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.

The benefits of using unnumbered interfaces are the following:

• ISP backhaul can be enabled with a single IP address allocated to the CE nodes (the network interface address is coupled with the system IP address).

• Nodes can be added to or deleted from a network without address changes; unnumbered interfaces are linked to a centralized IP address and therefore do not require any address change if the nodes are relocated. After a topology change, the ARP table is updated to ensure reachability, and the upper layer protocols re-establish the peering sessions.

Unnumbered interfaces are supported on:

• network interfaces

• IES interfaces

• VPRN interfaces

Only IPv4 addresses are supported.

On the 7210 SAS-K 2F6C4T and 7210 SAS-K 3SFP+ 8C, unnumbered interfaces are supported for the IS-IS and OSPF routing protocols and for MPLS routing (RSVP-TE and LDP). This feature is supported through both dynamic and static ARP. Any Ethernet port with null, dot1q, or QinQ encapsulation supports IP unnumbered interfaces.

See the 7210 SAS-K 2F6C4T, K 3SFP+ 8C Routing Protocols Guide for more information about IS-IS and OSPF unnumbered interface support. See ‟Unnumbered Point-to-Point Interface in RSVP” and ‟Unnumbered Interface Support in LDP” in the 7210 SAS-K 2F6C4T, K 3SFP+ 8C MPLS Guide for more information about MPLS unnumbered interface support.