LDP Signaling and Services

When LDP is enabled, targeted sessions can be established to create remote adjacencies with nodes that are not directly connected. When service distribution paths (SDPs) are configured, extended discovery mechanisms enable LDP to send periodic targeted hello messages to the SDP far-end point. The exchange of LDP hellos trigger session establishment. The SDP signaling default enables tldp. The service SDP uses the targeted-session parameters configured in the config>router>ldp>targeted-session context.

The SDP LDP and LSP commands are mutually exclusive; either one LSP can be specified or LDP can be enabled. If LDP is already enabled on an MPLS SDP, then an LSP cannot be specified on the SDP. If an LSP is specified on an MPLS SDP, then LDP cannot be enabled on the SDP.

To enable LDP on the SDP when an LSP is already specified, the LSP must be removed from the configuration using the no lsp lsp-name command. For more information about configuring SDPs, see the 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Overview Guide.

The following example displays the command syntax usage to configure enable LDP on an MPLS SDP:

config>service>sdp#
    — ldp
    — signaling {off | tldp}

The following displays an example of an SDP configuration showing the signaling default tldp enabled.

A:ALA-1>config>service>sdp# info detail
----------------------------------------------
            description "MPLS: to-99"
            far-end 10.10.10.99
            signaling tldp
            path-mtu 4462
            keep-alive
                hello-time 10
                hold-down-time 10
                max-drop-count 3
                timeout 5
                no message-length
                no shutdown
            exit
            no shutdown
----------------------------------------------
A:ALA-1>config>service>sdp# 

The following displays an example of an SDP configuration for the 7750 SR, showing the signaling default tldp enabled.

A:ALA-1>config>service>sdp# info detail
----------------------------------------------
            description "MPLS: to-99"
            far-end 10.10.10.99
            ldp
            signaling tldp
            path-mtu 4462
            keep-alive
                hello-time 10
                hold-down-time 10
                max-drop-count 3
                timeout 5
                no message-length
                no shutdown
            exit
            no shutdown
----------------------------------------------
A:ALA-1>config>service>sdp# 

The following shows a working configuration of LDP over RSVP-TE (1) where tunnels look like the second example (2):

Example 1 — LDP over RSVP-TE

*A:ALA-1>config>router>ldp# info
----------------------------------------------
            prefer-tunnel-in-tunnel
            interface-parameters
                interface "port-1/1/3"
                exit
                interface "port-lag-1"
                exit
            exit
            targeted-session
                peer 10.51.0.1
                    shutdown
                    tunneling
                        lsp "to_P_1"
                    exit
                exit
                peer 10.51.0.17
                    shutdown
                    tunneling
                        lsp "to_P_6"
                    exit
                exit
            exit
----------------------------------------------
*A:ALA-1>config>router>ldp#

Example 2 — Tunnels

ALA-1>config>router>if-attr# info
----------------------------------------------
            
admin-group "lower" value 2 
admin-group "upper" value 1 
----------------------------------------------
*A:ALA-1>config>router>mpls# info
----------------------------------------------
            resignal-timer 30
            interface "system"
            exit
            interface "port-1/1/3"
            exit
            interface "port-lag-1"
            exit
            path "dyn"
                no shutdown
            exit
            lsp "to_P_1"
                to 10.51.0.1
                cspf
                fast-reroute facility
                exit
                primary "dyn"
                exit
                no shutdown
            exit
            lsp "to_P_6"
                to 10.51.0.17
                cspf
                fast-reroute facility
                exit
                primary "dyn"
                exit
                no shutdown
            exit
            no shutdown
----------------------------------------------
*A:ALA-1>config>router>mpls#