Multi-Homed Routing

Tom tom at
Tue Sep 2 10:11:59 PDT 2003

On Tue, 2 Sep 2003, Haesu wrote:

> >
> >   Plus, some have suggested just advertising your existing assignments
> > from your other provider.  Bad idea.  Most providers address allocated
> > is not portable.  Check WHOIS for "ADDRESSES WITHIN THIS BLOCK ARE
> > NON-PORTABLE".  Besides, even if your existing provider's IP blocks work,
> > and your provider allows you to do this (you should always ask first),
> > you'll be advertising a more specific prefix of one of their larger
> > blocks.  Guess what that will do?
> Obviously you have not had enough experience working with BGP customers.
> Longer matches always win. Your provider announces the aggregate.

  Where did I say differently?  "more specific" means a longer match.

> It's funny to say I've had up to /20 being announced elsewhere with
> provider's permission even when whois shows ADDRESSES WITHIN THIS BLOCK
> ARE NON-PORTABLE. Most providers will not care as long as you can
> justify why you want to announce the block elsewhere, and as long as you
> properly register them at IRR.
> Yes IRR routing registry is only as good as the networks that use it.
> But you know what? Major carriers do use them, and those who filter
> routes on RIR registration boundaries either a) point a default route to
> elsewhere or b) build filter based on IRR.

  Yes, most carriers do use them.  But a major carrier is not going to use
some fly-by-night route registry.  In fact, several carriers operate their
own registries, and don't trust information from anywhere else.

> Try peering with some big national carrier-- they will not peer with you
> if you do not use IRR -- especially in US.

  Doing that already.

> Frankly, if you are a backbone filtering /24s, you obviously don't know where
> to get to the internet if you are not even using IRR. Even our good old
> friends at Verio is accepting our announced /24's now as long as registered in
> the IRR.

  And you sure they are getting farther than that?  I see only three /24s
from your AS (presumably 27552), and a /21 and a /22.

> >   But you need to know what you doing.  If you dump the routing table,
> > you'll see that many networks can't even do basic route summaries.
> You mean aggregation? I don't follow.

  At least 10% of the routes in the table are unnecessary.

> -hc
> --
> Sincerely,
>   Haesu C.
>   TowardEX Technologies, Inc.
>   WWW:
>   E-mail: haesu at
>   Cell: (978) 394-2867


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