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

[Patrick Okui]

Hi Alex,

Firstly .. you can not predict how many ASes someone is from you. So
getting prepends to work is going to be tough.

If you're willing to live with traffic to a particular /24 coming only
over a particular link then I'd suggest the following alternative:

On  30-May-2014 11:16:35 (+0300), Alex Rhys-hurn wrote:
> My prefixes are:
> 194.9.64.0/23
> 194.9.64.0/24
> 194.9.65.0/24
> 
> Announced as:
> 194.9.65.0/24 via Access Kenya with no prepend

I assume you want traffic to this /24 on access Kenya ... leave this as is.

> 194.9.64.0/24 via ISP1 prepended 3x

Remove this announcement on your link to Access Kenya (see below)

> 194.9.0.0/23 via Access Kenya with no prepend

Announce this prefix to Access Kenya so that if your link via Safaricom
goes down 194.9.64.0/24 is still reachable.

> 
> and
> 
> 194.9.64.0/24 via Safaricom with no prepend

Keep this (traffic to this /24 will only be on this link unless it goes
down)

> 194.9.65.0/24 via Safaricom prepended 3x

Remove this prefix from your advertisement to Safaricom

> 194.9.0.0/23 via Safaricom prepended 3x

Prepending on the /23 does nothing really. As long as a /24 route exists
for a particular route the /23 won't be used. If the /24s from Access
Kenya disappear, it's likely the /23 from there will to.

SO ... keep this announcement but _remove_ the prepends. This will only
be used if your link to Access Kenya goes down (to reach 194.9.65.0/24.)

Remember rule 1 of routing. The longest match wins.

--
patrick

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