Solved: Help on BGP!!!

nikhil.engineer · ‎03-05-2007

Hi Experts,

I have simulated a lab to learn more on BGP. The scenario is as follows:-

R1-R2-R3

Where R2 and R3 are running IBGP while R1 and R2 are running EGP. I have advertised some routes from R1. These routes are visible on R3 as BGP routes.

Now my problem is I cannot ping the routes adv by R1 from R3. Can any one tell me why is it so? Also please provide some solution.

sundar.palaniappan · ‎03-06-2007

Hi,

The problem is R3 doesn't know how to route to 192.168.10.2/xx on R2. The traffic from R2 makes it to R3 but R3 drops the packets as it doesn't know how to route back to 192.168.10.2. Configure R1 to advertise 192.168.10.2/xx via BGP or other means as you desire.

HTH

Sundar

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IWAN HOOGENDOORN · ‎03-05-2007

can you post the configs ... and/or the routingtables ...

Also try to do a traceroute.

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nikhil.engineer · ‎03-05-2007

i tried traceroute but it doesnt work. i cant send u the configs.

Danilo Dy · ‎03-05-2007

Hi,

Without posting the config, we can't help you much. However, try posting the following output for all rouoters;

show ip bgp summary

show ip bgp neighor

show ip route

show ip bgp

show ip int brief

Jon Marshall · ‎03-06-2007

Hi

As stated by other posters it's difficult to say without seeing the routing tables.

Things to check

1) On R3 what is the next hop IP address for the route learned from R1. If it's IBGP between R2 & R3 then it will be the IP address of R1's interface that connects to R2.

Does R3 know how to get to that IP address. if not on R2 you can use the

neighbor "R3 address" next-hop-self which will tell R3 to get to destination at R1 go to via R2.

2) Does R1 know how to get back to R3. You need to know which interface IP address is used as the source IP address from R3. You can use extended ping to set the IP address. Whichever address you use you must make sure that R1 has a route via R2 bakc to it.

HTH

Jon

nikhil.engineer · ‎03-06-2007

Hi All,

I have attached the necessary outputs int the attached text. Also, there is slight change in the scenario. Now, the connection is as follows:

R3-EBGP-R1-IBGP-R2.

Please provide me solution with proper explanation.

Cheers,

Nikhil

sundar.palaniappan · ‎03-06-2007

Hi,

The problem is R3 doesn't know how to route to 192.168.10.2/xx on R2. The traffic from R2 makes it to R3 but R3 drops the packets as it doesn't know how to route back to 192.168.10.2. Configure R1 to advertise 192.168.10.2/xx via BGP or other means as you desire.

HTH

Sundar

nikhil.engineer · ‎03-06-2007

Hi Sundar,

Thanks for your help. I have adv the route in BGP in R1. I am able to ping from R2.

Also if i give a static route from R3 to R2 it will work i suppose.

Pls reply back.

Thanks alot for the explanation it was very helpful.It cleared all my doubts.

Cheers,

Nikhil

sundar.palaniappan · ‎03-06-2007

Nikhil,

Adding a static route on R3 would work as well. It doesn't matter whether the route is a BGP, static or learnt from another source and the only criteria is the routing has to be end-to-end.

I know BGP can be challenging but it's very interesting and I am sure you will have lot of fun with it:)

Good Luck!!

HTH

Sundar