topic RE: BGP advertise-map in XOS in ExtremeSwitching (EXOS/Switch Engine)

BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 18:05:00 GMT

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

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 18:46:00 GMT

look towards configuring different localpref for different ISP-s

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 18:46:00 GMT

the reason why i am looking into the advertise-map becasue i want to affect inbound traffic , i used the community tags and as-prepend , it is not working as expected

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 18:46:00 GMT

do you use communities which your ISP-s understand?

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 18:46:00 GMT

Hi Nick , Yes i use the https://onestep.net to configure the communities . the thing is i have a backup link of just 10 mbps and if only one internet source tries to route inbound to me on this link it will get over utilized , so i am looking into a solution that works 100 percent .

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 18:46:00 GMT

But do your ISP-s support reading those communities?
You may find out that by
whois as65536 where 65536 is a number of autonomus system of your backup ISP

RE: BGP advertise-map in XOS

Balaji — Tue, 20 Jun 2017 19:24:00 GMT

Elie,

My understanding is that you would like to advertise only the public network to the ISP, with that in mind the below configuration should work. (please correct me if the requirement is something different)

Below is the policy to filter the routes to be advertised and the command to apply the policy for a neighbor.

edit policy Route_Filter

entry permit-route {
if match any {
nlri 10.249.2.0/24;
} then {
permit;
} }

configure bgp neighbor 10.250.1.12 route-policy out Route_Filter

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

They need to only advertise Public address if the primary link goes down .

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 19:24:00 GMT

Hi Balaji, thank you for your reply , your configuration is correct which accomplish half of what i am looking for , the other half is that i want to advertise only this public prefix only and only if the connection to the primary ISP Fails. ( i have 2 routers connected to 2 different ISPs)

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 19:24:00 GMT

my idea is to add a static blakchole route and track it by and ip sla , and add this route along with my public prefix in a route-map as an AND operation. so if the static route is there then permit the public prefix to be advertised

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

Elie, your idea is not correct
Your backup ISP should accept you announces with a minimal localpref
So your prefixes will be accepted only if your first BGP session fails

Our backup ISP does that automatically when we announce prefixes with a specific community:
whois as20850 | grep ackup remarks: | 20850:50 will set Local Preference to 50 for use as Backup

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 19:24:00 GMT

can you please explain more your idea or setup

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

which AS numbers of you uplink ISP-s?
I will help you to find out if your uplinks accept communities

RE: BGP advertise-map in XOS

Elie_Raad — Tue, 20 Jun 2017 19:24:00 GMT

Cognet AS 174 (Primary) Expedient AS 17054 Secondary

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

Well, both uplinks are in ARIN area -- they do not have a strict policy to have an up-to-date information about peering as in RIPE area:
Compare info about your secondary ISP https://whois.arin.net/rest/asn/AS17054 and our one: https://apps.db.ripe.net/search/lookup.html?source=ripe&key=AS20850&type=aut-num

Therefore, you should manually write an e-mail to Expedient support or NOC team to find out if they support communities or localprefs or if they cat accept your announces with a minimal local preference

RE: BGP advertise-map in XOS

Jarek — Tue, 20 Jun 2017 19:24:00 GMT

Hi Nick,

local preference is an attribute that routers exchange in the same AS.
eBGP peer is not aware about it.

--
Jarek

RE: BGP advertise-map in XOS

Jarek — Tue, 20 Jun 2017 19:24:00 GMT

Elie,

do you have your own AS and IP net block ?
Or you have some IP's from Cogent and some from Expedient ?

--
Jarek

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

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

RE: BGP advertise-map in XOS

Jarek — Tue, 20 Jun 2017 19:24:00 GMT

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

RE: BGP advertise-map in XOS

Nick_Yakimenko — Tue, 20 Jun 2017 19:24:00 GMT

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.