Lecture CS496 06 W0708
11/30/2007
1
IP Routing
Routing Selecting the path of travel IP Forwarding Basics of choosing the path Route Discovery Learning paths [Later]
2
Choosing a Path
Packet considerations Network load Packet length g Service request Often not considered Destination considerations Direct delivery (same LAN) Indirect delivery (another LAN)
3
Direct Delivery
Determine locality Compare my NetID to destination NetID Use local Net Mask Determine NIC/MAC address Use ARP or similar Encapsulate Send
2004-2007 by Henry L. Welch
1
CS496 Lecture 06 W0708
11/30/2007
4
Indirect Delivery
Issues to consider Current NetID vs. Destination NetID How much of the intervening WAN must we know? How do we store this information?
5
Next Hop Routing Tables
Common solution Only store the next hop in the path Use a simple look-up table lookKey via NetID prefix Subject to classless rules Return the IP of the next router
6
Routing Table Options
Default routers Optimization If no entry found send to a default router Common for gateways Host specific paths Administration Force local routes to take
2004-2007 by Henry L. Welch
2
CS496 Lecture 06 W0708
11/30/2007
7
Datagram Alteration
Only two changes needed Decrement hop counter checksum ReRe-compute No other alteration needed Source and destination are ALWAYS fixed by sender Routers are NOT destinations
8
Ancillary Operations
Error reporting Hop count expiration No routing table entry Congestion Drop and notify Route learning [Later]
9
Sockets
Communication abstraction Often applied to TCP Transport Layer Designed for secure delivery ConnectionConnection-based protocol Sender and receiver establish a link Transmit data Acknowledge error-free reception error-
2004-2007 by Henry L. Welch
3
CS496 Lecture 06 W0708
11/30/2007
10
Socket Client
1. 2.
3.
4.
Create a socket Specify a server via IP and port# They establish a connection y Read/Write data It can be both ways or only one (half-closed) (halfClo...