JNCIS-SP: VPLS.

A little look into configuring a basic multihomed MPLS VPLS (the BGP signaled one) on Junos. The scenario on which I am configuring is the following;



scenario


The routers in the grey area form an MPLS network. There are two route-reflectors serving the PE’s on which the configuration is done.

The VPLS is configured on the customer facing PE’s only, in this case R24, R19 and R17. On R24, we will configure a site with a single connection. On R19 and R17, we will configure the multihomed site. Only the connection with the highest preference will be up. The other connection is used only when the primary is down.

The three routers on top are the customer routers. They have one IP address configured on the interface that faces the PE. Since their configuration is so incredibly standard, I will stick the PE’s in this case.
Let’s look at the configuration on R24. This site is the site with a single connection in our VPLS:



scenario


The three routers on top are the customer routers. They have one IP address configured on the interface that faces the PE. Since their configuration is so incredibly standard, I will stick the PE’s in this case.
Let’s look at the configuration on R24. This site is the site with a single connection in our VPLS:



scenario


Let’s look at the configuration on R24. This site is the site with a single connection in our VPLS:
This is the standard MP-BGP signaled VPLS part. The interface with the VPLS configuration, the route-distinguisher, the route-target, etc.
Let’s move on to the multihomed part and have a look at the configuration of the secondary connection on R19:



scenario


The only difference here is the SITE part. Here, we can see two additional configuration statements configured under the ‘SITE-1’ stanza;
    • multi-homing
    • site-preference

The first configuration statement, the multihoming statement, specifies to the PE router that this site is part of a multihomed site. The PE router will, when no BGP-peers are available, deactivate the interfaces for the site.
The second configuration statement, the site-preference, is the local-preference that will be set on the advertisement of the label-block . We can see this on the route-reflector. The local-preference corresponds to the configured site-preference;



scenario


Now, onto the primary connection of this site. Under the routing-instance stanza, R17 will only have one statement that differs from the configuration on R19. This differing statement is setting the site preference to 300.
The complete routing-instance configuration in the case of R17 is as follows:



scenario


Let’s move over to one of the route-reflectors. For the entire bgp.l2vpn.0 table, we can now see only 2 routes. One route is towards the single site configured on R24. The other route is a route towards the primary connection of the multihomed site. This was the connection with a site preference of 300 configured on R17;



scenario


On R24, we can see that the router only learned about the primary location. The secondary location has not been signaled towards R24;



scenario


This means that when the primary goes down, the secondary location has to have its label block advertised via the route-reflector before R24 will be able to use it.
You can speed this up by altering the route-distinguisher on R19. When you alter the route-distinguisher to a unique value, you’ll make sure that the route will be known on R24.
Let’s do this on R17;



scenario


And check back on R24 again;



scenario


Here you can see that additional state information is available on R24. This will save (some) time when the communication to the primary site is lost.

11-9-2014