Lecture 17 November 8Intra-domain routing November 13Internet routing 1 November 15Internet routing 2 November 20End-to-end protocols 1 November 22End-to-end protocols 2 November 27End-to-end protocols 3 November 29Exam 4 December 8Exam 5 and Final

Routing versus Forwarding Network Number InterfaceMAC Address 10if08:0:2b:e4:b:1:2 Network NumberNext Hop Routing Table: Forwarding Table:

Why routing protocols? Link failures New nodes Congestion Two approaches: –Distance Vector-based on local information –Link State-based on global information

Distance-vector routing DestinationCostNext Hop B  B C  C D  C E1E F1F G  F

Routing Loops Example 1 –F detects that link to G has failed –F sets distance to G to infinity and sends update t o A –A sets distance to G to infinity since it uses F to reach G –A receives periodic update from C with 2-hop path to G –A sets distance to G to 3 and sends update to F –F decides it can reach G in 4 hops via A Example 2 –link from A to E fails –A advertises distance of infinity to E –B and C advertise a distance of 2 to E –B decides it can reach E in 3 hops; advertises this to A –A decides it can read E in 4 hops; advertises this to C –C decides that it can reach E in 5 hops…

Loop- Breaking Heuristics Set infinity to 16 Split horizon Split horizon with poison reverse

Router Information Protocol (RIP)

RIP packet

Link State Routing Each node establishes a list of directly connected neighbors and cost of each link Floods that information in a LSP to all neighbors Retransmits LSPs from other nodes- but does not echo to sender

Propagation of LSPs

LSP Information ID of sending node Link-state of sending node Sequence number Time to live

Route Calculation Each node has enough information to map the network Dijkstra’s shorted path algorithm used to compute the routes

Example: Link State Routing

Routing Table Calculation StepConfirmed TentativeComments

Routing Table Calculation StepConfirmedTentativeComments 5 6

Routing Table Calculation StepConfirmedTentativeComments 7

OSPF Authentication Hierarchy-Domains and Areas Load Balancing

OSPF Header Format

OSPF link-state advertisement

Metrics Issues –Number of Hops –Latency –Bandwidth or Capacity –Congestion Difficult to assign a scalar cost to such a complex and changing problem

ARPANET 1 Lowest Cost=Shortest Queue

ARPANET 2 Delay=(Depart time-Arrival Time)+Transmission Time+Latency Reliability incorporated through the Depart Time parameter Wide spread of weights- Oscillations

ARPANET 3 Reduce dynamic range of metric Averaging Hard limit on changes in metric-like the stock market