Enabling the Labeled IPv4 Route Exchange

In inter-AS VPN Option C, a BGP LSP needs to be established between ASs, and labeled IPv4 routes need to be exchanged between BGP peers.

Procedure

Configuring the PE
1. Access the system view.
```
system-view
```
2. Access the BGP view.
```
bgp { as-number-plain | as-number-dot }
```
3. Enable the exchange of the labeled IPv4 routes with the ASBR in the same AS.
```
peer ipv4-address label-route-capability
```
Configuring the ASBR
1. Access the system view.
```
system-view
```
2. Access the view of the interface connected to the peer ASBR.
```
interface interface-type interface-number
```
3. Set the interface IP address.
```
ip address ip-address { mask | mask-length }
```
4. Enable the MPLS function.
```
mpls
```
5. Return to the system view.
```
quit
```
6. Access the BGP view.
```
bgp { as-number-plain | as-number-dot }
```
7. Enable the exchange of the labeled IPv4 routes with the PE of the same AS.
```
peer ipv4-address label-route-capability
```
  In the Option C solution, establish an inter-AS VPN LSP. The related PEs and ASBRs exchange public network routes with the MPLS labels.
  
  The ASBR establishes a common EBGP peer relationship with the remote ASBR to switch labeled IPv4 routes.
  
  The public network routes with the MPLS labels are advertised by the MP-BGP. Based on RFC 3107 (Carrying Label Information in BGP-4), the label mapping information of a route is carried by advertising BGP updates. This feature is implemented through BGP extension attributes, which requires BGP peers to process the labeled IPv4 routes.
  
  By default, BGP peers cannot process labeled IPv4 routes.
8. Specify the peer ASBR as the EBGP peer.
```
peer ipv4-address as-number { as-number-plain | as-number-dot }
```
9. (Optional) Configure the maximum number of hops for the EBGP connection.
```
peer { ipv4-address | group-name } ebgp-max-hop [ hop-count ]
```
  Generally, one or multiple directly connected physical links exist between EBGP peers. If the directly connected physical link(s) are not available, run the peer ebgp-max-hop command to ensure that the TCP connection can be set up between the EBGP peers through multiple hops.
10. Enable the exchange of the labeled IPv4 routes with the peer ASBR.
```
peer ipv4-address label-route-capability [ check-tunnel-reachable ]
```
  - If tunnel reachability checking is enabled, BGP advertises IPv4 unicast routes to peers when routed tunnels are unreachable or advertises labeled routes to peers when routed tunnels are reachable. This eliminates the risk of establishing an MP-EBGP peer relationship between PEs over a faulty LSP because this will cause data forwarding failures.
  - If tunnel reachability checking is disabled, BGP advertises labeled routes to peers whether the tunnels for imported routes are reachable or not.