Auto Export

Auto export is a route leaking enhancement that’s design to operate locally on a PE router between different VRFs that require the sharing of routing information. When using traditional procedures leaking routes between remote PEs is carried out using custom VRF import and export policies to extend the scope of VPNv4 prefixes that are announced via MP-BGP and received within a different target VRF on a remote PE.

Due to the BGP split horizon rule it’s not possible to carry out route leaking locally on a PE as split horizon dictates that a BGP speaker cannot advertise routes back to itself; this is an inherent protection feature in BGP to avoid routing loops.

The auto-export feature is used as a simplistic method of overcoming this locally on the PE; auto export can be configured on each of the VRFs that require leaked routes to allow routes to be shared across VRFs that have matching route target communities. The route target communities are either gleaned from the vrf-target configuration within the VRF or from the policy tied to vrf-import/export statements within the VRF.

Due to the BGP split horizon rule and the fact that auto export is local feature, any routes that are shared between VRFs are not announced from the secondary target VRF that receives the leaked routes; the routes will only be announced via MP-BGP from the VRF that originated them.

To configure auto export is very straight forward. Two VRFs are shown below, in this case both VRFs are using a standard vrf-target community statement which matches and therefore allows routes to be leaked. In other cases different VRFs will have different route-targets so custom import and export policies will need to be configured to allow the routes to be leaked by expanding the scope of the VRF import policies between the respective VRFs.

routing-instances {
vpn-a {
instance-type vrf;
interface ge-0/0/0;
vrf-target target:65001:100;
routing-options {
auto-export;
}
protocols {
bgp {
group ce-1 {
peer-as 65002;
as-override;
neighbor 10.10.10.10;
}
}
}
}
}

routing-instances {
vpn-b {
instance-type vrf;
interface ge-0/0/1;
vrf-target target:65001:100;
routing-options {
auto-export;
}
protocols {
bgp {
group ce-1 {
peer-as 65002;
as-override;
neighbor 10.10.11.10;
}
}
}
}
}

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