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aggregate&contributing routes

‎10-06-2019 01:40 AM

Hi folks, 

I'm using aggregate networks to summarize some LAN networks before advertising into BGP.

aggregate: 172.25.0.0/22

 

At the same time I configured as contributing 172.25.1.0/24, 172.25.10.0/24 and 172.25.20.0/24. 

I'm troubleshooting the behaviour of contributing routers and I'm not sure if is being rejected or sent silently to Routing Engine when contributing route are not listed (show route 172.25.0.0 detail).

 

Many thanks,

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Accepted by topic author alfredo.bosca
‎10-06-2019 04:28 AM

Re: aggregate&contributing routes

[ Edited ]
‎10-06-2019 04:07 AM

Hello,

 


@alfredo.bosca wrote:

 

At the same time I configured as contributing 172.25.1.0/24, 172.25.10.0/24 and 172.25.20.0/24. 

I'm troubleshooting the behaviour of contributing routers and I'm not sure if is being rejected or sent silently to Routing Engine when contributing route are not listed (show route 172.25.0.0 detail).

 

 


 

I presume You configured policy matching only on 172.25.1.0/24, 172.25.10.0/24 and 172.25.20.0/24 , and attached this policy to Your aggregate.

In this case,  the following happens:

1/ any 1 contributing route out of three /24 listed above is enough to bring Your /22 aggregate up

2/ contributing route(s) is/are installed together with aggregate in the RIB/FIB, and are NOT suppressed

3/ any other route that is covered by aggregate (i.e. 172.25.0.0/24 is covered by  172.25.0.0/22) does not bring aggregate up but it is installed in the RIB/FIB.

 

I am not sure though what do You mean by "sent silently to the Routing Engine" - all routes/prefixes pass through the RE on its way from dynamic routing protocol or configuration (i.e. static|agggregate|generate) towards forwarding plane.

If You meant that packets destined to the 172.25.0.0/24 are punted to the RE then no, not by default.

The 172.25.0.0/24 will be installed in the RIB/FIB as explained above and packets destined to 172.25.0.0/24 will be forwarded their own way.

You can cause that punting if You want to but I guess You'd rather not.

HTH

Thx

Alex

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