From: Cristian Henry H (chenry@reuna.cl)
Date: Tue Sep 30 2003 - 12:44:50 GMT-3
In mi opinion that behavior is absolutly normal.
First Router12 learn route 168.1.0.0 from Router76 with MED 33 and the
same route from AS350 with MED 42, so comparing MEDs it choose the route
from Router76 as valid one. Then Router12 send its "valids" routes to
Router76 so it should send back the route 168.1.0.0 learned from
Router76 (MED33), but by slip-horizon it doesn't send it.
If we start the same secuence but starting with Router76 learning the
route from both neighbors, it will choose the MED33 from AS350, so it
will send it to Router12 (not split horizon here). Then Router12 will
have both entries for the route.
Ken.Farrington@barclayscapital.com ha escrito:
>
> 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
> ----------------------------------------------------------------------------
> ---------------------------
>
> ________________________________________________________________
> Ken Farrington
> Global Networks, Barclays Capital, 5 The North Colonnade, Canary
> Wharf, London, E14 4BB
> * Tel : 020 7773 3550
> * Mob : 07768-866655
> * ken.farrington@barcap.com
>
> ------------------------------------------------------------------------
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> visit our web site at http://www.barcap.com.
>
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-- Cristian E. Henry REUNAE-mail: chenry@reuna.cl Fono: 56-2-3370336
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