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IMPLEMENTING A TOPOLOGY TRANSPARENT ZONE IN OPEN SHORTEST PATH FIRST (OSPF)

IP.com Disclosure Number: IPCOM000236130D
Publication Date: 2014-Apr-07
Document File: 4 page(s) / 47K

Publishing Venue

The IP.com Prior Art Database

Related People

Alvaro Retana: AUTHOR [+2]

Abstract

An approach is presented to enable topology transparent zone in an Open Shortest Path First (OSPF) network. A virtual overlay routing instance is created for routing information distribution, while an underlying instance is maintained for data forwarding.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 48% of the total text.

Page 01 of 4

IMPLEMENTING A TOPOLOGY TRANSPARENT ZONE IN OPEN SHORTEST PATH FIRST (OSPF)

AUTHORS:

Alvaro Retana Yi Yang

CISCO SYSTEMS, INC.

ABSTRACT

    An approach is presented to enable topology transparent zone in an Open Shortest Path First (OSPF) network. A virtual overlay routing instance is created for routing information distribution, while an underlying instance is maintained for data forwarding.

DETAILED DESCRIPTION

    The number of routers in an Open Shortest Path First (OSPF) area or domain increases as the Internet traffic keeps growing, which presents scalability challenges to OSPF as it requires a larger Link State Database (LSDB) and routing table. OSPF is a link-state routing protocol for Internet Protocol (IP) networks.

    In the IETF, it has been recently proposed to deploy topology-transparent zones (TTZs) in OSPF. A topology-transparent zone (TTZ) comprises a group of routers and a number of links connecting these routers.

    There are three types of routers in a network with TTZs: TTZ external routers, TTZ internal routers, and TTZ edge routers. A TTZ external router is a router whose interfaces are all out of the TTZ. A TTZ internal router is a router whose interfaces are all inside the TTZ. A TTZ edge router is a router that has some interfaces inside TTZ (internal interfaces), and some interfaces out of TTZ (external interfaces).

    A TTZ external router is not aware of the zone. The information about the internal links and internal routers is not distributed to external routers. Any link state change inside the zone, such as a link up or down, is not visible to these external routers either.

    Presented herein are techniques to enable TTZ gracefully, and which minimize backward compatibility issues. No change is introduced on TTZ internal routers or external routers.

Copyright 2014 Cisco Systems, Inc.
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Page 02 of 4

Edge Router Discovery and Adjacency Establishment

    Each TTZ edge router originates a router information link state advertisement (LSA), indicating its edge router identity, and floods it through the area as specified in RFC 4970. Edge routers use this router information LSA to detect each other.

    After a TTZ edge router detects a remote edge router, it builds a tunnel adjacency with the remote edge router.

LSA Origination

    Each TTZ edge router originates an (inner) router LSA, advertising its internal and external interfaces, but not tunnel interfaces, and floods this inner router LSA over its internal interfaces. This inner router LSA may also include stub links attached on the edge router. In effect, this inner router LSA is the LSA that would be formed had the tunnel adjacencies not been established.

    Each TTZ edge router also originates an (outer) router LSA, advertising its external interfaces and the tunnel interfaces, but not internal interfaces, and floods this outer router LSA over its external interfaces and tunnel interfaces. This outer router LSA may also include stub links (representing a summary) for the prefixes...