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

Hamish McGlinn hmcglinn at gmail.com
Tue Dec 9 04:12:04 UTC 2014


Hi there,

Perhaps this would be easier and help you out:

http://bgp.he.net/AS3701#_graph4


Cheers,

Hamish

On Tue, Dec 9, 2014 at 12:48 PM, Reza Motamedi <motamedi at cs.uoregon.edu>
wrote:

> 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
>



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