Understanding Routing
Routing Protocols
Routed versus Routing Protocols
Confusion often exists between the similar terms routing protocol
and routed protocol. Routed protocols are any network protocol suite that provides
enough information in its network layer address to allow a packet to direct user
traffic. Routed protocols define the format and use of the fields within a packet.
Packets generally are conveyed from end system to end system. The Internet IP
protocol and Novell’s IPX are examples of routed protocols. Other examples
include DECnet, AppleTalk, Novell NetWare, Open Systems Interconnect (OSI), Banyan
VINES, and Xerox Network System (XNS).
A routing protocol supports a routed protocol by providing
mechanisms for sharing routing information. Routing protocol messages move between
the routers. A routing protocol allows the routers to communicate with other routers
to update and maintain tables. Routing protocol messages do not carry end-user
traffic from network to network. A routing protocol uses the routed protocol to
pass information between routers. TCP/IP examples of routing protocols are the
Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP),
Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Enhanced IGRP
(EIGRP).
Routing Protocol Evolutions
Distance Vector
RIP - Routing Information Protocol. The most common IGP in
the Internet. RIP uses hop count as a routing metric.
IGRP - Interior Gateway Routing Protocol. IGP developed by
Cisco to address the issues associated with routing in large,
heterogeneous networks.
Link State
OSPF - Open Shortest Path First. Link-state, hierarchical
IGP routing algorithm proposed as a successor to RIP in the
Internet community. OSPF features include least-cost routing,
multipath routing, and load balancing. OSPF was derived from
an early version of the IS-IS protocol.
NLSP - NetWare Link Services Protocol. Link-state routing
protocol based on IS-IS.
IS-IS - Intermediate System-to-Intermediate System. OSI link-state
hierarchical routing protocol based on DECnet Phase V routing,
whereby ISs (routers) exchange routing information based on
a single metric, to determine network topology.
Hybrid
EIGRP - Enhanced Interior Gateway Routing Protocol. Advanced
version of IGRP developed by Cisco. Provides superior convergence
properties and operating efficiency, and combines the advantages
of link state protocols with those of distance vector protocols.
RIP and IGRP
RIP takes the path with the least number
of hops, but does not account for the speed of the links.
It only counts hops. The limitation of RIP is about 15 hops.
This creates a scalability issue when routing in large, heterogeneous
networks.
IGRP was developed by Cisco and works only with Cisco products
(although it has been licensed to some other vendors). It
accounts for the varying speeds of each link. Additionally,
IRGP can handle 224 to 252 hops, depending on the IOS version.
However, IGRP only supports IP.
OSPF and EIGRP
OSPF - Open Shortest Path First. Link-state,
hierarchical IGP routing algorithm proposed as a successor
to RIP in the Internet community. OSPF features include least-cost
routing, multipath routing, and load balancing. OSPF was derived
from an early version of the IS-IS protocol.
EIGRP - Enhanced Interior Gateway Routing Protocol. Advanced
version of IGRP developed by Cisco. Provides superior convergence
properties and operating efficiency, and combines the advantages
of link state protocols with those of distance vector protocols.
Related Topics
- Summary -
- Routers move data across networks
from a source to a destination
- Routers determine the optimal path for forwarding
network traffic
- Routing protocols communicate reachability information
between routers
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