CSEE W4140
Networking Laboratory
Lecture 3: IP Forwarding and ICMP
Jong Yul Kim
02.04.2009
IP in Internet Protocol StackApplication
TCP
UDP
ICMP
IP
ARP
Network
Access
IGMP
Transport
Layer
Transport
Network
Network
Layer
Link
Link Layer
Media
Physical
IP network
10.0.1.11
128.59.16.1
Two functions of network layer
 Routing
“Collective interactions of all routers to
determine the paths that packets take on
their trips from source to destination”
 Forwarding
“The transfer of a packet from an incoming
link to an outgoing link within a single
router.”
Today’s topics
Subnet (RFC 950)
 Hard to define…
 General recipe
“Detach each interface from its host or
router, creating islands of isolated
networks, with interfaces terminating the
end points of the isolated networks.
Each of these isolated networks is called
a subnet.”
Subnet Exercise 1
Subnet Exercise 2
Netmask
 Hosts and routers within a subnet use
netmask to determine whether the
other host is directly connected or not
Classless Interdomain Routing
(RFC 4632)
 Examples
 128.59.19.10
 One host on CS net
 128.59.16.0/21  CS wired net
 128.59.0.0/16  Columbia wired net
 Two parts to an address
 Network part (first 21 bits of CS wired)
 Host part (remaining 11 bits)
IPv4 Datagram Format (RFC 791)
Router Architecture
Processor
Memory
CPU
Interconnection Network
Interface Card
Interface Card
Interface Card
Functional Components
routing
protocol
Routing
functions
routing
protocol
forwarding table
updates
Control
forwarding
table
Datapath:
forwardng table
lookup
incoming IP
datagrams
IP
Forwarding
per-packet
processing
outgoing IP
datagrams
Forwarding Table
Destination
10.1.0.0/24
10.1.2.0/24
10.2.1.0/24
10.3.1.0/24
20.1.0.0/16
20.2.1.0/28
Next
Hop
direct
direct
R4
direct
R4
R4
IP datagrams can be directly delivered
(“direct”) or are sent to a router (“R4”)
Delivery with forwarding tables
to:
20.2.1.2
Longest Prefix Matching Rule
Destination
Next Hop
11001000
11011111
200.223.0.0/16
200.16.0.0/13
11001000
00010
200.22.0.0/15
11001000
0001011
R2
R4
Direct
 Where would this packet go?
Packet destination is: 200.23.146.51
11001000 00010111 10010010 00110011
ICMP (RFC 792)

Used to communicate network info



Error reporting
Router advertisement and discovery
Has type and code


Type 8, code 0 = echo request
Type 0, code 0 = echo reply

Replies have original sender’s IP header + 64 bits of data

Used by


ping
traceroute
IOS Command Mode Hierarchy
Read the Introduction part 4 in textbook
Main Points of Lab 3
 Setting up static routes on:
 Linux machines
 Cisco routers
 Routing packets using:
 Proxy ARP
 ICMP Route Redirect
 Netmasks
Kermit not used  use picocom!
Homework
 Prelab 3 due on Friday (02.06.2009)
 Lab report 2 due by beginning of
lab 3 next week
 Read
 RFC 2453 “RIP Version 2” parts 1 ~ 3
Announcements
 In-class quiz next week
 Basic ARP, subnets, and IP forwarding
 Swipe Access
 Apar, Hai, Eric, Aaron, Abhinav
 Please check on Monday