From: Brian McGahan (brian@xxxxxxxxxxxxxxx)
Date: Sat Aug 10 2002 - 02:22:14 GMT-3
Kym,
BGP backdoor is actually the opposite of what you're saying
here. BGP backdoor is used when you have an IGP and an EBGP route to a
certain prefix, and you want to use the IGP route. EBGP learned routes
have an administrative distance of 20, which is lower than all IGP
learned routes. Therefore EBGP is preferred over an IGP route. BGP
backdoor modifies this behavior by tagging an EBGP learned route as a
backdoor route, and bumping the AD up to 200. See this link for more
detail:
http://www.cisco.com/warp/public/459/14.html#A14.0
As Howard mentioned, it is most likely a bad idea to change the
distance of your BGP learned routes, however there is always an
exception to every rule. You can change the distance of all BGP learned
routes with the command:
distance bgp [external-distance] [internal-distance] [local-distance]
You can also change the distance on a per route basis.
Distance [distance] [neighbor] [wildcard] [acl]
For example, if we want to change the distance of the prefix
1.2.3.0 learned from any neighbor to 30:
Access-list 1 permit host 1.2.3.0
!
router bgp 1
distance 30 0.0.0.0 255.255.255.255 1
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
http://www.cyscoexpert.com
Voice: 847.674.3392
Fax: 847.674.2625
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
kym blair
Sent: Friday, August 09, 2002 11:33 PM
To: chenyan@deeptht.com.cn; ccielab@groupstudy.com
Subject: Re: change the distance attribute of bgp
Chenyan,
I presume you are working on a scenario that requires you to change the
AD
from 200 to 20. Probably the routes learned between the IBGP peer
routers
are showing up in your routing table as OSPF or EIGRP routes because
they
have a better AD than IBGP (200), and your scenario wants you to learn
them
via BGP.
In that case, use the "neighbor X.X.X.X backdoor" statement. Using
"backdoor" on both routers will introduce some difficult problems (i.e.,
not
sharing routes with other BGP routers, so suddenly routes behind one or
both
of these routers are not reachable from other parts of the network).
This
is a very hard problem and is worth spending a lot of time practicing.
Good luck. Kym
>From: "chenyan" <chenyan@deeptht.com.cn>
>Reply-To: "chenyan" <chenyan@deeptht.com.cn>
>To: "ccielab" <ccielab@groupstudy.com>
>Subject: change the distance attribute of bgp
>Date: Sat, 10 Aug 2002 09:41:40 +0800
>
>hi,guys,
>
>I dont know is it poosible to change the distance attribute from
ibgp(200)
>to ebgp(20)?
>
>Thanks
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