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2.1 | |
Link-State Routing Protocol | |
| 2.1.6 | |
Compare and contrast distance vector and link-state routing |
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All distance vector protocols learn
routes and then send these routes to directly connected neighbors.
However, link-state routers advertise the states of their links to all
other routers in the area so that each router can build a complete link-state database. These advertisements are called link-state
advertisements (LSAs). Unlike distance vector routers, link-state
routers can form special relationships with their neighbors and other
link-state routers. This is to ensure that the LSA information is
properly and efficiently exchanged. The initial flood of LSAs provides
routers with the information that they need to build a link-state
database. Routing updates occur only when the network changes. If
there is no changes,
the routing updates occur after a specific interval. If the network
changes, a partial update is sent immediately. The partial update
only contains contains information about links that have changed, not a complete routing
table. An administrator concerned about WAN link utilization will find
these partial and infrequent updates an efficient alternative to
distance vector routing, which sends out a complete routing table every
30 seconds. When a change occurs, link-state routers are all
notified simultaneously by the partial update. Distance vector routers
wait for neighbors to note the change, implement the change, and then
pass it to the neighboring routers.
The benefits of link-state routing over distance vector protocols include faster convergence and improved bandwidth utilization. Link-state protocols support classless interdomain routing (CIDR) and variable-length subnet mask (VLSM). This makes them a good choice for complex, scalable networks. In fact, link-state protocols generally outperform distance vector protocols on any size network. Link-state protocols are not implemented on every network because they require more memory and processing power than distance vector protocols and can overwhelm slower equipment. Another reason they are not more widely implemented is the fact that link-state protocols are quite complex. This would require well-trained administrators to correctly configure and maintain them.
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