Advanced Computer Networks CS716 Advanced Computer Networks By Dr. Amir Qayyum 1
Lecture No. 19
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
Datagram Forwarding Network Number Next Hop 1 R3 2 R1 3 Interface 1 4
Datagram Forwarding Network # Netmask Next Hop/Port 18.0.0.0 255.0.0.0 1 128.32.0.0 255.255.0.0 2 0.0.0.0 0.0.0.0 3 dest: 18.26.10.0 mask with 255.0.0.0 matched! send to port 1 dest: 128.16.14.0 mask with 255.0.0.0 not matched mask with 255.255.0.0 not matched mask with 0.0.0.0 matched! send to port 3
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
ARP in ATM
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
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)
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
DHCP Server Unicast to server DHCP DHCP Other networks relay server Broadcast Host