Alcatel-Lucent 7750 SR-OS, Configuration Manual

Page: 82 / 674

Common Configuration Tasks
Page 82 7750 SR OS Router Configuration Guide
Creating an IP Address Range
An IP address range can be reserved for exclusive use for services by defining the
config>router>service-prefix
command. When the service is configured, the IP address
must be in the range specified as a service prefix. If no service prefix command is configured, then
no limitation exists.
The
no service-prefix ip-prefix/mask
command removes all address reservations. A
service prefix cannot be removed while one or more services use address(es) in the range to be
removed.
CLI Syntax:
config>router
service-prefix ip-prefix/mask [exclusive]
Configuring an LDP Shortcut
This command enables you to forward user IP packets and specified control IP packets using LDP
shortcuts over all network interfaces in the system that participate in the IS-IS and OSPF routing
protocols. The default is to disable the LDP shortcut across all interfaces in the system.
IGP Route Resolution
When LDP shortcut is enabled, LDP populates the RTM with next-hop entries corresponding to all
prefixes for which it activated an LDP FEC. For a given prefix, two route entries are populated in
RTM. One corresponds to the LDP shortcut next-hop and has an owner of LDP. The other one is
the regular IP next-hop. The LDP shortcut next-hop always has preference over the regular IP
next-hop for forwarding user packets and specified control packets over a given outgoing interface
to the route next-hop.
The prior activation of the FEC by LDP is done by performing an exact match with an IGP route
prefix in RTM. It can also be done by performing a longest prefix-match with an IGP route in
RTM if the aggregate-prefix-match option is enabled globally in LDP
ldp-interarea-prd .
Note that the LDP next-hop entry is not exported to LDP control plane or to any other control
plane protocols except OSPF, IS-IS, and specific OAM control plane as specified in
Handling of
Control Packets on page 84 .
This feature is not restricted to /32 FEC prefixes. However only /32 FEC prefixes will be populated
in the Tunnel Table for use as a tunnel by services.
All user and specified control packets for which the longest prefix match in RTM yields the FEC
prefix will be forwarded over the LDP LSP. The following is an example of the resolution process.