Advanced Computer Networks: Lecture 19. This lecture will cover the following: fragmentation and reassembly example; datagram forwarding; ARP packet format; internet control message protocol (ICMP); dynamic host configuration protocol- DHCP; DHCP server discovery;...
CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 19 Fragmentation and Reassembly Example H1 R1 R2 R3 H8 Start of header Ident= x Offset= Rest of header ETH IP (1400) FDDI IP (1400) PPP IP (512) ETH IP (512) PPP IP (512) ETH IP (512) PPP IP (376) ETH IP (376) 512 data bytes Start of header Ident= x Offset= 64 Rest of header 512 data bytes Start of header Ident= x Offset= Rest of header 1400 data bytes Start of header Ident= x Offset= 128 Rest of header 376 data bytes Datagram Forwarding Network Number Next Hop R3 R1 Interface 1 Interface 0 Datagram Forwarding Network # Netmask 18.0.0.0 128.32.0.0 0.0.0.0 255.0.0.0 255.255.0.0 0.0.0.0 dest: 18.26.10.0 mask with 255.0.0.0 Next Hop/Port 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 matched! send to port 3 mask with 0.0.0.0 ARP Packet Format 16 Hardware type = HLen = 48 31 Protocol PLen = 32 Type = 0x0800 Operation SourceHardwareAddr (bytes – 3) SourceHardwareAddr (bytes – 5) SourceProtocolAddr (bytes – 1) SourceProtocolAddr (bytes – 3) TargetHardwareAddr (bytes – 1) TargetHardwareAddr (bytes TargetProtocolAddr (bytes – 5) – 3) ARP in ATM 10.0.0.2 H1 R 12.0.0.3 10.0.0.1 12.0.0.5 H2 LIS 10 LIS 12 ATM network Internet Control Message Protocol (ICMP) • IP companion protocol (not necessary) • Handles error and control messages FTP HTTP NV TFTP UDP TCP ICMP IP 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 ondemand – 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 10 and a unicast reply is sent by the server DHCP Server Unicast to server Broadcast DHCP relay Other networks DHCP server Host 11 .. .Lecture? ?No.? ?19 Fragmentation and Reassembly Example H1 R1 R2 R3 H8 Start of header Ident= x Offset= Rest