Dynamic routing • Routing Algorithm (Dijkstra / Bellman-Ford) – idealization – All routers are identical – Network is flat. • Not true in Practice • Hierarchical routing – Internet = network of networks – Each network admin may want to control routing in its own routing network. – Hierarchical routing solves • Scale problems. • Administrative autonomy.
Routing Protocols RIP, OSPF, BGP • Dynamic protocols – • • • • Sharing neighborhood information Use different metrics. RIP (one hop count, how many networks a packet crosses), Networks are treated equally BGP (depend on the policy, set by administrator) OSPF (TOS, minimize delay, maximize throughput)
Routing Information Protocol RFC 1058 • • • • • • http://www.faqs.org/rfcs/rfc1058.html Distance vector algorithm (Bellman-Ford) – Sharing knowledge about the entire AS – Shares only with neighbors – Shares at regular intervals (different from DVA) Receive a RIP message (a response) Add one hop for each advertised dest Repeat • If (dest not in routing table) • Add the advertised info to the table • Else • If (next-hop is the same) • Replace with the advertised one • Else • If (advertised hop count < one in the table) • Replace entry in the routing table Return
Initializing and Updating Routing Table • • Destination Dest • • Rule to implement RIP based in DVA If Information is not from G – • Metric D Update to reflect minimum cost If Information is from G – Always update Gateway G