[c-nsp] Inbound redundancy with two ISPs

Sascha E. Pollok nsp-list at pollok.net
Thu Nov 1 12:20:28 EDT 2007


Steve,

> So, if I understand you right, this is what you would propose, assuming
> that you were provider 'A', and it was your /24 you were assigning to
> the OP:
>
> - 'A' routes a /24 to OP
> - OP advertises the /24 to provider A and B via BGP with personal local
> preferences in place
> - A advertises it's aggregate including the /24 to the 'net
> - B advertises the more specific /24 prefix to the 'net
> - OP uses an ASN from the private range, which both A & B must agree to
> honour
>
> I'd really like to understand this, because I've never had to deal with
> a situation where I've received a prefix from one ISP and needed to
> multi-home with it. (I have my own ARIN prefix).
>
> Will the more specific /24 route advertised to the 'net by B not be the
> preferred route at all times?

"A" would normally advertise the aggregate + the /24 as long as he still
wants to put some traffic on the invoice sent to OP ;-) Good for routing
table growth *sigh

Sascha

--
Sascha E. Pollok, CCNP               E-Mail: sp at iphh.net
Manager Network Operations           Tel: +49 (0)40 374919-10
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