Configuring a Bypass Tunnel
Context
A bypass tunnel provides protection for a link or node on a primary tunnel. An explicit path and attributes must be specified for a bypass tunnel when manual TE FRR is being configured.
Bypass tunnels are established on selected links or nodes that are not on the protected primary tunnel. If a link or node on the protected primary tunnel is used for a bypass tunnel and fails, the bypass tunnel also fails to protect the primary tunnel.
Only the transit nodes on a TE tunnel support the fast reroute (FRR) function.
TE FRR does not take effect if multiple nodes or links fail simultaneously. After FRR switching is performed to switch data from the primary tunnel to a bypass tunnel, the bypass tunnel must remain Up when forwarding data. If the bypass tunnel goes Down, the protected traffic is interrupted and FRR fails. Even though the bypass tunnel goes Up again, traffic is unable to flow through the bypass tunnel but travels through the primary tunnel after the primary tunnel recovers or is reestablished.
By default, the system searches for an optimal manual FRR tunnel for each primary tunnel every 1 second and binds the bypass tunnel to the primary tunnel if there is an optimal bypass tunnel.
Perform the following configurations on the PLR.
Procedure
- Run system-view
The system view is displayed.
- Run interface tunnel tunnel-number
The view of the bypass tunnel interface is displayed.
- Run either of the following commands to assign an IP address to the tunnel interface:
To configure an IP address for the tunnel interface, run ip address ip-address { mask | mask-length } [ sub ]
The primary IP address must be configured before the secondary IP address is configured.
To configure the tunnel interface to borrow an IP address of another interface, run ip address unnumbered interface interface-type interface-number
An MPLS TE tunnel can be established even if the tunnel interface is assigned no IP address. The tunnel interface must obtain an IP address before forwarding traffic. An MPLS TE tunnel is unidirectional and does not need a peer address. Therefore, there is no need to configure a separate IP address for the tunnel interface. Generally, a loopback interface is created on the ingress node and a 32-bit address that is the same as the LSR ID is assigned to the loopback interface. Then the tunnel interface borrows the IP address of the loopback interface.
- Run tunnel-protocol mpls te
MPLS TE is configured as a tunneling protocol.
- Run destination dest-ip-address
A tunnel destination address is configured, which is usually the LSR ID of the egress.
Various types of tunnels require specific destination addresses. If a tunnel protocol is changed from another protocol to MPLS TE, a configured destination address is deleted automatically and a new destination address needs to be configured.
- Run mpls te tunnel-id tunnel-id
A tunnel ID is set.
- Run mpls te bypass-tunnel
A bypass tunnel is configured.
Routes and labels are automatically recorded after a bypass tunnel is configured.
A tunnel interface cannot be used for both a bypass tunnel and a backup tunnel. The mpls te bypass-tunnel command and the mpls te backup command cannot be configured simultaneously on the same tunnel interface.
A tunnel interface cannot be used for both a bypass tunnel and a primary tunnel. The mpls te bypass-tunnel and the mpls te fast-reroute command cannot be configured simultaneously on the same tunnel interface.
- Run mpls te protected-interface interface-type interface-number
The interface on which the bypass tunnel protects traffic is specified.
After a tunnel is specified to protect an interface, its corresponding LSP becomes the bypass LSP. You can establish a bypass LSP by configuring an explicit path on the PLR.
- The mpls te protected-interface command and the mpls te backup command cannot be configured simultaneously on the same tunnel interface.
- The mpls te protected-interface command and the mpls te fast-reroute command cannot be configured simultaneously on the same tunnel interface.
- (Optional) Run mpls te path explicit-path path-name [ secondary ]
An explicit path is configured for the bypass tunnel.
Before using this command, ensure that the explicit path has been created using the explicit-path command. Note that physical links of a bypass tunnel cannot overlap protected physical links of the primary tunnel.
- (Optional) Run mpls te bandwidth ct0 bandwidth
Set the bandwidth for the bypass tunnel.
- Run commit
The configurations are committed.