Ldp Support For Unnumbered Interfaces - Nokia 7705 SAR-W Series Manual

MPLS Guide
Graceful handling of resources implements a capability by which the LDP interface
to the peer, or the targeted peer in the case of a targeted LDP (T-LDP) session, is
shut down.
If LDP tries to resolve a FEC over a link or a T-LDP session and runs out of data path
or CSM resources, LDP brings down that interface or targeted peer, which brings
down the Hello adjacency over that interface to all linked LDP peers or to the targeted
peer. The interface is brought down for the LDP context only and is still available to
other applications such as IP forwarding and RSVP LSP forwarding.
After taking action to free up resources, the user must manually perform a no
shutdown command on the interface or the targeted peer to bring it back into
operation. This re-establishes the Hello adjacency and resumes the resolution of
FECs over the interface or to the targeted peer.

5.1.12 LDP Support for Unnumbered Interfaces

Unnumbered interfaces are point-to-point interfaces that are not explicitly configured
with a dedicated IP address and subnet; instead, they borrow (or link to) an IP
address from another interface on the system (the system IP address, another
loopback interface, or any other numbered interface) and use it as the source IP
address for packets originating from the interface. For more information on support
for unnumbered interfaces, refer to the 7705 SAR Router Configuration Guide,
"Unnumbered Interfaces".
This feature allows LDP to establish a Hello adjacency and to resolve unicast FECs
over unnumbered LDP interfaces.
For example, LSR A and LSR B are the two endpoints of an unnumbered link. These
interfaces are identified on each system with their unique link local identifier. The
combination router ID and link local identifier uniquely identifies the interface in IS-IS
throughout the network.
A borrowed IP address is also assigned to the interface to be used as the source
address of IP packets that must originate from the interface. The borrowed IP
address defaults to the system interface address, A and B in this example. The
borrowed IP interface can be configured to any IP interface by using the following CLI
command: config> router>interface>unnumbered {ip-int-name | ip-address}.
The fec-originate command, which defines how to originate a FEC for egress and
non-egress LSRs, includes a parameter to specify the name of the interface that the
label for the originated FEC is swapped to. For an unnumbered interface, this
parameter is mandatory because an unnumbered interface does not have its own IP
address.
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