What can I infer from "show ip route" and similar BGP commands?

Mon Dec 8 23:48:21 UTC 2014

Hello NANOG,

I’m a researcher and I was trying to understand the data I collected from
some BGP Looking Glasses. Basically, I was hoping to see if BGP records can
tell me where my university’s provider (AS3701) is peering with its
providers. I issued two BGP queries to Level3’s LGs, one in Seattle and one
in Amsterdam for my school’s prefix. My strong guess was that our provider
(AS3701) peers with Level3 in Seattle. I was hoping to conclude something
like this: if the peering occurs in Seattle, the Seattle LG should reveal
it, but Amsterdam should not.

AS3701 is Nero (Network for Education and Research in Oregon) which I
assume is a small regional AS. I don't think Nero peers with Level3 in
Amsterdam, however, I get this AS for my next hop even when I issue the
command from Amsterdam. On the other hand “car1.Sacramento1” suggests that
the peering happens in Sacramento.

This result makes me think what I get is from a combination of iBGP and
eBGP, which is also apparent from “Internal/External” keywords in the data.
My main issue is that the keywords are not always available. In some other
LG I just get a next hop IP and an AS path. How can I make sure that the
peering information comes from an eBGP peering? I think the next hop IP
might be the answer, right?

I included the results of the command for both LGs here, hopefully somebody
could explain to me

-------------------------------------------------

Route results for 128.223.0.0/16 from Amsterdam, Netherlands

BGP routing table entry for 128.223.0.0/16

Paths: (2 available, best #1)

 3701 3582

 AS-path translation: { OREGONUNIV UONET }

car1.Sacramento1 (metric 58341)

  Origin IGP, metric 0, localpref 100, valid, internal, best

  Community: North_America  Lclprf_100 Level3_Customer United_States
Sacramento

  Originator: car1.Sacramento1

 3701 3582

 AS-path translation: { OREGONUNIV UONET }

car1.Sacramento1 (metric 58341)

  Origin IGP, metric 0, localpref 100, valid, internal

  Community: North_America  Lclprf_100 Level3_Customer United_States
Sacramento

     Originator: car1.Sacramento1

-------------------------------------------------

Route results for 128.223.6.81/16 from Seattle, WA

BGP routing table entry for 128.223.0.0/16

Paths: (4 available, best #3)

 3701 3582

 AS-path translation: { OREGONUNIV UONET }

4.53.150.46 from 4.53.150.46 (ptck-core1-gw.nero.net)

  Origin IGP, localpref 90, valid, external

  Community: North_America  Lclprf_90 Level3_Customer United_States Seattle
Level3:11847

 3701 3582, (received-only)

 AS-path translation: { OREGONUNIV UONET }

4.53.150.46 from 4.53.150.46 (ptck-core1-gw.nero.net)

  Origin IGP, localpref 100, valid, external

  Community: Level3:90

 3701 3582

 AS-path translation: { OREGONUNIV UONET }

car1.Sacramento1 (metric 34363)

  Origin IGP, metric 0, localpref 100, valid, internal, best

  Community: North_America  Lclprf_100 Level3_Customer United_States
Sacramento

  Originator: car1.Sacramento1

 3701 3582

 AS-path translation: { OREGONUNIV UONET }

car1.Sacramento1 (metric 34363)

  Origin IGP, metric 0, localpref 100, valid, internal

  Community: North_America  Lclprf_100 Level3_Customer United_States
Sacramento

  Originator: car1.Sacramento1

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