eBGP - no default route

Unanswered Question
Sep 13th, 2010


Recently, after our provider made a switchover of their router, our router's eBGP session is not receiving anymore the default route in which it forced me to define the static default route for us to reach the Internet.

I tried shutting down the serial Interface and bringing it back up again but to no avail. I also tried removing the serial's PPP encapsulation but still to no avail. I also tried removing my eBGP neighbor and reconfigured it back but still to no avail.

#sh ip bgp neighbors <my_neighbor_ip> routes

Total number of prefixes 0

#sh ip bgp neighbors <my_neighbor_ip> received-routes

Total number of prefixes 0

Below is my eBGP configuration for my neighbor:

neighbor <my_neighbor_ip> remote-as <my_neighbor_AS>
neighbor <my_neighbor_ip> description eBGP to France Telecom
neighbor <my_neighbor_ip> default-originate
neighbor <my_neighbor_ip> soft-reconfiguration inbound
neighbor <my_neighbor_ip> prefix-list announce out
neighbor <my_neighbor_ip> route-map default-IN in
neighbor <my_neighbor_ip> route-map localOnly out
neighbor <my_neighbor_ip> maximum-prefix 250000 70

ip as-path access-list 5 permit ^$
ip prefix-list announce description Prefix Announcements
ip prefix-list announce seq 5 permit xxx.xxx.xxx.xxx/22 le 24
ip prefix-list announce seq 15 deny le 32
ip prefix-list default-in seq 5 permit

route-map default-IN permit 10
match ip address prefix-list default-in
route-map localOnly permit 5
match as-path 5

Am I missing something here? This was working well and then apparently just broke off after the switchover considering that I did not change anything in my configuration which is perfectly working before.

Your comments and suggestions are highly appreciated.



I have this problem too.
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marikakis Mon, 09/13/2010 - 23:39

If you don't have any other problems reaching the internet when you configure a static default on your side and your BGP session is established and stable, then the problem is not due to serial interface issues or interface encapsulation.

I don't see a problem with the BGP configuration on your side. Your prefixes are being announced by the ISP if you can communicate with remote hosts on the Internet (using a static default on your side). Your incoming filters aren't blocking the default. The output of "sh ip bgp neigh .... received-routes" shows you are not receiving the default from the ISP (which is before any incoming filters are applied on your side anyway).

Since you have removed the BGP config and have put it back, the BGP session has also been reset. It looks like the ISP is not sending you the default due to the BGP configuration on their side, e.g. because of their outgoing filters or lack of "default-originate" command towards your router (might have been forgotten when they made changes on their side in the first place). (BTW: You have the "default-originate" command on your side and your outgoing filter is blocking the default. Is there a reason why you have this command?)

As Laurent suggested, you need to contact your ISP about this.

ashok_boin Tue, 09/14/2010 - 02:11

Hi Joey,

It's absolutely problem with ISP end configuration. Please ask them to provide "sh ip bg advertised-routes".

And, as mentioned by Marik in earlier post, the command "neighbor xxxx default-originate" is not necessary at your router and may lead to routing loops. Anyhow, ISPs would take care of accepting with specific filters inbound from customers but there is no reason to have this command at your end.



jesquibal Tue, 09/14/2010 - 02:48

Thank you all for your comments and suggestions.

Below is the result of the advertised-routes from my ISP. Does the result below clearly means that their BGP config is missing "default-originate" ?

#sh ip bgp neighbors xxx.xxx.xxx.xxx advertised-routes
BGP table version is 851321, local router ID is xxx.xxx.xxx.xxx
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Originating default network  
  Network          Next Hop            Metric LocPrf Weight Path
  Total number of prefixes 0

Ashok/Marikakis, thank you also for commenting about "default-originate". I am going to remove this.

Thank you again in advanced for your kind help.

marikakis Tue, 09/14/2010 - 03:12

Output shows "Originating default network", so this means they are originating it (now). Can you check again if you are receiving it on your side now?

jesquibal Tue, 09/14/2010 - 03:45

I e-mailed by ISP asking them about "default-originate" and outgoing filters and it suddenly worked!

Thanks much everyone! Your comments and suggestions/recommendations are very well appreciated!



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