same site of Origin value on PE

[cisc0.ameer]

hello to all

suppose we have multiple PE , then each two of them use soo but same value

for example

we have PE 1 and PE 2 : PE1 ->CE1  & PE2->CE 2

strange thing which i've not seen before in both PE used same soo values for example

PE1)neighbor 1.2.3.4 soo 100:1

PE2)neighbor 4.3.2.1 soo 100:1

soo has been used to avoiding Loop and not install same Prefix into CE

but i think it has to uses different soo value in order to reach this aim

but why in a scenario i saw configuration was like this ; same soo in PE router

and it has repeated for remaining PE !!!!!

can you please give any scenarios condition(s) which this solution applicable ?i mean using same soo

thanks and regard

[Giuseppe Larosa]

Hello cisc0.amer,

if you use the same Site of origin extcommunity means that PE1 and PE2 connect to the SAME VRF customer site that is multihomed we could call it a site with two PE nodes and two CE nodes. (2PE2CE)

It is a correct configuration and it is the reason why SOO has been introduced.

Hope to help

Giuseppe

[cisc0.ameer]

thanks for your answer

you mean something like below picture diagram ?

Ok , NOW i get it ....so it's not compulsory PE uses different soo values in case if both using same VRF

so we can take both PE represent onr router if they use same VRF ...

thanks

[Giuseppe Larosa · Accepted solution]

Hello cisc0.ameer,

yes your network diagram represents a multihomed VRF site with two PE nodes connected to two different CE nodes serving the same site.

In this case it is more appropriate to use the same SOO on both PE nodes in order to avoid unwanted re-injection of routes for example to CE1of routes coming from CE2 via PE2 and then PE1.

When PE1 sees the same SOO extcommunity on the VPNv4 route it knows that it doesn't need to send to CE1 a route with the same SOO even if CE1 is not advertising that prefix anymore.

Of course a PE-CE routing protocol should be in use to make the use case for SOO.

OSPF has its own mechanism the down bit to avoid learning an LSA generated by another PE node.

For EIGRP or BGP SOO can add a protection mechanism.

Hope to help

Giuseppe