RE: auto-summary (BGP)

From: Moffat, Ed (EMoffat@fsci.com)
Date: Sun Mar 28 2004 - 01:55:11 GMT-3


The last sentence is confusing. I don't think it applies to redistributed
routes - at least not in the 12.2(19) that I am running. Here is what I have
found.

If I redistribute routes from my IGP with auto-summary disabled the subnets
will show up in my EBGP peers table.

If I redistribute and enable auto-summary I will receive the classful route
only in the BGP table.

If I do not redistribute but orginate with a classful network command with
auto summary enabled, I will insert a classful route in the BGP table and
advertise it to EBGP neighbors.

If I do not redistribute but orginate with a classful network command with
auto-summary disabled, no routes will be added to the BGP table or announced
unless there is a classful address in the RT (via IGP summary address,
static to Null0, etc.).

If I orginate with a classful network command with auto-summary disabled and
there is a classful match in the RT then that classful route will be
advertised.

-Ed-

-----Original Message-----
From: David Hurtado [mailto:dei2viccie@hotmail.com]
Sent: Saturday, March 27, 2004 5:54 PM
To: ccielab@groupstudy.com
Subject: auto-summary (BGP)

Hello everybody,

I've been reviewing "auto-summary (BGP)" command and the Doc CD explains
something that i cannot understand:

"By default, BGP does not accept subnets redistributed from Interior Gateway
Protocol (IGP). To advertise and carry subnet routes in BGP, use an explicit
network command or the no auto-summary command. If you disable automatic
summarization and have not entered a network command, you will not advertise
network routes for networks with subnet routes unless they contain a summary
route."

I don't understand what the last sentence is trying to explain. Please, if
somebody could give me some example or a link that explains it in a better
way i would be very grateful.

Thanks for the help



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