From: James (james@towardex.com)
Date: Wed Sep 15 2004 - 20:34:08 GMT-3
On Thu, Sep 16, 2004 at 12:01:00AM +0200, Joseph Rothstein wrote:
> Hi Guys,
>
> I know what the problem is, but I am not sure how I get the results that I do compared to the author's.
>
> As far as BGP path selection goes, I believe that the path selection comes down to number, 10, and does not go to 12.
>
> "10. Prefer the route that can be reached through the closest IGP neighbor...." Although I am not sure if this applies to external routes as wella sinternal.
eBGP routes are preferred over iBGP routes before the IGP cost issue.
BGP by default has what we call "hot potato" behaviour, where a default configuration
will always seek out closest exit point to leave the local AS. So when you have iBGP,
nexthop with smallest igp cost is preferred. Likewise, when you have iBGP and eBGP,
eBGP is preferred.
>
> In this case, since the IGP section asks you to manipulate the bandwidth of the links between R1-R4 and R6-R4, 256 ans 512 respectively, the preferred path is to 10.6.6.6 like the bgp table shows since it has the lower OSPF metric.
What is the active igp path on R6 to get to 10.90.90.x? Does it go over the
Ethernet instead?
Do a 'sh ip route 10.90.90.1' on R4, R6, R1 so we can see the cost of that route.
Also doing 'sh ip bgp 2.2.2.0' on all 3 routers would give us more information such
as the metric derived from RIB for the next hop.
HTH,
-J
-- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
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