue about it? Each router should be analyzed one by one and assessed with following topics:
- Is the router peering correctly with his neighbors? Is the peering stable? Are the timers and other neighbor parameters aligned?
- Is the route being passed to its neighbor? Is it making through up to the routing table?
- Is there route redistribution among routing protocols? Has the route been correctly redistributed?
- Is there route summarization in place? Has the route been correctly summarized (and the original route filtered)?
This involves checking the configuration and state information from all routers on all possible paths over the network. Outputs from neighbors must be compared to locate where the route blackhole has been erroneously created. It usually involves lot of administrative sessions to the router and manual work as the scripts for this task would be too complex to create.
IP Fabric offers a very convenient way to see where the problem may be. Do you have a suspicion that your route is a part of a routing loop? One of the links is constantly going up and down? The outer address of a tunnel is advertised inside the same tunnel? You simply put your troubled route as a filter to Routing stability table.
You can quickly look up any route on any router in the network by the following criteria:
- Classic prefix string (such as “192.168.0.0/16”) or a substring (such as “192.168”)
- Using just the netmask length (such as /0 or /32) — for example, if you are looking for default route or for host routes only
- The IP address of the destination (such as 192.168.0.1) — all prefixes in routing tables will be found in the same way like destination IP routing works (ie. 192.168.0.1/32, 192.168.0.0/24, 192.168.0.0/16 and 0.0.0.0/0 would be displayed in this case if it’s present in the network)
- Route origin (if it is a connected network, static route entry, any type of dynamic routing protocol)
- Next hop value (IP and/or outgoing interface)
All lookups are VRF-aware and return the results in seconds. You will see how many times is the route present in the network and if it recently converged which would indicate instability.
If the route is not flapping, it still may be incorrectly distributed. You simply put your troubled route as a filter to Cumulative network table and you can immediately see which routers know about it and which routers don’t.
You can quickly check the protocols that are used to transport the route (or if the subnet is directly connected or statically routed). Moreover, you can quickly assess all next-hops and trace the path on one screen instead of logging to each router and looking for details manually.
Furthermore, you can have an overall view of all the routing methods (directly connected, static or dynamic) used in your network. Those should match the network design — not desired protocols should be turned off and the desired ones should be up. Even the misconfigured exotic routing protocol left behind from testing can be a source of suboptimal or faulty routing.
IP Fabric can help you approach possible routing problems proactively. It is pointless to have half-open routing peerings or misconfigured neighbors even though it does not affect any network traffic so far. Those should be either repaired or removed from the network. For example table of OSPF, neighborships will quickly show routers where the peerings should be revised because it did not reach the FULL state.
Are you eager to see all of IP Fabric’s powerful features? Schedule a time for a free video call with our expert team who will help create a solution to fit your needs.