Configuring Conditional Advertisement

Unanswered Question
Oct 22nd, 2009
User Badges:

We need to configure conditional advertisement between two routers running BGP v4. This will enable us to make two ISPs back up to each other.


However we configured two ISPs in two different routers. Do we need a ibgp between routers?


Diagram is duly attached.


We have tried the configuration in our lab, the confirguration is attached with GNS.txt file name.

Unfortunately the configuration did not work for us. we are able to get iBGP routes but it doesnot announce the second prefix when the first ISP is down.




Attachment: 
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
slmansfield Thu, 10/22/2009 - 09:47
User Badges:
  • Silver, 250 points or more

I don't see the attachment of your GNS.txt file. Could you include that? thx

navinder.singh Thu, 10/22/2009 - 10:18
User Badges:

Thank you!!!


I am unable to attache the file, however, it is the same as attached the Net1.gif file, in which 2 routers were configured as ISPs and 2 were ibgp routers.

Giuseppe Larosa Thu, 10/22/2009 - 10:14
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Navinder,


>> However we configured two ISPs in two different routers. Do we need a ibgp between routers?


generally speaking in a scenario like yours the answer is yes.


second router has to receive BGP routes from router1 however, also router1 receives routes from router2 so an iBGP session is needed but it might not be enough.


post your current config.


there is an attach file options when you create a new post


Hope to help

Giuseppe


slmansfield Thu, 10/22/2009 - 11:09
User Badges:
  • Silver, 250 points or more

After reviewing the diagram (which I'm having a hard time reading, so I apologize if I am mis-interpretting something), it looks like the outbound traffic is directed via HSRP between the two gateways, GW1 and GW2.


If you want to manage inbound traffic so it takes a preferred path through one ISP and fails over to the other ISP, I think you could just configure a prepended AS path for the network(s) you are advertising to the Internet over the less preferred ISP path. I don't think you need to make GW1 and GW2 IBGP peers to accomplish this.

navinder.singh Thu, 10/22/2009 - 19:33
User Badges:

Thanks Giuseppe!!


Please find the configuration below


router bgp 24471


no synchronization


bgp log-neighbor-changes


network 203.99.41.0


network 203.99.42.0


neighbor 202.88.238.65 remote-as 17465


neighbor 202.88.238.65 ebgp-multihop 5


neighbor 202.88.238.65 update-source Loopback0


neighbor 202.88.238.65 soft-reconfiguration inbound


neighbor 202.88.238.65 route-map ustr_in in


neighbor 202.88.238.65 route-map ustr_out out


neighbor 202.88.238.65 advertise-map ISP2_out non-exist-map ISP2_down


neighbor 203.99.41.65 remote-as 24471


neighbor 203.99.41.65 update-source Loopback0


neighbor 203.99.41.65 next-hop-self


neighbor 203.99.41.65 soft-reconfiguration inbound


no auto-summary



ip as-path access-list 100 permit ^17465_[0-9]*$


!


!


ip prefix-list ISP2_in seq 5 permit 59.144.4.0/24


!


ip prefix-list ustr seq 10 permit 203.99.40.0/21


!


ip prefix-list ustr1 seq 5 permit 203.99.40.0/24


!


ip prefix-list ustr2 seq 5 permit 203.99.41.0/24


!


ip prefix-list ustr3 seq 5 permit 203.99.42.0/24



route-map ustr_out permit 10


match ip address prefix-list ustr3


!


route-map ISP2_down permit 10


match ip address prefix-list ISP2_in


!


route-map ISP2_out permit 10


match ip address prefix-list ustr2


!


route-map ustr_in permit 10


match ip address 100




slmansfield Mon, 10/26/2009 - 11:32
User Badges:
  • Silver, 250 points or more

I think the issue preventing the conditional advertisement from working is the route-map to the same neighbor. That route-map is only advertising 203.99.42.0/24. When the watched route is lost, this route-map still only allows the advertisment of 203.99.42.0/24.


If you either remove the route-map or adjust it to include 203.99.41.0/24 you will find that the conditional advertisement works.


Actions

This Discussion