AS announcement question (easy)

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1

Hi, sorry for this low-level question, but at least I'm not posting in html.
:slight_smile:

My company owns a class C, and we're switching ISPs. The "new" provider is
telling us that they can start announcing, without us having to tell the old
provider to stop announcing. I.e., a 2-3 day period where both are
announcing our class C.

This conflicts with my extremely (admittedly)limited knowledge. Can someone
let me know if this is OK/not OK?

Thanks in advance,

Mike

Michael Donahue
WATG
(949) 574-8500 x261

2

Originating the same prefix from two different ASes violates the RFC (or
whatever bible you might pray to), but works most of the time.

See "show ip bgp inconsistant-as" on cisco. YMMV.

3

Hi, NANOGers.

] See "show ip bgp inconsistant-as" on cisco. YMMV.

On that theme, please also see:

   <http://www.cymru.com/BGP/incon01.html>
   <http://www.cymru.com/BGP/incon01-list.html>

Thanks,
Rob.

4

Hi, sorry for this low-level question, but at least I'm not posting in html.
:slight_smile:

My company owns a class C, and we're switching ISPs. The "new" provider is
telling us that they can start announcing, without us having to tell the old
provider to stop announcing. I.e., a 2-3 day period where both are
announcing our class C.

This conflicts with my extremely (admittedly)limited knowledge. Can someone
let me know if this is OK/not OK?

If you are going to have your link up to both providers during that time, it
would not be a problem. However, if your /24 is nailed into the tables of
your previous provider, and your link to that provider is down, then the old
provider will create a blackhole for /24 for anyone who prefers the path
presented by your old provider.

In general, one really *should* coordinate switching between providers if
ones' announcement is originated by the provider.

Alex

5

Inconsistant origins are bad. Which path is supposed to be believed?
Which path is supposed to be selected? From what point of view? None
of these are defined conditions; non-determinism is not good for
performance. Expect some things to work, some things to be strange,
and some to be lousy.

Your best bet is to minimize the overlap period.

Joe