01-29-2012 09:38 PM - edited 03-04-2019 03:03 PM
Just need to know your expert opinion on this.
I have 2 provider independent prefixes advertised to our current 3 ISPs (ISP-A, ISP-B, ISP-C) via BGP. And I have another separate ISP (ISP-D) with its own IP prefix (ISP owned prefix) running default route only to ISP network (currently not member of BGP).
I plan to join ISP-D to existing BGP, advertising my 2 provider independent prefix plus the ISP owned prefix of ISP-D to this link. However I only want to advertise the ISP owned prefix to ISP-D and not to my other ISP. Meaning this prefix can only be reachable on the internet through ISP-D, inbound and outbound.
I am currently reading on Prefix List Policy Control and I just want to know if I am on the right track. Any ideas how it can be implemented? I will be testing this on lab.
E.g.
My AS: AS 100
Remote As: AS 200
Provider independent Prefixes:
10.10.10.0/23
10.10.11.0/23
ISP-D prefix (ISP owned):
193.10.10.0/23
Appreaciate your ideas.
Ciscoman
01-30-2012 12:29 AM
Im thinking of implementing NO-EXPORT community using prefix-list/route-map but I do not prefer applying filtering to every eBGP peer. In this case if i would go for the no-export community I will have to apply "send-community" and "route-map" to my existing peering with 3 ISPs.
Do you have any solutions for this?
01-31-2012 09:23 AM
Appreciate any comments.
Have you tried the "no-export" or "no-advertise" community in real world?
Thanks!
01-31-2012 11:28 AM
I am puzzled why you feel ok to configure all of the EBGP peers with a route map and a prefix list to set the community but do not want to configure the EBGP peer with a prefix list or a distribute list or a route map to prevent advertisement of the provider dependent prefix.
If you try to use the no export or no advertise community you will be advertising the provider dependent prefix to your immediate peers and it seems to me to be a problem if you advertise that prefix to any of the other external peers. So the best solution is some route filtering (distribute list, prefix list, or route map) on the EBGP peers.
HTH
Rick
01-31-2012 08:29 PM
Hi Rick,
Thanks for your response. I currently have outbound filter-list applied on all my eBGP peerings and I worried too much filtering might affect the performance of the router. Using community might be another alternative idea but considering your comments also with Rick below prefix-list or distribute-list will help.
If say I applied both filter-list and prefix-list on the neighbor statement do you see any issue?
Thanks.
- Richard
02-01-2012 05:37 AM
In the config all you need is to apply one.
Here is a link that has some basic info http://www.cisco.com/en/US/partner/tech/tk365/technologies_configuration_example09186a008009456d.shtml
Basically you would use one or the other but not both when performing the funciton of filtering.
router bgp 300
network 1.0.0.0
network 2.0.0.0
neighbor 10.10.10.10 remote-as 100
neighbor 10.10.10.10 route-map localonly out
neighbor 10.10.10.10 prefix-list ABC in
neighbor 20.20.20.20 remote-as 200
neighbor 20.20.20.20 route-map ROUTE-ADV out
neighbor 20.20.20.20 prefix-list ABC in
ip prefix-list ABC seq 5 permit 0.0.0.0/0
ip prefix-list localonly seq 5 10.10.10.0/24 le 32
ip prefix-list ROUTE-ADV seq 5 permit 10.0.0.0/24 le 32
ip prefix-list ROUTE-ADV seq 10 permit 10.1.0.0/24 le 32
route-map ROUTE-ADV permit 10
match ip address ROUTE-ADV
set ip local-preference 200
route-map localonly permit 10
match ip address localonly
This is a sample config taken off the cisco link provided but also a few additions so you can see the differences and how they are applied.
02-01-2012 12:00 PM
Richard
No I do not see any issues if you use both a prefix list and a filter list on a neighbor statement.
HTH
Rick
01-31-2012 10:55 AM
One of the quickest and most straight forward I can think of is creating prefix-list, call it ISP-D-ADV
Create route-map, call it ISP-D-ADV
apply route-map to neighbor statement out.
clear BGP session
verify your adv by doing sh ip bgp neigh
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