OSPF Overhaul Boosts IP Performance

FRAMINGHAM (07/21/2000) - Since 1990, the Open Shortest Path First protocol has enabled routers to govern the IP networks. The OSPF protocol applies to routing, which allows everything else on a network to work.

Recently, OSPF underwent a complete overhaul. OSPF Version 3 now permits routers to forward IPv6 data across networks, according to the Internet Engineering Task Force (IETF).

OSPF Version 3 boosts versatility so networks can be adapted to changing requirements. It allows complex networks to be simplified and includes enhancements to ensure that upgrades integrate safely and easily. OSPFv3 also has been streamlined, and its security has been increased.

A main goal of OSPFv3 was to "create a routing protocol independent of any specific network layer," says co-designer John Moy. To accomplish this, OSPFv3's inter-router messages have been redesigned. Unlike past versions, OSPFv3 doesn't insert IP-based data in the headers that begin its packets and link state advertisements (LSA). To perform critical tasks that used to require IP header data, such as identifying LSAs, which distribute routing data, OSPFv3 utilizes network-protocol-independent information.

In addition to changing header data, OSPFv3 redefines the roles its LSAs play.

In OSPFv3, the tasks of advertising network topology and IPv6 data are divided among new and existing LSAs.

For example, OSPFv3's network and router LSAs no longer distribute IP data; routers use them solely to discern network design. To advertise the data removed from these LSAs, OSPFv3 introduces two dedicated IPv6 messages, termed the Intra-Area-Prefix and Link LSAs. By reducing dependency on IPv6, OSPFv3's packet and LSA improvements enable easy support for new network protocols.

OSPFv3 is versatile enough to transcend IPv6 with minor network upgrades, instead of major protocol migrations.

To supplement its versatility, OSPFv3 increases the number of optional capabilities, such as multicast OSPF, that can be implemented. To achieve this, OSPFv3 expands the Options data field, which is used by network devices to advertise enabled capabilities. The Options field is contained in most OSPFv3 interrouter messages. Running OSPFv3, devices can support as many as 24 optional capabilities. Previous versions supported only eight.

To simplify the construction of complex fault-tolerant networks, OSPFv3 introduces Instance IDs and the R-bit option. As a component of every OSPFv3 packet header, Instance IDs can control communication between routers sharing a physical network and OSPF area, without relying on complex authentication schemes or access lists, as needed in the past. In addition to Instance IDs, OSPFv3 can bring effective redundancy to end systems, such as servers, with R-bit.

"The R-bit is a way for hosts to wiretap the routing protocol safely, participating in OSPFv3 without attracting nonlocal traffic," Moy says.

OSPFv3 ensures that future upgrades integrate smoothly with new mechanisms, including flooding scopes and handling options. Like a passport for LSAs, routers use flooding scopes to permit or deny travel across the net. The flooding scope's range limits every LSA (and, therefore, its effect on the network) to the local link, an area or the entire OSPFv3 network. Because routers can only enforce the flooding scope of readable LSAs, handling options are also incorporated into these messages. Handling options instruct routers to contain or forward undecipherable LSAs.

In OSPFv3, less security is definitely more. To simplify message structure, OSPFv3 breaks from the past by providing no inherent security. By relying on IPv6's integrated system of packet security subheaders, OSPFv3 messages can be authenticated and encrypted, a feat that previously required the addition of separate and complex protocols.

OSPFv3 offers increased capabilities, and it's so versatile that new network protocols can be easily supported. New features simplify network design and operation. With OSPFv3, the integration of updates will be less worrisome.

Finally, outdated portions of OSPFv3 have been removed, and its security has been boosted.

Giacalone is a principal consultant at Predictive Systems in New York, a network consulting firm focused on the design, management and security of large-scale networks. He can be reached at spencer.giacalone@ predictive.com.

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