Many companies prefer to use protocols based upon standards whenever possible, which is strongly recommended in every network. Networks that are running today without the protocols in use having a proper standard will eventually cause problems. Either this could be network meltdown for no apparent reason, or you could become stranded on a technological desert islandjust you and your protocol.
OSPF is a standard protocol developed by a committee of the Internet Engineering Task Force (IETF) as an alternative to the RIP protocol. OSPF is defined in RFC 1583.
IS-IS is a standard protocol developed by the International Standards Organization (ISO OSI). IS-IS is defined in International Standard 10589. Integrated IS-IS is a standard extension to IS-IS developed by the Internet Engineering Task Force. Integrated IS-IS is defined in an Internet Draft.
Large networks being designed today do not have the luxury of assuming a single vendor environment. It is very common to have portions of a network that are provided by one vendor and other portions that are provided by another. In a perfect world, all network components would be supplied by one vendor.
You can use several techniques to permit multi-vendor environments. The most common technique is to use the same routing protocol on all of the routers.
RIP and OSPF are implemented by every major routing vendor.
Integrated IS-IS is implemented by most of the major router vendors.
Another common technique to permit multi-vendor environments is to use different routing protocols in different parts of the network and set up communication paths between the routing protocols. This technique enables a network designer to optimize each portion of the network for the characteristics that it requires. This technique also allows for the gradual migration of a network from one protocol to another and for the inclusion of equipment, which is not capable of supporting todays advanced protocols.
Cisco supports two techniques to enable communication between different routing protocols, redistribution and external routing protocols, as documented in the list that follows.
RIP has withstood the test of time. The future of RIP does not look that bright when compared to other solutions, but it is one of the most proven protocols available.
Integrated IS-IS has been available from Cisco for several years and is being deployed in a number of significant networks. IS-IS is the routing protocol of choice for networks that need to support both OSI and IP. Integrated IS-IS is the standard routing protocol for DECnet Phase V networks.
OSPF has been available for several years from all the major routing vendors and is being deployed in an increasing number of networks ranging from very simple to very complex.
This chapter discussed fundamental concepts of how to understand routing protocols. It has provided all types of routing table associations and discussed as well how a protocol algorithm is designed and what determines proper operation.
This chapter has also analyzed the differences between the two most important classes of protocols: distance vector and link state. Distance vector protocols use the distance (hops) to a destination as their metric, as demonstrated in RIP. A broad overview of RIP was provided on its operation and communication methods as a routing protocol. Link state protocols are a slightly more complex subject to understand. In order to assist in this understanding, the information provided was a bit more in-depth, and one of the more popular Internet routing protocols was used to demonstrate this routing protocol. IS-IS was used to provide the level of sophistication necessary.
Instead of debating the merits and lack thereof for each protocol, an entire section was dedicated to objectively analyzing and supporting the choice of a network protocol. It is also important to understand that sometimes being able to make a business successful is almost as important as being able to implement and design a network.