RE: Simple Doubt regarding BGP

Nayyar,

The classful boundary with auto-summary enabled allows you to enter network 2.0.0.0 to pull in a /24 that falls within that class boundary. The same rule of having a matching existing route in your RIB applies here too:

Rack1R1(config-router)#auto-summary
Rack1R1(config-router)#net 2.2.2.2
Rack1R1(config-router)#do s deb
IP routing:
  BGP updates debugging is on for address family: IPv4 Unicast

Rack1R1(config-router)#net
*Apr 28 02:22:11.389: BGP: Import walker start version 0, end version 1
*Apr 28 02:22:11.389: BGP: ... start import cfg version = 0
Rack1R1(config-router)#net 3.3.3.3
Rack1R1(config-router)#do s ip b

Rack1R1(config-router)#net 2.0.0.0
Rack1R1(config-router)#
*Apr 28 02:22:59.701: BGP(0): route 2.0.0.0/8 up
*Apr 28 02:22:59.701: BGP(0): nettable_walker 2.0.0.0/8 route sourced locally
Rack1R1(config-router)#net 3.3.3.3 mask 255.255.255.255
Rack1R1(config-router)#
*Apr 28 02:23:30.009: BGP(0): route 3.3.3.3/8 up
*Apr 28 02:23:30.009: BGP(0): nettable_walker 3.0.0.0/8 route sourced locally
*Apr 28 02:23:30.009: BGP(0): nettable_walker 3.3.3.3/32 route sourced locally

And below is the added /24 in a class a boundary:

Rack1R1(config-router)#in lo 3
Rack1R1(config-if)#ip add
*Apr 28 02:26:33.789: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback3, changed state to up
Rack1R1(config-if)#ip add 4.4.4.4 255.255.255.0
Rack1R1(config-if)#exit
Rack1R1(config)#rb 100
Rack1R1(config-router)#net 4.0.0.0
Rack1R1(config-router)#
*Apr 28 02:26:55.761: BGP(0): route 4.0.0.0/8 up
*Apr 28 02:26:55.761: BGP(0): nettable_walker 4.0.0.0/8 route sourced locally

Rack1R1(config-router)#do s ip b
BGP table version is 5, local router ID is 150.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network Next Hop Metric LocPrf Weight Path
*> 2.0.0.0 0.0.0.0 0 32768 i
*> 3.0.0.0 0.0.0.0 0 32768 i
*> 3.3.3.3/32 0.0.0.0 0 32768 i
*> 4.0.0.0 0.0.0.0 0 32768 i

-ryan

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of nAyYAR
Sent: Monday, April 27, 2009 10:12 PM
To: Raghav Bhargava
Cc: ccielab_at_groupstudy.com
Subject: Re: Simple Doubt regarding BGP

Hi Raghav,

I believe the behavior is related to BGP auto-summary ... have a look at
this link it might help.

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a00800949e8.shtml#five

--------------------------------------------------
From: "Raghav Bhargava" <raghavbhargava12_at_gmail.com>
Sent: Tuesday, April 28, 2009 2:55 AM
To: "Cisco certification" <ccielab_at_groupstudy.com>
Subject: Simple Doubt regarding BGP

> Hi Experts,
>
> Very basic question
>
> Suppose I have this ip address configured on my loopback Interface of R1
>
> 2.2.2.2/8
>
> Now under my BGP Process if i advertise this network as
>
>
> network 2.2.2.2
>
> OR
>
> network 2.0.0.0
>
> Now in first case I don't see this network in the BGP table of the other
> router but
> if I follow the second case the network is seen.
>
> Can anyone please explain why is it doing like this??
>
> --
> Warm Regards
> Raghav
>
>
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Received on Mon Apr 27 2009 - 22:31:32 ART