The mixed-LSP mode of operation allows for a maximum of two LSP types to be configured within an SDP; a primary LSP type and a backup LSP type. An RSVP primary LSP type can be backed up by an LDP LSP type.
An LDP LSP can be configured as a primary LSP type, which can then be backed up by a BGP LSP type.
At any specific time, the service manager programs only one type of LSP in the line card, which activates it to forward service packets according to the following priority order:
RSVP LSP type
One RSVP LSP can be configured per SDP. This is the highest priority LSP type.
LDP LSP type
One LDP FEC is used per SDP. The 7210 SAS does not support LDP ECMP.
BGP LSP type
One RFC 3107-labeled BGP prefix programmed by the service manager.
In the case of the RSVP/LDP SDP, the service manager programs the NHLFEs for the active LSP type, preferring the RSVP LSP type over the LDP LSP type. If no RSVP LSP is configured or all configured RSVP LSPs go down, the service manager reprograms the line-card with the LDP LSP, if available. If not, the SDP goes operationally down.
When a higher priority LSP type becomes available, the service manager reverts back to this LSP at the expiry of the revert-time timer or the failure of the currently active LSP, whichever comes first. The service manager then reprograms the line card accordingly. If the infinite value is configured, then the SDP reverts to the highest priority LSP type only if the currently active LSP failed.
LDP uses a tunnel down damp timer which is set to three seconds by default. When the LDP LSP fails, the SDP will revert to the RSVP LSP type after the expiry of this timer. For an immediate switchover this timer must be set to zero. Use the configure>router>ldp>tunnel-down-damp-time command. For more information, see the 7210 SAS-Mxp, R6, R12, S, Sx, T MPLS Guide.
If the value of the revert-time timer is changed, it takes effect only at the next use of the timer. Any timer which is outstanding at the time of the change is restarted with the new value.
In the case of the LDP/BGP SDP, the service manager prefers the LDP LSP type over the BGP LSP type. The service manager reprograms the line card with the BGP LSP, if available; otherwise, it brings down the SDP operationally.
The following are differences in behavior of the LDP/BGP SDP compared to that of an RSVP/LDP SDP:
For a specific /32 prefix, only a single route exists in the routing table: the IGP route or the BGP route. Therefore, either the LDP FEC or the BGP label route is active at any specific time. The impact of this is that the tunnel table needs to be reprogrammed each time a route is deactivated and the other is activated.
The SDP revert-time cannot be used, because there is no situation where both LSP types are active for the same /32 prefix.