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 9.1.1.0 through 9.1.1.255 (the
9.1.1.0/255.255.255.0 subnet) while another can represent addresses
from 9.2.0.0 through 9.2.255.255 (the 9.2.0.0/255.255.0.0 subnet).
- IPv6 RIP
- 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
- 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| Feature |
RIP-1 |
RIP-2 |
IPv6 RIP |
OSPF |
IPv6 OSPF |
|---|
| 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 |
Notes: - Depends on network size and stability.
- 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.
- RIP in OMPROUTE allows multiple equal-cost routes only for directly
connected destinations over redundant interfaces. See Use of static routing with OMPROUTE.
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