1. Advanced Computer Networks
CS716
Advanced Computer Networks
By Dr. Amir Qayyum 1

2. Lecture No. 19

3. Fragmentation and Reassembly Example
Ident
= x
Offset
= 0
Start of header 1
Rest of header
512 data bytes
= 64
= 128
376 data bytes
Ident
= x
Offset
= 0
Start of header
Rest of header
1400 data bytes

4. Datagram Forwarding Network Number Next Hop 1 R3 2 R1 3 Interface 1 4

5. Datagram Forwarding Network # Netmask Next Hop/Port
dest:
mask with
matched! send to port 1
dest:
mask with
not matched
mask with
not matched
mask with
matched! send to port 3

6. ARP Packet Format T argetHardwareAddr (bytes 2 – 5)
argetProtocolAddr (bytes 0 3)
SourceProtocolAddr (bytes 2
Hardware type = 1
Protocol
Type = 0x0800
SourceHardwareAddr (bytes 4
argetHardwareAddr (bytes 0 1)
SourceProtocolAddr (bytes 0
HLen = 48
PLen = 32
Operation
SourceHardwareAddr (bytes 0 8 16 31

7. ARP in ATM

8. Internet Control Message Protocol (ICMP)
IP companion protocol (not necessary)
Handles error and control messages
FTP
HTTP NV
TFTP
TCP
UDP IP
ICMP …
FDDI
Ethernet
ATM

9. ICMP Message
Sent to the source when a node is unable to process IP datagram successfully
Error messages
Destination unreachable (protocol, port, or host)
Reassembly failed
IP Checksum failed; or invalid header
TTL exceeded (so datagrams don’t cycle forever)
Cannot fragment
Control messages
Echo (ping) request and reply
Redirect (from router to source host, to change route)

10. Dynamic Host Configuration Protocol- DHCP
DHCP server is required to provide configuration information to each host
Each host retrieve this information on bootup
DHCP server can be configured manually, or it may allocate addresses on-demand
Addresses are “leased” for some period of time
Each host is not configured for DHCP server, it performs a DHCP server discovery
A broadcast discovery message is sent by the host and a unicast reply is sent by the server

11. DHCP Server Unicast to server DHCP DHCP Other networks relay server
Broadcast
Host