From: Craig Dorry (chdorry@yahoo.com)
Date: Tue Sep 30 2003 - 09:51:00 GMT-3
Yes, this is normal - see the link listed below.
Based on normal BGP path selection you prefer lowest
MED (which is the metric value you mention being sent
to you) before you choose an eBGP over iBGP route.
http://www.cisco.com/en/US/tech/tk365/tk80/technologies_tech_note09186a0080094431.shtml
--- Ken.Farrington@barclayscapital.com wrote:
> Hello all,
> I have a question re the setup below.
>
> I have two routers peering eBGP with an external AS
> 350 and iBGP between the
> routers which (just for info) are separate
> locations.
>
>
> Now if I receive a route (say 168.1.0.0) that has a
> metric inbound on both
> routers (router76 route for this network has metric
> of 33 ,and Router12 has
> metric for this route of 42) it looks as if the
> router that has the lowest
> metric from the route, does not accept the iBGP
> route from the other router
> with the higher metric, but the router with the
> higher metric accepts the
> iBGP route from the router with the lower metric.
>
>
> If I receive a route where the metric is not set and
> all attributes are the
> same, it send each other the iBGP route (like
> 168.41.0.0) and uses it's
> local exit point via eBGP to that network.
>
> Please can someone confirm that this is normal
> operation for iBGP.
>
> Many thx indeed,
> Ken
>
>
>
>
> \ 168.1.0.0 168.224.0.0 168.41.0.0 /
> \ External /
> \ AS 350 /
> \__________________________________/
> |192.168.42.253 |192.168.41.254
> | |
> |eBGP |eBGP
> | |
> | |
> | AS 300 |
> +--------+ +--------+
> |Router76|---------------------|Router12|
> +--------+ iBGP +--------+
> 192.168.42.253 192.168.41.253
>
>
> on Router76
>
> router bgp 300
> neighbor 150.5.36.129 remote-as 300
> neighbor 192.168.42.254 remote-as 350
>
>
> Router76>sh ip int brief
> Interface IP-Address OK? Method
> Status
> Protocol
> Ethernet0 unassigned YES unset
> administratively down down
> Ethernet1 192.168.42.253 YES NVRAM up
> up
> Loopback0 150.5.32.65 YES NVRAM up
> up
>
> Network Next Hop Metric LocPrf
> Weight Path
>
----------------------------------------------------------------------------
> ---------------------------
> *> 168.1.0.0 192.168.42.254 33
> 0 350 i This
> entry only appears once
>
----------------------------------------------------------------------------
> ---------------------------
> *>i168.224.0.0 192.168.41.254 31 100
> 0 350 i
> * 192.168.42.254 42
> 0 350 i
>
----------------------------------------------------------------------------
> ---------------------------
> * i168.41.0.0 192.168.41.254 100
> 0 350 i This
> entry appears on both
> *> 192.168.42.254
> 0 350 i This
> entry appears on both
>
----------------------------------------------------------------------------
> ---------------------------
>
>
>
>
>
> On Router12
>
> !
> router bgp 300
> neighbor 150.5.32.65 remote-as 300
> neighbor 192.254.41.254 remote-as 350
> !
>
> Router12>sh ip int brief
> Interface IP-Address OK? Method
> Status
> Protocol
> Ethernet0 unassigned YES unset
> administratively down down
> Ethernet1 192.168.41.253 YES NVRAM up
> up
> Loopback0 150.5.36.129 YES NVRAM up
> up
>
> Network Next Hop Metric LocPrf
> Weight Path
> * 168.1.0.0 192.168.41.254 42
> 0 350 i
> *>i 192.168.42.254 33 100
> 0 350 i
>
----------------------------------------------------------------------------
> ---------------------------
> *> 168.224.0.0 192.168.41.254 31
> 0 350 i This
> entry only appears once
>
----------------------------------------------------------------------------
> ---------------------------
> *> 168.41.0.0 192.168.41.254
> 0 350 i This
> entry appears on both
> * i 192.168.42.254 100
> 0 350 i This
> entry appears on both
>
----------------------------------------------------------------------------
> ---------------------------
>
>
>
>
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