What is the source IP address of the device you're using to do the
traceroutes?
What is the destination IP address of the device you're using to do the
traceroutes?
If neither of them are AT route-views, you can't expect the path to
match exactly what is seen at route-views. Of course the next hop
router has BGP of its own.
Thatte, Sachin wrote:
Pete,
Looks like you misunderstood my question, I do understand PHB of IP
routing and TTL expired response from a router could be from different.
My questions simply was is the next hop router route-views has BGP of
his own?
thx for ur response
sachin
-----Original Message-----
From: Pete Templin [mailto:petelists@...]
Sent: Tuesday, June 22, 2004 5:07 PM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] Re: BGP path inconsistent with traceroute
Thatte, Sachin wrote:
Can somebody shed light on the following issue?
From route-views I see as-path best path for network
198.207.185.0/24 from as 3549 but the traceroute uses 701. Could it
be because route-views uses ebgp-multihop and the actual IP
next-hop router has bgp table of his own which is different than
that of route-views?
Each BGP router has its own table. This means several things:
1) If at least one endpoint of your traceroute isn't located at
route-views, you might travel over a route completely different than
what route-views shows.
2) Routers perform destination-based forwarding. At each hop
along the
way, the responding router forwards its response out its best
path back
to the source, so you're seeing the IP address of the
interface that the
packet is coming back from, not necessarily the IP address the packet
was forwarded to (but you are seeing the router the packet
was forwarded
to).
3) Likewise, each of those routers along the way has a unique
view back
to the source of the traceroute. A traceroute that started
from within
198.207.185.0/24 and headed to the point where you've been conducting
your traceroutes might follow a completely different path than what
you're seeing.
pt
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