From: Bell, Mark (Houston) (m.bell@xxxxxxxxxx)
Date: Mon Oct 02 2000 - 23:53:11 GMT-3
I have attempted to configure a conditional advertisement in my network
using the following config:
router bgp 3
no synchronization
neighbor 10.10.1.3 remote-as 2
neighbor 10.10.1.3 advertise-map BACKUP non-exist-map BACKUP2
neighbor 10.10.1.5 remote-as 3
neighbor 10.10.1.5 route-reflector-client
neighbor 10.20.1.2 remote-as 3
neighbor 10.20.1.2 route-reflector-client
!
ip classless
no ip http server
ip as-path access-list 1 permit _\(65005\)$
!
access-list 1 permit 6.0.0.0
access-list 2 permit 11.1.0.0
route-map BACKUP permit 10
match ip address 1
!
route-map ASPATH permit 10
match as-path 1
set local-preference 500
!
route-map BACKUP2 permit 10
match ip address 2
When I go to the router 10.10.1.5 that advertises 11.1.0.0/16 and shut down
it's link to this router, 11.1.0.0/16 disappears from the BGP table as
expected. If I understand conditional advertisements correctly, the router
should begin advertising 6.0.0.0/8 to 10.10.1.3 because 11.1.0.0/16 is gone.
The problem is, 6.0.0.0/8 never shows up anywhere.
Does the backup route have to be present in the BGP table prior to the
monitored route disappearing or will it be injected into the BGP table only
when necessary? Are there any restrictions as to whether the monitored or
backup route must be learned via iBGP or eBGP?
-----Original Message-----
From: Stylen [mailto:globalfx@netropolis.net]
Sent: Friday, September 29, 2000 21:26
To: ccielab@groupstudy.com
Subject: Re: Conditional BGP Advertisements
Yes, BGP will look for the route in its routing table, if it goes away, then
the routes in the advertise list will be advertised via eBGP. this is used
for backing up a link, i.e. if you have two routers connected to to a
external network. You might only want one of them advertising a specific
route, perhaps because of location, but if the link between that router and
the external network goes down, then the second router will begin
advertising the route for redundancy. if you have the second router watch
for the link between the first router and the external network in its
routing table, when the route goes dissappears, then it knows to advertise
the route designated by advertise-map.
Internet
| |
| |204.0.0.4/30
R1------R2
|
|
204.2.3.0/24
the 204.0.0.5 route will be in R1's routing table, via a IGP. when the link
between R2 and the internet goes down, then the 204.0.0.5 route will
dissappear from the routing table in R1 then R1 will advertise the route to
204.2.3.0/24 to the internet. When the 204.0.0.4/30 route comes back up, R1
will stop advertising 204.2.3.0/24, and R2 will take over.
Richard Foltz, CCNP, CCNP-Voice, CCDP, MCSE+I, Network+, A+
Technical Solutions Consultant
Sprint ENS
-----Original Message-----
From: abdul_rahim@ccsi.canon.com <abdul_rahim@ccsi.canon.com>
To: ccielab@groupstudy.com <ccielab@groupstudy.com>
Date: Friday, September 29, 2000 7:58 PM
Subject: Conditional BGP Advertisements
>The following statement as described on cisco in BGP routing process
>neighbor a.b.c.d advertise-map <route-map 1> no-exist-map <route-map 2>
>
>
>Advertises the routes specified in route-map1 when it finds that the routes
>specified in route-map 2 does not exists any more in the BGP table
>And they call it as Conditional Advertisement
>
>My question is that the routes in route-map1 ,do they have to be present in
>the BGP table,
>I am not getting the point at all
>
>Can some body explain it to all of the group in a bit detail or redirect to
>a certain URL ,I do have the URL on cisco sit
>http://cisco.com/warp/public/459/34.html
>
>Any feedbacks would be highly appreciated
>Thanks
>Abdul
>
>
>
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