IGRP (Inter Gateway Routing Protocol):

Interior Gateway Routing Protocol (IGRP) is a distance vector routing protocol which is a proprietary and invented by Cisco. It is used by routers to exchange routing data within an autonomous system (AS). IGRP supports multiple metrics for routes, including bandwidth, load, delay and MTU. This improves reliability over RIP because IGRP uses advanced metrics to compare two routes into a combined route. The two routes together are combined into a single metric, using a formula which can be adjusted via command line. The maximum hop count of IGRP is 255 which is an improvement over RIPs 15 hop max. Keep in mind that IGRP is a Cisco proprietary protocol and can not be used in a mixed vendor network.

Link State: Link State routing protocol requires each router (peer) to maintain at least a partial map of the network. When a network link changes state (up to down, or vice versa), a notification, called a link state advertisement (LSA) is flooded throughout the network. All the routers note the change, and recompute their routes accordingly. This method is more reliable, easier to debug and less bandwidth-intensive than Distance-Vector. It is also more complex and more compute- and memory-intensive. Link state routing protocols are found in many lager networks and provide Scalable solutions for more complex networks.

OSPF (Open Shortest Path First):

Open shortest path first (OSPF) is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs) to all other routers within the same hierarchical area or autonomous system (AS). An AS can be divided into a number of areas, which are groups of contiguous networks and attached hosts. Information on attached interfaces, metrics used, and other variables are included in OSPF LSAs. As OSPF routers accumulate link-state information, they use the SPF algorithm to calculate the shortest path to each node.

(IS-IS) Intermediate System-to-Intermediate System:

Intermediate System-to-Intermediate System (IS-IS) is a routing protocol developed by the ISO and is natively an ISO Connectionless Network Service or CLNS protocol so it does not use IP to carry routing information messages. It uses OSI protocols to deliver its packets and establish its adjacencies. IS-IS has been enhanced to carry IP (Internet Protocol) and this is called Integrated IS-IS. Integrated IS-IS supports VLSM and converges rapidly. It is also scalable to support very large networks and is the key protocol in many larger ISP’s.

Hybrid: Hybrid routing Protocols are a combination or both Distance Vector and Link state protocols and only one protocol fits into this field. EIGRP is Cisco Systems Proprietary protocol based on their original IGRP. For more information on Hybrid Protocols look below to the section on “EIGRP”.

EIGRP (Enhanced Inter Gateway Routing Protocol):