Routing

Sunday, 18 May 2008 14:22

Router - Cisco Router

Static routing

Adds a static route to the routing table:

#(config) ip route [ipdest] [subnet] [next hop]

Distance Vector

Distance vector protocols use a vector of distance and direction to find the best path, where distance is defined in terms of a metric and direction is defined as the next-hop router. Distance vector protocols broadcast the entire routing table at periodic intervals and are slow to converge because of hold-down timers. Examples include RIP and IGRP.

Advertises all the known routes out off each interface.

• Route Poisioning – Gives a “down” route a infinite mectric “16” to show it is down.
• Split Horizon – Updates cannot be sent out the same interface that they came in on.
• Split Horizon with Poision Reverse – Failed Routes are given a infinite mectric but failed routes are advisted out the interface which the update came from.
• Hold-Down timer – When the router learns that a route has failed ignore any other update for that route for the certain period.

Triggered Updates – When a route fails it sends a flash update regarding the routes status.

Link State

Link-state protocols use a topological database that is created on each router. This database keeps track of directly attached neighbors, the entire network, and the routing table. Link-state updates are typically multicast to all neighbors. (OSPF is a link-state protocol.)