Chapter 5
The Network Layer
The IP Protocol
The IPv4 (Internet Protocol) header.
IP datagram format
IP protocol version
number 32 bits total datagram
header length head. type of length (bytes)
(bytes) ver length
len service for
“type” of data fragment fragmentation/
16-bit identifier flgs
offset reassembly
max number time to upper Internet
remaining hops live layer checksum
(decremented at
each router) 32 bit source IP address
upper layer protocol 32 bit destination IP address
to deliver payload to E.g. timestamp,
Options (if any)
record route
data taken, specify
(variable length, list of routers
typically a TCP to visit.
or UDP segment)
IP Addresses
IP address formats.
IP Addresses (2)
Special IP addresses.
Subnets
A campus network consisting of LANs for various departments.
Subnets (2)
A class B network subnetted into 64 subnets.
CDR – Classless InterDomain Routing
5-59
A set of IP address assignments.
NAT – Network Address Translation
Placement and operation of a NAT box.
The TCP Segment Header
TCP Header.
NAT – Network Address Translation
Placement and operation of a NAT box.
Internet Control Message Protocol
5-61
The principal ICMP message types.
ICMP: Internet Control Message Protocol
used
by hosts & routers to Type Code description
communicate network-level information 0 0 echo reply (ping)
error reporting: unreachable host, 3 0 dest. network unreachable
network, port, protocol 3 1 dest host unreachable
echo request/reply (used by ping) 3 2 dest protocol unreachable
3 3 dest port unreachable
network-layer “above” IP:
3 6 dest network unknown
ICMP msgs carried in IP datagrams 3 7 dest host unknown
ICMP message: type, code plus first 8 4 0 source quench (congestion
bytes of IP datagram causing error control - not used)
8 0 echo request (ping)
9 0 route advertisement
10 0 router discovery
11 0 TTL expired
12 0 bad IP header
Traceroute and ICMP
Source sends series of UDP segments to When ICMP message arrives, source
dest calculates RTT
First has TTL =1 Traceroute does this 3 times
Second has TTL=2, etc. Stopping criterion
Unlikely port number UDP segment eventually arrives at
When nth datagram arrives to nth router: destination host
Router discards datagram Destination returns ICMP “host
unreachable” packet (type 3, code 3)
And sends to source an ICMP
message (type 11, code 0) When source gets this ICMP, stops.
Message includes name of router&
IP address
ARP– The Address Resolution Protocol
Three interconnected /24 networks: two Ethernets and an FDDI ring.
Dynamic Host Configuration Protocol
Operation of DHCP.
The IP Protocol
The IPv4 (Internet Protocol) header.
The Main IPv6 Header
The IPv6 fixed header (required).
Extension Headers
5-69
IPv6 extension headers.
Extension Headers (2)
The hop-by-hop extension header for large datagrams (jumbograms).
Extension Headers (3)
The extension header for routing.