[afnog] Help Please - is my ISP Stripping my prepends?

[Mark Tinka]

On Friday, May 30, 2014 10:16:35 AM Alex Rhys-Hurn wrote:

> Announced as:

From what I can see (using our [SEACOM's] looking 
glass located in Mombasa, Kenya - you're welcome 
to use it too if you wish - http://lg.seacomnet.com/):

> 194.9.65.0/24 via Access Kenya with no prepend

Router: lg-01-mba.ke
Command: show ip bgp 194.9.65.0/24


BGP routing table entry for 194.9.65.0/24, version 8691796
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Refresh Epoch 1
  37100 3741 15808 37166
    41.87.100.25 from 41.87.100.25 (41.217.212.5)
      Origin IGP, metric 0, localpref 100, valid, external, best
      Community: 37100:10362 37100:10901 37100:10902 37100:12009
      path 0D880D68 RPKI State not found
      rx pathid: 0, tx pathid: 0x0

So yes, looks like there are no prepends here, as you
say.

> 194.9.64.0/24 via ISP1 prepended 3x

Router: lg-01-mba.ke
Command: show ip bgp 194.9.64.0/24


BGP routing table entry for 194.9.64.0/24, version 7506326
Paths: (1 available, best #1, table default)
  Not advertised to any peer
  Refresh Epoch 1
  37100 33771 37061 37061 37061 37061 37061 37166
    41.87.100.25 from 41.87.100.25 (41.217.212.5)
      Origin IGP, metric 0, localpref 100, valid, external, best
      Community: 37100:10000 37100:10900 37100:12002 37100:20901
      path 12149280 RPKI State not found
      rx pathid: 0, tx pathid: 0x0

This path looks like it's being prepended 4x times by
AS37061 (which looks like One Communications - not sure
whether this is a Safaricom subsidiary or customer).

> 194.9.0.0/23 via Access Kenya with no prepend

Router: lg-01-mba.ke
Command: show ip bgp 194.9.0.0/23


% Network not in table

Was this a typo?

> yes, as per your email, I am not seeing the expected
> behaviour from ISP 2 Safaricom. But now that I look
> again, I see paths to safaricom that are prepended
> (their AS 37061) being prepended 5x so my path is still
> shorter via my prepended path on Access Kenya. Should I
> just ramp up my prepending on Access Kenya?

I guess the real question is if you are prepending your own
AS to that path, why is your provider overwriting it?

The net effect is about the same, given the path is being
prepended by your provider anyway, but perhaps you want
to chat to them about whether you prefer they honour your
own prepends.

Cheers,

Mark.
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