Interior Gateway Protocols

An interior gateway protocol (IGP) is a dynamic route update protocol used between routers that run on TCP/IP hosts within a single autonomous system. The routers use this protocol to exchange information about IP routes.

Some of the more common interior gateway protocols are:
Routing Information Protocol (RIP)
RIP uses a distance vector algorithm to calculate the best path to a destination based on the number of hops in the path. RIP has several limitations. Some of the limitations which exist in RIP Version 1 are resolved by RIP Version 2.
RIP Version 2
RIP Version 2 extends RIP Version 1. Among the improvements are support for multicasting and variable subnetting. Variable subnetting allows the division of networks into variable size subnets. For example, one route can represent addresses from through (the subnet) while another can represent addresses from through (the subnet).
IPv6 RIP uses the same distance vector algorithm used by RIP to calculate the best path to a destination. It is intended to allow routers to exchange information for computing routes through an IPv6-based network.
Open Shortest Path First (OSPF)
OSPF uses a link state or shortest path first algorithm. OSPF's most significant advantage compared to RIP is the reduced time needed to converge after a network change. In general, OSPF is more complicated to configure than RIP and might not be suitable for small networks.
IPv6 OSPF also uses a link state or shortest path first algorithm to calculate the best path to a destination. IPv6 OSPF has the same advantages and more complicated configuration compared to IPv6 RIP, like OSPF compared to RIP.
Table 1. Interior Gateway Protocol characteristics
Algorithm Distance vector Distance vector Distance vector Shortest path first Shortest path first
Network load (1) High High High Low Low
CPU processing requirement (1) Low Low Low High High
IP network design restrictions Many Some Some Virtually none Virtually none
Convergence time Up to 180 seconds Up to 180 seconds Up to 180 seconds Low Low
Multicast supported (2) No Yes Yes Yes Yes
Multiple equal-cost routes No (3) No(3) No(3) Yes Yes
  1. Depends on network size and stability.
  2. Multicast saves CPU cycles on hosts that are not interested in certain periodic updates, such as OSPF link state advertisements or RIP-2 routing table updates. Multicast frames are filtered out either in the device driver or directly on the interface card if this host has not joined the specific multicast group.
  3. RIP in OMPROUTE allows multiple equal-cost routes only for directly connected destinations over redundant interfaces. See Use of static routing with OMPROUTE.