headers
Matys Łukasz | 1 Apr 2010 12:43

[quagga-users 11441] Re: ibgp only a few routes annonced

bobby16093 <at> netcourrier.com pisze:
> Hi,
> 
> I'm using Quagga on 2 routers and 2 transit with full BGP, running iBPG 
> between them, with next-hop-self. Router A does advertise all its 
> 300.000 routes to B which see them. Router B should advertise 300.000 
> routes as well to router A, but it doesn't, it only advertise 37600 
> routes, so of course router A does only see 37600 routes. So I'm quite 
> sure there's on problem on router B, but its config is nearly identical 
> to routerA, so I really don't know what the problem can be...
> 
> Any idea ?
> 
> Thanks in advance  !
> 
> Bobby
> 
> 
> This is my config on router B :
> 
> # external transit
>  neighbor x.x.x.x remote-as xxxxx
>  neighbor x.x.x.x soft-reconfiguration inbound
>  neighbor x.x.x.x prefix-list outfilter out
>  neighbor x.x.x.x route-map OperatorB in
>  neighbor x.x.x.x filter-list 10 out
> 
> #internal bgp
>  neighbor y.y.y.y remote-as yyyyy
>  neighbor y.y.y.y next-hop-self
(Continue reading)

Permalink | Reply |
headers
Bobby | 1 Apr 2010 14:12
Favicon

[quagga-users 11442] Re: ibgp only a few routes annonced

Thanks for your answer !

 > If router A has better paths(the same) than paths from B(for example
 > local preference)...

Are you sure ? How could router A compare paths as it doesn't even 
receive them ? And I verified, there's only 37600 routes on "show nei A 
advertised-routes" on router B.

 > then it will not get the same paths using iBGP. Try
 > to shut down ip transit session at A, then it will get paths from B.

I cleared both transit session (soft), without changes.

Regards,

Bobby
Permalink | Reply |
headers
Barry Friedman | 1 Apr 2010 19:54
Picon
Favicon

[quagga-users 11443] Re: ibgp only a few routes annonced

On Thu, Apr 1, 2010 at 5:12 AM, Bobby <bobby16093@...> wrote:
> Thanks for your answer !
>
>> If router A has better paths(the same) than paths from B(for example
>> local preference)...
>
> Are you sure ? How could router A compare paths as it doesn't even receive
> them ? And I verified, there's only 37600 routes on "show nei A
> advertised-routes" on router B.

If B prefers the iBGP path from A to its own received eBGP path (due
to localpref, as-path, etc), then it will not advertise that path back
to A (split horizon). If B did previously advertise the route it will
withdraw it.

Simple way to check is look 'show ip bgp x.x.x.x' for one of the
routes B did not advertise and see if the path from A is marked as
best. B will not advertise such a route back to A.

>
>> then it will not get the same paths using iBGP. Try
>> to shut down ip transit session at A, then it will get paths from B.
>
> I cleared both transit session (soft), without changes.

I think the suggestion was to shut down the transit peering session
(ie. neighbor x.x.x.x shutdown) on A to see if that causes B to
advertise the full set to A. Soft clear would just cause a
re-advertisement of the routes and would not change anything, assuming
best path selection is deterministic.
(Continue reading)

Permalink | Reply |
headers
Bobby | 1 Apr 2010 22:09
Favicon

[quagga-users 11444] Re: ibgp only a few routes annonced

Barry Friedman wrote :
 > If B prefers the iBGP path from A to its own received eBGP path (due
 > to localpref, as-path, etc), then it will not advertise that path back
 > to A (split horizon). If B did previously advertise the route it will
 > withdraw it.
 >
 > Simple way to check is look 'show ip bgp x.x.x.x' for one of the
 > routes B did not advertise and see if the path from A is marked as
 > best. B will not advertise such a route back to A.

Yes, you're certainly right. As we are using a near-Tier1 provider and a 
smaller provider, the router B connected to this second provider 
announced so few routes to router A that I thought it was a malfunction, 
but their routes are just longer and not announced to router A then.

 >>> then it will not get the same paths using iBGP. Try
 >>> to shut down ip transit session at A, then it will get paths from B.
 >> I cleared both transit session (soft), without changes.
 >
 >
 > I think the suggestion was to shut down the transit peering session
 > (ie. neighbor x.x.x.x shutdown) on A to see if that causes B to
 > advertise the full set to A. Soft clear would just cause a
 > re-advertisement of the routes and would not change anything, assuming
 > best path selection is deterministic.

OK, I understand now.

Thanks to you and Matys !
(Continue reading)

Permalink | Reply |
headers
Matys Łukasz | 2 Apr 2010 10:58

[quagga-users 11446] Re: ibgp only a few routes annonced

Bobby pisze:
> Barry Friedman wrote :
>  > If B prefers the iBGP path from A to its own received eBGP path (due
>  > to localpref, as-path, etc), then it will not advertise that path back
>  > to A (split horizon). If B did previously advertise the route it will
>  > withdraw it.
>  >
>  > Simple way to check is look 'show ip bgp x.x.x.x' for one of the
>  > routes B did not advertise and see if the path from A is marked as
>  > best. B will not advertise such a route back to A.
> 
> Yes, you're certainly right. As we are using a near-Tier1 provider and a 
> smaller provider, the router B connected to this second provider 
> announced so few routes to router A that I thought it was a malfunction, 
> but their routes are just longer and not announced to router A then.
> 
>  >>> then it will not get the same paths using iBGP. Try
>  >>> to shut down ip transit session at A, then it will get paths from B.
>  >> I cleared both transit session (soft), without changes.
>  >
>  >
>  > I think the suggestion was to shut down the transit peering session
>  > (ie. neighbor x.x.x.x shutdown) on A to see if that causes B to
>  > advertise the full set to A. Soft clear would just cause a
>  > re-advertisement of the routes and would not change anything, assuming
>  > best path selection is deterministic.
> 
> OK, I understand now.
> 
> Thanks to you and Matys !
(Continue reading)

Permalink | Reply |

Gmane