From: Cristian Henry H (chenry@reuna.cl)
Date: Mon May 12 2003 - 12:14:49 GMT-3
Try using no-export community
OhioHondo ha escrito:
>
> Note:
>
> When you redistribute from BGP to OSPF, look at the LSA Type 5 entries of
> the BGP routes redistributed into OSPF. They are already "tagged" with the
> AS number from where they came.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Yadav, Arvind K (EM, GECIS)
> Sent: Monday, May 12, 2003 3:46 AM
> To: 'Robert Yee'; ccielab@groupstudy.com
> Subject: RE: how can I prevent my AS from becoming a transit AS? (kinda
> lo ng)
>
> 1. When you redistribute BGP router learned from AS300 on R2 and R1 to OSPF
> mark some tag (By using route-map) to all routes and while redistributing
> back to BGP on R1 and R2
> filter the tag routes with tag. In that way you can prevent your AS to
> becoming a transit AS.
> 2. ip as-path access-list 1 permit ^$ pm both the router R1 and r2
>
> Arivnd
>
> -----Original Message-----
> From: Robert Yee [mailto:robert@bluespud.com]
> Sent: Monday, May 12, 2003 10:27 AM
> To: ccielab@groupstudy.com
> Subject: how can I prevent my AS from becoming a transit AS? (kinda
> long)
>
> Given the following scenario, how can I prevent my AS from becoming a
> transit AS:
>
> ----- -----
> |AS100| |AS300|
> ----- -----
> \ /
> \ /
> ---------------------------
> | \ / |
> | R1----iBGP---R2 |
> | \ / |
> | \ / |
> | OSPF OSPF |
> | \ / |
> | \ / |
> | R3 |
> |AS200 (OSPF) |
> ---------------------------
>
> AS 300 advertises 10.1.1.0 /24 to AS 200 through R2.
>
> The 2 edge routers in AS 200 are running BGP and OSPF. R3 is running OSPF
> and has numerous routes that it is advertising to R1 and R2.
> Syncronization in BGP is disabled, so there
> should be no issue with bgp/ospf sync.
>
> The 2 edge routers are running mutual redistribution between the IGP and
> EGP.
>
> R2 redistributes 10.1.1.0 /24 from BGP into OSPF. Eventually, this route
> will reach R1 from OSPF (and from iBGP) and will be redistributed back into
> BGP from OSPF. Since OSPF has
> a better AD than iBGP, the OSPF route will be placed into routing table,
> and BGP will pick the redisributed route as the best path. This route will
> then get advertised to AS 100.
>
> Because OSPF is redistributing many routes to BGP, I think the best solution
> would be to put the following filter-list (skip ditribute-list,
> prefix-list, route-map) on each edge
> router:
>
> ip as-path access-list 1 permit ^$
>
> This filter list should only allow routes out that have no AS-PATH attribute
> associated with it.
>
> This should prevent AS 200 from being a transit area (if we were only
> running BGP), BUT since we are mutually redistributing, 10.1.1.0 /24 now is
> seen by BGP on R1 as route w/out
> an AS-PATH attribute.
>
> Then 10.1.1.0 /24 gets advertised out to AS 100.
>
> Is there any way around this?
>
> This situation would also apply to routes received from As100
-- Cristian E. Henry REUNAE-mail: chenry@reuna.cl Fono: 56-2-3370336
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