Iteration of L3VPN Services to an SR Tunnel
Iteration of Basic VPN Services to an SR Tunnel
If an Internet user uses a carrier network that performs IP forwarding to access the Internet, core carrier devices on the forwarding path need to learn a large number of Internet routes. This imposes a heavy load on core carrier devices and affects the performance of these devices. To solve this problem, you can configure VPN services iterated to an SR tunnel so that users can access the Internet through the tunnel.
- Deploy IS-IS on both ends of PEs to implement reachable routes.
- Set up a BGP peer relationship between the PEs to learn VPN routes from each other.
- Establish an IS-IS SR tunnel between PEs to allocate public network labels and compute the label forwarding path.
- Allocate a private network label to the VPN through BGP, for example, Label Z.
- Iterate the VPN routes to the SR tunnel.
- After PE1 receives an IP packet, encapsulate the private network label and the public network labels, and forward the packet based on the label forwarding path.
VPN FRR
As shown in Figure 5-29, PE1 adds the optimal route advertised by PE3 and the secondary optimal route advertised by PE4 to a forwarding entry. The optimal route is used for traffic forwarding, and the secondary optimal route is used as a backup route.
Failure Point |
Protection Switchover |
|---|---|
P1-to-P3 link |
Since BFD for SR-MPLS BE is not supported, PE1 cannot detect that the tunnel goes Down and VPN FRR cannot be performed to switch traffic to PE4, as shown in LSP3 in blue. If IS-IS FRR is configured, FRR is performed on P1. After the switchover is performed, traffic passes through PE1 -> P1 -> P2 -> P4 -> P3 -> PE3, as shown in LSP2 in red. If IS-IS FRR is configured, the SR-MPLS BE tunnel on the P node is used for hard convergence. The converged traffic passes through PE1 -> P1 -> P2 -> P4 -> P3 -> PE3, as shown in LSP2 in red. |
PE3 |
If PE3 is faulty, FRR switchover cannot be performed on LSP1 and traffic cannot be switched. PE1 detects PE3 failure through IS-IS packets. After re-convergence, LSP1 goes Down, and traffic is switched to LSP3 through PE1 -> CE1 -> PE2 -> P2 -> P4 -> PE4, as shown in LSP3 in red. |