BGP suppress-inactive

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Apr 1st, 2009
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Hi,


I realised there is a new BGP command in IOS 12.4:

suppress-inactive - Suppress routes that are not in the routing table.

I.e., this commands stops advertising BGP prefixes which failed to be written to the RIB (there is another route available with better AD - static, e.g.).


Do I understand correctly such prefixes were not advertised in previous IOS versions, but they are by default since 12.4?


What about redistribution?

Are the inactive routes redistributed from BGP by default since 12.4., too?


Thanks,

Milan

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Edison Ortiz Wed, 04/01/2009 - 14:35
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Milan,


That command has been around for quite some time. Not sure where you got that information about being new to 12.4


http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp1.html#wp1014705


BTW, inactive routes are the ones listed with r> in the BGP table due to RIB failure.


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milan.kulik Wed, 04/01/2009 - 14:56
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Hi Edison,


yes, you are correct, I noticed 12.2(8) router behaving strange way.

Then I realised a difference comparing with a 12.4 router.


So the command is available since 12.2(11)T.


I know the inactive routes are that with r>.


But still my understaing is:

In the past (before this command introduced) the inactive routes were not advertised, but current IOS is advertising them by default?


And I'm not sure regarding redistribution.


Thanks,

Milan

Edison Ortiz Wed, 04/01/2009 - 15:07
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My understanding is that RIB failure routes were advertised in previous IOSes and this command provides the ability NOT to advertise those routes if needs be.


As for redistribution, the router will have those routes under an IGP so if you are redistributing them you must refer to the IGP in question during the redistribution.




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milan.kulik Wed, 04/01/2009 - 16:03
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Hi Edison,


this is what I met in my lab:

I was redistributing from OSPF to BGP in a quite complicated configuration.

The router was running 12.2.

I noticed some prefixes were not advertised to a eBGP neighbor - those with r> in "sh ip bgp" output.


I might be missing something but it looks to me like inactive prefixes not advertised by BGP in 12.2.


I'll try to upgrade to 12.4 tomorrow (if I find an IOS fitting small Flash in my lab) and see what happens.


Rearding redistribution:

My understanding is a prefix must be the best one (i.e., present in RIB) to be redistributed. And this rule is hopefully still valid.


Thanks,

Milan




milan.kulik Thu, 04/02/2009 - 05:11
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Hi Edison,


I realized:

After IOS upgrade from 12.2(8)YJ to 12.3(11)YZ2 the inactive BGP prefixes started to be advertised.


On the contrary:

bgp suppress-inactive

has no effect, they are still advertised to the nieghbor.


Unfortunately, my lab router memory is too small to install 12.4.


So I believe I'm facing a bug in obsolete IOS versions here.


Thank you very much for your help!


BR,

Milan


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