BGP advertise-map in XOS

[Elie_Raad]

I have a Multi-homed Routers connected to 2 ISPs. I need to Create like an Advertise-map on the Standby Router connected to the Standby ISP to only advertise my Public address if the primary link goes down .

Is there a way of doing it in XOS ?
Thank You,
Elie

[Nick_Yakimenko]

Yes, e.g. if you announce your prefixes to as20850 with community 20850:50 -- they will accept your announce and change localpref to 50
Please see https://apps.db.ripe.net/search/lookup.html?source=ripe&key=AS20850&type=aut-num

[Jarek]

You mean: upstream can accept BGP community that will change localpref for your prefix  ?

--
Jarek

[Nick_Yakimenko]

Jarek, that's the point I'm trying to explain
Or your upstream can manually accept your prefixes with a different localpref if you ask them to do that.

[Jarek]

Nick,

please see RFC4277 (https://tools.ietf.org/html/rfc4277)

Page 6 says:

BGP has a separate metric parameter for IBGP and EBGP. This allows policy-based metrics to overwrite the distance-based metrics; this allows each autonomous system to define its independent policies in Intra-AS, as well as Inter-AS. BGP Multi Exit Discriminator (MED) is used as a metric by EBGP peers (i.e., inter- domain), while Local Preference (LOCAL_PREF) is used by IBGP peers (i.e., intra-domain) ... and so on...

As a customer you can't add localpref direct in your ISP/Upstream/Transit AS.
Your ISP/Upstream/Transit can configure for customers on their own router/routers BGP community that you could use to change localpref for your prefix/prefixes in their AS.

--
Jarek

[Nick_Yakimenko]

I do not agree with you:
If an ISP gets all prefix announces from their uplinks with, say, localpref 100, and from a specific customer on a direct link they get prefix announces with 50, then direct announce will become active only if their prefix will become invisible from their uplinks