Rib-failure BGP

On November 20, 2009, in CCIE, by Darren

Sometimes when configuring BGP you’ll come accross routes that show rib-failure. What exactly does this mean?

Have a look at this output:

R3#sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
r> 172.16.220.0/24  172.16.220.1        0             0 3 i
*> 192.68.0.0/16    172.16.220.1        0             0 3 {2,1} i
*> 192.68.10.0      172.16.220.1                      0 3 2 i

172.16.220.0/24 is showing up as r> – but what exactly is going on? There is a command you can use to see what’s happened: show ip bgp rib-failure

R3#sh ip bgp rib-failure
Network            Next Hop                      RIB-failure   RIB-NH Matches
172.16.220.0/24    172.16.220.1        Higher admin distance              n/a

Here it’s telling me that the BGP could not be injected into the routing table as there is already a route with a higher administrative distance there. This is proved with the ip routing table:

R3#sh ip route 172.16.220.0
Routing entry for 172.16.220.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet0/1
      Route metric is 0, traffic share count is 1

Essentially a RIB-failure is a note letting you know that the route is in BGP, but it has not been injected into the IP routing table even though it is a valid and best route

(25 April 2012) – Note that rib failure prefixes are still advertised to BGP neighbours. This is not like EIGRP and RIP who will not. You can however prevent BGP from advertising rib-failure routes by configuring bgp suppress-inactive under the BGP process.

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BGP Lab 11

On November 20, 2009, in CCIE, Dynamips, by Darren

Topology used is over here: http://mellowd.co.uk/ccie/?p=243

BGP Lab 11:

  • All routers are peered via BGP
  • Router9 has the network 24.83.176.1/24 attached via a loopback
  • Router2 has the network 24.83.177.1/24 attached via a loopback
  • All networks MUST be inserted into the BGP process
  • Now ensure that Router8 and Router1 see the full aggregate of 24.83.176/23 advertised. More specific routes MUST be supressed. i.e. Router1 and Router8 should have the aggregate ONLY – Do this WITHOUT removing any of the networks from the BGP process
  • Now change the configuration so that Router1 and Router8 get the aggregate as well as the more specific routes, however using a community tag (on Router2), ensure that Router1 does NOT advertise the more specific routes to Router6.
  • Router6 should still get the aggregate route
  • Check to make sure Router1 has all the routes and Router6 ONLY has the aggregate route

Click on the thumbnail for the full topology:

BGP 11 150x150 BGP Lab 11

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BGP Lab 10

On November 20, 2009, in CCIE, Dynamips, by Darren

Topology used is over here: http://mellowd.co.uk/ccie/?p=243

BGP Lab 10:

  • CompanyA is a customer of ISP1
  • CompanyA is peered with CompanyB which is NOT a customer of ISP1
  • ISP1 advertises the loopbacks of both Router8 and Router9, however wants to ensure that only it’s own customers know about 8.8.8.8
  • ISP1 does not care that all routers know about 9.9.9.9
  • ISP1 does not trust CustomerA to put the right measure in place, so you need to do it from the ISP1 side.
  • In other words, make sure that CompanyA knows about 8.8.8.8 but force it not to advertise that route any further

Click on the thumbnail for the full topology:

BGP 10 150x150 BGP Lab 10


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BGP Lab 9

On November 20, 2009, in CCIE, Dynamips, by Darren

Topology used is over here: http://mellowd.co.uk/ccie/?p=243

BGP Lab 9:

  • ISP1 is running OSPF internally so that all loopbacks are accessible
  • Router1 has the network 172.20.1.0/24 attached to it (via a loopback)
  • Router8 has the network 172.20.8.0/24 attached to it (via a loopback)
  • Ensure both these networks are advertised by both Router1 and Router8
  • ISP1 contains the entire 172.20.0.0/16 network. Ensure this aggregate is always advertised out, no matter the condition of the more granular networks
  • Using MED, ensure traffic from Router10 to 172.20.1.0/24 goes via Router2 and traffic to 172.20.8.0/24 goes via Router9
  • Ensure the MED comes from the OSPF metric itself

Click on the thumbnail for the full topology:

BGP 9 150x150 BGP Lab 9

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BGP Lab 8

On November 20, 2009, in CCIE, Dynamips, by Darren

Topology used is over here: http://mellowd.co.uk/ccie/?p=243

BGP Lab 8:

  • Address as normal in the topology – Add the loopback of 99.99.99.99 and 22.22.22.22 to Router’s 9 and 2 respectively
  • All routers are peered via BGP with OSPF running as well
  • Use a filter on AS500 to ensure it is non-transit
  • Company1 now wants to prepend it’s AS number 3 times for any route sent off to Customer2
  • Allow Customer3 to transit through ISP1
  • Ensure Customer3′s Private-AS number is stripped off before advertising it out
  • Allow Company1 and Company2 to get to Customer3

Click on the thumbnail for the full topology:

BGP 81 150x150 BGP Lab 8

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