Overview: IP

• header
• fragmentation and reassembly
• IPv6
• mobile IP
• ICMP
• DHCP
• SLIP
• PPP

IP Header

IP fragmentation

• IP packets cannot be larger than Maximum Transmission Unit (MTU) of underlying network
• many different networks in Internet
• router may be given packet of size N to send over network with MTU < N
• put "unique" identifier in each packet
• fragmentation may also be done by sender

IP reassembly

• ID identifies packet
• offset * 8 identifies fragment within packet
• flags identify end of packet (last fragment)

• packets, fragments may be delivered out of order
• use TTL to discard packets with lost fragments

IPv6

• design initiated in response to exhaustion of class B addresses
• 128-bit addresses
• better autoconfiguration
• better security (encryption, authentication)
• better type of service
• simpler to process a packet
• no header checksum
• "extension headers" instead of options, higher-level protocols

ICMP

• Internet Control Message Protocol
• ping
• try to inform sender when discarding a packet
• (never send in response to an ICMP packet)
• unreliable, but useful

Mobile IP

• post office forwarding address
• I get a guest IP address from the network I'm on
• forwarding agent on my network sends all my packets to the guest address
• I can either
  • send packets with my home IP address (probably dropped for security reasons)
  • send packets with my guest IP address (source address authentication won't work)

DHCP

• Dynamic Host Configuration Protocol
• "plug and play"
• broadcast request for IP address
• assigned IP address
• e.g. ISPs

PPP

• "lower layer" for IP (and other protocols)
• has IP address negotiation
• can use multiple serial lines
• 2-byte CRC
• complex, useful

SLIP

• "lower layer" for IP only
• marker character END, replaced in packet by ESC END
• escape character ESC, replaced in packet by ESC ESC
• END starts and ends packet
• IP+TCP headers are predictable: compression increases rate of useful data