Mailing List Archive: [nsp] set as-path tag

Hi,

Anyone out there have any experience with Cisco "set as-path tag"?
Cisco on-line documentation sez:

Converts the tag of a route into an autonomous system path. Applies
only when redistributing routes into BGP.

My brief lab tests show it working as I had desired with the following:

- a static pull-up route with tag of the ASN the route is to
originate in, and
- a BGP network statement with route-map that includes "set as-path tag"

I am checking with Cisco contacts as well, but while I wait for that
response let me check with you folks, too. I'm curious how long
that feature has been around, what caused Cisco to put this in (rather
than just making "set as-path prepend XXX" do the job in BGP network
statements as well as inbound/outbound neighbor route-maps), whether
there's any way to specify an as-path longer than a single ASN, bugs,
gotchas, etc.

Thanks. I'll gladly summarize to the list.

Jay B.

--
Jay Borkenhagen jayb@braeburn.org

On Tue, 3 Sep 2002 15:52:03 -0400 Jay Borkenhagen <jayb@braeburn.org> wrote:
> Anyone out there have any experience with Cisco "set as-path tag"?
[snip]
> I am checking with Cisco contacts as well, but while I wait for that
> response let me check with you folks, too. I'm curious how long
> that feature has been around, what caused Cisco to put this in (rather
> than just making "set as-path prepend XXX" do the job in BGP network
> statements as well as inbound/outbound neighbor route-maps), whether
> there's any way to specify an as-path longer than a single ASN, bugs,
> gotchas, etc.

It's been in IOS since the early days of IOS BGP, 11.2 certainly but
possiblyearlier. CCO suggests it's been around since 11. 0 but that may
just be the set as-path prepend form of the command. It's certainly nothing
new - it's mentioned in Doyle Vol.II and IIRC also Halabi.

I've no idea if it is of anything more than historical interest these days.
Certainly no one I know would redistribute BGP into an IGP and back on the
'net but someone might be using it on a private BGP network. The original
use of the command was so that you could do BGP-IGP-BGP redistribution and
not have to run BGP on all your devices.

Having said that I should be careful making statements about what people
will and won't do with BGP - it's quite flexible and there are a lot of
unusual uses of it about!

--
Ryan O'Connell
Mail: ryan@complicity.co.uk
CV: http://www.complicity.co.uk/ryancv.pdf
CCIE #8174