7206-VXR- Bgp configuration

Unanswered Question
May 10th, 2006
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Hi,


I am facing a problem on BGP, the thing is that i have advertise my prefix with network commond


bgp router XXXX


network 202.X.X.X


than i advertise same network (202.X.X.X) with my prfix list out bound and with some other prefix as well.


after apply the prefix list than i negaite the NO network 202.X.X.X , and then i reset bgp with clear command,


and chk my advertize prefix but the 202.X.x.x was not adertise. all other were adverised


soo i want to ask you what was the problem.


once agin chk my steps which i perfoprmed.


1) 202.X.X.X was alredy adverize

2) i advertise it again in outboud prefix list with some our customer prifix


3) i negate the 202.X.X.X as no network


but did no advertis ????? why


after that i agian adverise it with netwok commands.


Thanks



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cisand2002 Wed, 05/10/2006 - 03:56
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Hi,


When do a no network under bgp process. Do you still have route in routing table (sh ip ro 202.X.x.x)? is it in bgp table (sh ip bg 202.X.x.x )? do you have the right mask in the routing table and in the prfix list ?


Please send output from those commands.


HTH


cisand

afzaalq007 Wed, 05/10/2006 - 04:14
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Hi,


yes its present in routing table


#sh ip bgp 202.X.X.X

BGP routing table entry for 203.X.X.X/24, version 11751097

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Advertised to peer-groups:



each and every thing was ok,it is adverise by network command


but i want to ask you ,why it did not work when i applied Piefix list. while all there were advertise in same prefis list.


wht shuld be the standard procedure for adverising it via prefix list??????


Thanks

cisand2002 Wed, 05/10/2006 - 04:35
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is your prefix-list like this ?


ip prefix-list TRYIT permit 203.x.x.x/24


when you do a show ip prefix-list do you see any match for this entry ?

counters can be reset by entering the clear ip prefix-list command.


Can you also configure the mask in the network command?

router bgp 123

network 203.x.x.x mask 255.255.255.0


Please let me know the


cisand



afzaalq007 Wed, 05/10/2006 - 04:50
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hi


my prefix list is hust this


Seq 5 permit 202.X.X.X/24

seq 10 permit 202.X.X.X/24


and with the network command


network 202.X.X.X


it works well wit out the subnet mask


so wht is the standard procedure for advertizeing this with preix list.


thanks


cisand2002 Wed, 05/10/2006 - 05:08
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hello,


once you defined your prefix-list, you can use it like this


neighbor 1.1.1.1 prefix-list NAME out


can you also tell me where do you see the problem ?

I mean in the router or in the peer router ?


HTH,


P.S maybe you can post your router config.


Regards,


cisand

mheusinger Wed, 05/10/2006 - 05:16
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Hello,


first: a prefix-list does not advertise any network at all. It is solely used to filter updates of prefixes already present in the BGP table. So if a network is not present in the BGP table, the a prefix-list will not change this.


There are three possibilities to get a prefix into a routers BGP table.

1) learned through a BGP update from a BGP peer

2) inserted locally through "network X.X.X.X" - as you successfully did

3) inserted locally through redistribution of a network present in the IP routing table


So once you remove the network command, the BGP router is "instructed" not to insert the prefix locally. The prefix-list applied will have no impact on this behaviour.


Hope this helps! Please rate all posts.


Regards, Martin

afzaalq007 Wed, 05/10/2006 - 05:25
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Hi,


Very nice , thanks alot for answering in in detail,


now i have to advertise all my prefixes with network commands than they will be adverised ohter wise not okk ... am i right ????.


thanks once agian.









mheusinger Wed, 05/10/2006 - 05:34
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Hello,


You are right, this is one option to achieve the desired results!

You also can use redistribution f.e. mostly used in MPLS VPN environments. Or you take one network statement for each prefix. This is preferably used with ISPs for stability reasons.


Hope this helps! Please rate all posts.


Regards, Martin

afzaalq007 Wed, 05/10/2006 - 05:44
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Hi,


Thanks once agian.


i am rating ur answers but i dont know why it did not take is rate,


thanks agian.


afzaalq007 Wed, 05/10/2006 - 06:35
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Hi,


how can we use or implement the redistribution ??? plz forward any link ,,


for detail,


Thanks.


afzaalq007 Wed, 05/10/2006 - 06:35
User Badges:

Hi,


how can we use or implement the redistribution ??? plz forward any link ,,


for detail,


Thanks.


mheusinger Wed, 05/10/2006 - 06:52
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  • Green, 3000 points or more

Hello,


redistribution can be done through the command "redistribute", IF the routes are already in the IP routing table. Example:


router bgp 65000

redistrubute static


ip route 10.1.0.0 255.255.0.0 10.2.2.2


Example 2:


router bgp 65000

redistribute rip route-map RIP2BGP


router rip

version 2

network 10.0.0.0

no auto-summary


route-map RIP2BGP permit 10

match ip address prefix-list 123


ip prefix-list 123 seq 5 permit 10.1.0.0/16 le 24


A more detailed explanation can be found at:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_reference_chapter09186a00800ca759.html#wp1041381


or at "Connecting to a Service Provider Using External BGP"

http://www.cisco.com/en/US/products/ps6441/products_configuration_guide_chapter09186a008054e098.html


Hope this helps! Please rate all posts.


Regards, Martin


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