Mailing List Archive: nsp: juniper

Route redistribution

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cynthia_dal at yahoo

May 22, 2012, 12:24 PM

Post #1 of 6 (481 views)
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Route redistribution

Network connections:

We have router A(M120, 10.4), B(MX240, 11.4) and C(M7i, 10.4) connected as a triangle. Router A and B are in OSPF area 0 and also run IBGP between them. Router C is connected to A and B via OSPF area 5.

Problem:

Router A has a lot of EBGP learned routes. These routes are redistributed to router B using IBGP and OSPF. My intension is to redistribute these routes to Router C with OSPF from BOTH A and B. Therefore if A-C link fail, Router C will learn all routes from B. The problem is now Router C only learned these routes from A but can not learn from router B. Did I miss anything or is it Router B not working properly?

Thanks.

Cynthia
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jof at thejof

May 22, 2012, 12:34 PM

Post #2 of 6 (439 views)
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Re: Route redistribution [In reply to]

On Tue, May 22, 2012 at 12:24 PM, Cyn D. <cynthia_dal [at] yahoo> wrote:
> Network connections:
>
> We have router A(M120, 10.4), B(MX240, 11.4) and C(M7i, 10.4) connected as a triangle. Router A and B are in OSPF area 0 and also run IBGP between them. Router C is connected to A and B via OSPF area 5.
>
> Problem:
>
> Router A has a lot of EBGP learned routes. These routes are redistributed to router B using IBGP and OSPF. My intension is to redistribute these routes to Router C with OSPF from BOTH A and B. Therefore if A-C link fail, Router C will learn all routes from B. The problem is now Router C only learned these routes from A but can not learn from router B. Did I miss anything or is it Router B not working properly?

Assuming that B and C are both in the same AS and speaking iBGP, B
wont re-announce the NLRIs back into itself without being set as a
route reflector.

However, I'd recommend making a full-mesh of BGP sessions over
OSPF-learned loopback addresses. Whether that's hauled over MPLS or
some other L2 transport mechanism, or using routing and multi-hop BGP
is up to you.

That way, C will still learn the routes coming into A, even if the
path is via B to get to the next-hops.

Cheers,
jof

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cynthia_dal at yahoo

May 22, 2012, 12:46 PM

Post #3 of 6 (441 views)
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Re: Route redistribution [In reply to]

Thanks for the input. Given our network topology, I am trying to avoid
running a full IBGP mesh.

Also forgot to mention, OSPF Area 5 is a NSSA so that I will have control
over what is being advertised.
----- Original Message -----
From: "Jonathan Lassoff" <jof [at] thejof>
To: "Cyn D." <cynthia_dal [at] yahoo>
Cc: <juniper-nsp [at] puck>
Sent: Tuesday, May 22, 2012 4:34 PM
Subject: Re: [j-nsp] Route redistribution

On Tue, May 22, 2012 at 12:24 PM, Cyn D. <cynthia_dal [at] yahoo> wrote:
> Network connections:
>
> We have router A(M120, 10.4), B(MX240, 11.4) and C(M7i, 10.4) connected as
> a triangle. Router A and B are in OSPF area 0 and also run IBGP between
> them. Router C is connected to A and B via OSPF area 5.
>
> Problem:
>
> Router A has a lot of EBGP learned routes. These routes are redistributed
> to router B using IBGP and OSPF. My intension is to redistribute these
> routes to Router C with OSPF from BOTH A and B. Therefore if A-C link
> fail, Router C will learn all routes from B. The problem is now Router C
> only learned these routes from A but can not learn from router B. Did I
> miss anything or is it Router B not working properly?

Assuming that B and C are both in the same AS and speaking iBGP, B
wont re-announce the NLRIs back into itself without being set as a
route reflector.

However, I'd recommend making a full-mesh of BGP sessions over
OSPF-learned loopback addresses. Whether that's hauled over MPLS or
some other L2 transport mechanism, or using routing and multi-hop BGP
is up to you.

That way, C will still learn the routes coming into A, even if the
path is via B to get to the next-hops.

Cheers,
jof

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juniper-nsp mailing list juniper-nsp [at] puck
https://puck.nether.net/mailman/listinfo/juniper-nsp

pokui at psg

May 22, 2012, 2:58 PM

Post #4 of 6 (441 views)
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Re: Route redistribution [In reply to]

On Tue May 22 22:46:44 2012, Cyn D. wrote:
> Thanks for the input. Given our network topology, I am trying to avoid
> running a full IBGP mesh.

Anything stopping you from making B a BGP route reflector?

> Also forgot to mention, OSPF Area 5 is a NSSA so that I will have
> control over what is being advertised.

The problem still is that with any eBGP route from the Internet
arriving at router A being withdrawn you still have lots of LSA updates
that OSPF has to recalculate.

If you're bent on redistributing you'll have to paste the relevant
configuration on A, B, and C for both the ospf and bgp sections plus
the policies you're using for redistribution.

--
patrick

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jof at thejof

May 22, 2012, 3:12 PM

Post #5 of 6 (438 views)
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Re: Route redistribution [In reply to]

On Tue, May 22, 2012 at 12:46 PM, Cyn D. <cynthia_dal [at] yahoo> wrote:
> Thanks for the input. Given our network topology, I am trying to avoid
> running a full IBGP mesh.

If router C just needs internet transit, perhaps consider just
injecting a default route into your IGP?

It sounds like in this example, that most of the external next-hops
are via A anyway. Perhaps it would be simpler for internal routers to
just use a default, and catch any more-specifics for anything that
doesn't go out A.

--j
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cynthia_dal at yahoo

May 23, 2012, 6:47 AM

Post #6 of 6 (426 views)
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Re: Route redistribution [In reply to]

Thanks for all that replied. Actually this just gets me curious, regardless
of what's the best routing setup, is it even technically doable: to
advertise IBGP and/or OSPF learned routes from router B to router C? I think
it should, but just can't get it to work.

Thanks.

Cyn.
----- Original Message -----
From: "Jonathan Lassoff" <jof [at] thejof>
To: "Cyn D." <cynthia_dal [at] yahoo>
Cc: <juniper-nsp [at] puck>
Sent: Tuesday, May 22, 2012 7:12 PM
Subject: Re: [j-nsp] Route redistribution

> On Tue, May 22, 2012 at 12:46 PM, Cyn D. <cynthia_dal [at] yahoo> wrote:
>> Thanks for the input. Given our network topology, I am trying to avoid
>> running a full IBGP mesh.
>
> If router C just needs internet transit, perhaps consider just
> injecting a default route into your IGP?
>
> It sounds like in this example, that most of the external next-hops
> are via A anyway. Perhaps it would be simpler for internal routers to
> just use a default, and catch any more-specifics for anything that
> doesn't go out A.
>
> --j

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