Posted on July 27, 2021 6:20 pm
 |  Asked by Pradeep Godhala
 |  78 views
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Hi,

I am trying to clear the route table for a specific prefix on a 7280SR platform running EOS 4.23.3M. But looks like the command isn’t available. Does anyone how to clear the RIB and FIB for a specific prefix on 4.23.3M.??

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Answered on July 28, 2021 5:25 am

Hi Pradeep,

Thanks for reaching out.

There is no command available in EOS to clear the routing table for a particular prefix.

Could you please confirm as to what we are trying to achieve here? By Clearing are we referring to the removal of the route or for the recalculation of the route?

Are we suspecting that the route is stuck in a bad state?

For the removal of the route from the Routing table we can make use of Route-maps and ACLs inorder to block that prefix/route from getting installed in RIB and FIB.

 

Thanks,

Bhavana.

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Posted by Aniket Bhowmick
Answered on July 28, 2021 6:30 am

Hi Pradeep,

With respect to clearing a route, you should first ensure how the route is learnt in the first place.

Let's say the prefix is learnt via static command (ip route 10.1.1.0/24 1.1.1.1), Then in order to clear the route, you need to make sure the static command is itself removed (no ip route 10.1.1.0/24 1.1.1.1).

If the prefix is learnt through some dynamic routing protocol, you need to deny the route using a route-map and prefix-list in order to make sure it is not installed in RIB.

If you have the prefix learnt from two different routing protocol ( say OSPF and BGP which has different AD values), only the prefix learnt via lower AD would be preferred and installed in RIB (in this case- OSPF, as its AD is 110 and BGP is 200).

If you have a prefix learnt using some dynamic protocol (say OSPF), you can also configure a static null route using the command- (ip route 10.1.1.0/24 Null0). After that, the OSPF route would be removed and instead the Null route would be programmed due to lower AD (static route has AD of 1). The null route is basically a blackhole route, so any packet received on the switch with destination IP in the network 10.1.1.0/24 will be dropped (as if the route doesn't even exist and doesn't want to prefer the default route either).

As mentioned by Bhavana earlier, there is no explicit command in EOS to clear a specific route. But ARPs (host routes) can be cleared using the command "clear ip arp <ip-address>".

Let us know if there is any other query.

Regards,

Aniket

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Posted by Naveen Chandra
Answered on July 30, 2021 9:53 am

Hi Pradeep,

 

I believe you are looking for a command to clear the routing table / a specific prefix in the routing table. In EOS such a command is not needed as in EOS the routing table gets updated/refreshed in real time.

 

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