MPLS and RSVP-TE
86
MPLS Guide
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3.10 RSVP-TE 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”.
Unnumbered IP interfaces can be used via RSVP-TE for signaling traffic engineering
(TE) LSPs.
Supporting RSVP-TE over unnumbered interfaces requires the ability to:
• carry TE information over unnumbered links in IS-IS-TE or OSPF-TE extensions
• specify unnumbered interfaces in RSVP-TE signaling
An unnumbered IP interface is identified uniquely on a router in the network by the
tuple (router ID, ifindex). An LSR at each end of the link assigns a system-wide
unique interface index to the unnumbered interface. IS-IS, OSPF, MPLS (RSVP-TE,
LDP), and OAM use this tuple to advertise the link information, signal LSPs over the
interface, or send and respond to an MPLS echo request message over an
unnumbered interface.
The borrowed IP address for an unnumbered interface is configured using the
following CLI command, with the default value set to the system interface address:
config>router>interface>unnumbered {ip-int-name | ip-address}.
To support unnumbered TE links in IS-IS, a new sub-TLV of the extended IS
reachability TLV is added, which encodes the link local identifiers and link remote
identifiers as defined in RFC 5307, IS-IS Extensions in Support of Generalized Multi-
Protocol Label Switching (GMPLS).
To support unnumbered TE links in OSPF, a new sub-TLV of the Link TLV is added,
which encodes the link local identifiers and link remote identifiers as defined in RFC
4203, OSPF Extensions in Support of Generalized Multi-Protocol Label Switching
(GMPLS).
Note: The borrowed IP address is used exclusively as the source address for IP packets
that originate from the interface. For FRR, this address must be configured to an address
different from the system interface in order for the FRR bypass LSP to come up at the
ingress LER. See RSVP-TE Fast Reroute (FRR) for information on FRR.
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