BGP route advertisement Issue

thiyagarajankalaiselvan · ‎08-06-2013

Hello All,

I'm working on with a task to break the existing 10.0.0.0/24 into 10.0.0.0/25 and 10.0.0.128/25 and I have to advertise the individual circuits over the WAN circuits. Currently we are advertising 10.0.0.0/24 and my requirement is:

1- We have to advertise the 10.0.0.0/25 and 10.0.0.128/25 over the WAN circuit.

2- The subnet 10.0.0.0/25 over the primary circuit and 10.0.0.128/25 over the secondary circuit.

I have tried to implement the above two requirement and the indvidual subnets were not advertsing over the WAN circuit.

While troubleshooting I'm finding there is no route to the desitnation but there is route in the routing table. Please find below the logs:

Please help me to decode the below and to execute my requirement.

*Mar 1 00:53:20.615: BGP: Applying map to find origin for 10.0.0.0/25
*Mar 1 00:53:20.615: BGP: Applying map to find origin for 10.0.0.128/25
*Mar 1 00:53:20.619: BGP(0): no valid path for 10.0.0.0/25
*Mar 1 00:53:20.619: BGP(0): no valid path for 10.0.0.128/25

R1#sh ip route 10.0.0.0
Routing entry for 10.0.0.0/8, 3 known subnets
Attached (1 connections)
Variably subnetted with 2 masks

S       10.0.0.0/25 [1/0] via 10.0.0.2
C       10.0.0.0/24 is directly connected, Serial0/0
S       10.0.0.128/25 [1/0] via 10.0.0.2

R1#sh ip bgp
BGP table version is 11, local router ID is 30.0.0.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
* 10.0.0.0/25      10.0.0.2                 0         32768 i
* 10.0.0.128/25    10.0.0.2                 0         32768 i
R1#

Regards,

Thiyagu

ctejeiro · ‎08-06-2013

Hi,

it seems you don´t have a valid route for the next-hop 10.0.0.2

Instead of next-hop 10.0.0.2 why don´t you just configure null0 interface???

ip route 10.0.0.0 255.255.255.128 null0

ip route 10.0.0.128 255.255.255.128 null0

Regards

Richard Burts · ‎08-06-2013

In this case I believe that it would have negative impact to use the null routes as you suggest. Notice that 10.0.0.0/24 is directly connected on the serial interface. If there are more specific routes configured with null 0 as the next hop then all traffic that should be sent out the serial interface will be forwarded to null 0 and discarded.

I also observe that if the static routes do show up in the output of show ip route then the next hop is considered to be reachable by IOS. If the next hop is not reachable then the static route is not inserted into the routing table.

Given that the routes do show up in the output of show ip route and do show up in the output of show ip bgp it seems to me that BGP is ok with them. The log messages just before the error indicate that BGP is applying a map to find the origin. I wonder what is in that map and whether the BGP is more related to the content of the map than it is about the validity of the routes.

HTH

Rick

HTH

Rick

ctejeiro · ‎08-06-2013

Yes, sorry. In this case more as we have specific static routes with next-hop null0 interfaces will discard traffic...

Could we have the bgp related configuration?

"Conditional BGP Route Injection" functionality is used to inject more specific routes and I think it could be helpful here.

http://www.cisco.com/en/US/partner/docs/ios-xml/ios/iproute_bgp/configuration/15-mt/irg-basic-net.html#GUID-1F8A535C-8D64-4B78-8EFF-D35D36074563