nanog mailing list archives

Re: distinguishing eBGP from show ip BGP


From: Reza Motamedi <motamedi () cs uoregon edu>
Date: Wed, 11 Mar 2015 15:42:06 -0400

What I ultimately want to determine, is the location of the AS connection.
I know for example the router is in, say LA. If hot potato lets me to send
the packet to the neighbor AS then they have an AS connection in LA, right?

Going back to my example does the fact that the entry does not have 'i'
mean that I can send it to AS2828 on the next hop.

    Network          Next Hop            Metric LocPrf Weight Path
 *  207.108.0.0/15   216.156.2.164            3             0 2828 209 i
 *                   65.106.7.101             2             0 2828 209 i
 *                   65.106.7.246             3             0 2828 209 i
 *                   65.106.7.55              3             0 2828 209 i
 *>                  216.156.2.162            2             0 2828 209 i

Best Regards
Reza Motamedi (R.M)
Graduate Research Fellow
Oregon Network Research Group
Computer and Information Science
University of Oregon

On Wed, Mar 11, 2015 at 3:30 PM, Mark Tinka <mark.tinka () seacom mu> wrote:



On 11/Mar/15 21:22, Reza Motamedi wrote:

Thanks Mark for the reply. Let me try to check what I understood is
correct. Does the 'i' on the left (status code) only shows whether the
prefix belongs to this AS?


Status-code "i" just means the entry was learned by "this" router via
iBGP. It does not mean the entry belongs to "this AS".

A locally-generated route can be thought of as "belonging to this AS",
however, a router cannot assert that a locally-generated route "belongs to
this AS". It just asserts that the route was locally-generated within the
AS. Ownership of the route is data that needs to be gleaned from other
sources, e.g., RIR WHOIS data, speaking to the operator, e.t.c.

Whatever the case, a locally-generated route would not have an AS_PATH.
That is an easy way to tell for such a use-case.

 What I want to figure out is if this two ASes (the owner of the router
and and the first one on the AS-PATH) connect at the location of the
router, or if packets need to stay for some hops in the local AS.


So you want to determine whether traffic is hot- or cold-potato forwarding
from the point of view of your reference router?

Mark.



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