for example
=========
if you see on router 1 sh ip bgp

   Network                 Next Hop            Metric LocPrf Weight Path
*>xxx.xxx.xxx.xxx     <lo router1>           0        100      0         AS1
AS33 AS6
*  xxx.xxx.xxx.xxx.    <lo router2>           0                    0
AS3 AS90 AS5

and on router 2

   Network                 Next Hop            Metric LocPrf Weight Path
*  xxx.xxx.xxx.xxx     <lo router1>           0        100      0
AS1 AS33 AS6
*>xxx.xxx.xxx.xxx.    <lo router2>           0                    0
AS3 AS90 AS5

with SAME number of as hops , it means that the route with '>' is the best
way to reach destination on each router, and for the same local-preference
(default 100 for all routes received). So your bgp work propely.

Now, for understanding, if you want destination to be reached through router
2 first, you have to tag the route received on router 2 from your ISP2 with
best local-preference (for example 150).

Then on sh ip bgp on both routers , you can see that the best route is
always through router 2.

router 1 and 2
=====
   Network                 Next Hop            Metric LocPrf Weight Path
*> xxx.xxx.xxx.xxx.    <lo router2>           0        150      0
AS3 AS90 AS5

The route via router disappear from the table, until the route via router 2
is not rachable.


Jacques VUVANT
Nerwork OPT New-Caledonia
Phone : +687-267541
Fax   : +687-278444
Mobile: +687-773121
Mail   : jacques.vuvant@...



I've had the same problem for understanding. Just think that is

----- Original Message -----
From: "Wim Godden" <housing@...>
To: <isp-bgp@isp-bgp.com>
Sent: Sunday, April 20, 2003 3:09 AM
Subject: [isp-bgp] iBGP not working properly ?


> Hi,
>
> We recently added a second transit link to our network and set up BGP on
the link.
>
> The current situation is this :
>
>
>                     PC
>                     |
> Switch1 -------- Switch2
>    |                |
> Router1 -------- Router2
>    |                |
> Transit1         Transit2
>
>
> Router1 has a BGP link to Transit1, Router2 to Transit2, both
> get the full routing table.
> Router1 and Router2 have an iBGP link.
>
> The 'loop' at Router1-Router2-Switch1-Switch2 uses STP, so no
> problems there. The default gateway for PC is Switch2, the
> default for Switch2 is Router2.
>
> So far, so good.
>
> When we connected Transit2 to Router2, we noticed that the
> routing table in both Router1 and Router2 changed quite a bit,
> which was to be expected. Most routes went via Transit2, which
> was normal, because the AS path length was shorter.
>
> However, when the path length is the same and we perform a
> traceroute on both Router1 and Router2 to the same host, they
> both go out via a different link... their own. I don't think
> that's normal, right ?
>
>
> Second problem : when I get a summary of the BGP, this is what
> I get :
>
> Router 1 :
> Core1# bgp show summary
> Neighbor        V    AS MsgRcvd MsgSent      Up/Down Prefixes
> Rcvd/Sent
> --------        -    -- ------- -------      ------- ---------
> ---------
> [Group Id: transit1]
> 212.23.45.137   4  8928   81494    9792   1d3h11m26s
> 120248/1
> [Group Id: ibgp]
> 62.213.192.18   4 28707  364891  169743   1d23h32m2s
> 115210/20896
> BGP summary, 2 groups, 2 peers
> Core1#
>
>
> Router 2:
> core2# bgp show summary
> Neighbor        V    AS MsgRcvd MsgSent      Up/Down Prefixes
> Rcvd/Sent
> --------        -    -- ------- -------      ------- ---------
> ---------
> [Group Id: transit2]
> 64.212.16.113   4  3549  235153    3328    1d3h42m9s
> 120464/1
> [Group Id: ibgp]
> 62.213.192.17   4 28707  128012  329835   1d23h34m7s
> 20898/115223
> BGP summary, 2 groups, 2 peers
> core2#
>
>
> If I read this correctly, Router1 only sent 20896 prefixes to
> Router2, although it received 120248 from Transit1. On the
> other hand, Router2 sent 115223 to Router1 and it received
> 120464 from Transit2... where does that difference come from ?
> Why doesn't Router1 send all of its routes to Router2 ? Is
> that the reason why most routes go via Transit2 ?
>
>
> Any suggestions would be very nice.
>
>
> Kind greetings,
>
> Wim
>
> ------------------------ANNOUNCEMENT---------------------------------
> ---------------------------------------------------------------------
>                          >> ISP Technology <<
> VPN, DNS Security Management, spam, 3G, WLAN Security, P2P, VoIP, PLC,
>                     802.11i, 802.1x and much more!
>        http://www.wispcon.com/spring2003/attend-sessionlist.asp
>         The 10th Annual ISPcon, Baltimore Waterfront Marriott
>                              April 23-25
> ----------------------------------------------------------------------
> ----------------------------------------------------------------------
>







------------------------ANNOUNCEMENT---------------------------------
---------------------------------------------------------------------
                         >> ISP Technology <<
VPN, DNS Security Management, spam, 3G, WLAN Security, P2P, VoIP, PLC,
                    802.11i, 802.1x and much more!
       http://www.wispcon.com/spring2003/attend-sessionlist.asp
        The 10th Annual ISPcon, Baltimore Waterfront Marriott
                             April 23-25
----------------------------------------------------------------------
----------------------------------------------------------------------

Replies

[isp-bgp] iBGP not working properly ?, Wim Godden