Discussion

All routes that are part of the VPN are identified by a route distinguisher, which you
define with the set route-distinguisher command:
[edit routing-instances VPN2]
aviva@RouterG# set route-distinguisher 65500:02
You can specify the route distinguisher in two ways. This recipe uses the AS number
followed by a colon and an identifying value. You can also use an IP address followed
by a colon and an identifying value. Neither format is better than the other.
The format you choose depends entirely on your design and specific requirements.
Using the IP address:value format allows you to identify the originating PE router
when you are looking at a route and its communities, because you normally set the
IP portion to the PE router’s lo0 address. This format can assist with troubleshooting
and operational monitoring. Using the AS:value format has the advantage of leaving
more space for the Administrator variable (four bytes instead of two bytes).
Service providers often choose this second format, using the value field to hold a
numeric customer identifier. When looking at routes, this format makes it possible,
on a network-wide basis, to identify the customer associated with a route.
For the VPN to know which routes belong to it, you define a VRF target using the
set vrf-target command:
[edit routing-instances VPN2]
aviva@RouterG# set vrf-target target:65520:100
The command sets the route target (the target VPN), which is one of the BGP
extended community attributes. The VRF target identifies which route belongs to
which VPN and allows the VPN to accept routes into its VRF routing table and to
advertise them.
The set vrf-target command also associates a default import and export policy with
the VRF routing table to accept and advertise routes. The default policy uses the configured
target, here 65520:100, as the match condition for routes received from
remote PE routers. As the import policy states, any routes containing this target are
placed into the VRF table. Similarly, when sending routes to local PE routers, the
export policy is for the VPN to advertise any routes matching this target. The default
routing policy is a simple policy that would look something like this if you configured
it manually:
[edit policy-options]
aviva@RouterG# set community VPN2 members target:65500:2
[edit policy-options policy-statement VPN2-import-policy]
aviva@RouterG# set term 1 from protocol bgp
aviva@RouterG# set term 1 from community VPN2
aviva@RouterG# set term 1 then accept
aviva@RouterG# set term 2 then reject
[edit policy-options policy-statement VPN2-export-policy]
aviva@RouterG# set term 1 from protocol static
Setting Up a Simple Layer 3 VPN | 561
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