Network Layer: IPv6 IS250 Spring 2010

John Chuang2 IPv6 (RFC 2460)  Motivations -Shortage of IP addresses -Native support for multicast, anycast, security, mobility, QoS, etc.  Highlights -128 bit addresses -Extension headers for protocol extensibility

John Chuang3 IPv6 Datagram

John Chuang4 Base Header Format  Base header is 40 bytes in length (fixed)  Contains less information than IPv4 header -Exception: FLOW LABEL used to associate datagrams belonging to a flow between two end-hosts

John Chuang5 Extension Headers  Base header is fixed size (40 Bytes) -NEXT HEADER field in base header defines type of header  Extension headers are variable sized -NEXT HEADER field in extension header defines type -HEADER LEN field gives size of extension header

John Chuang6 IPv6 Fragmentation  Fragmentation supported via extension header (i.e., fragmentation header)  Sender responsible for fragmentation -Routers simply drop datagrams larger than network MTU  Source must fragment datagram to reach destination -Source must determine path MTU, i.e., minimum MTU between source and destination  Path MTU discovery -Source sends probe message of various sizes until destination reached -Must be dynamic - path may change during transmission of datagrams

John Chuang7 IPv6 Addressing  128-bit addresses  Includes network prefix and host suffix  No address classes - prefix/suffix boundary can fall anywhere  Special types of addresses: -unicast - single destination computer -multicast - multiple destinations -anycast - collection of computers with same prefix; datagram is delivered to any one computer within the collection (supports replication of services)

John Chuang8 IPv6 Address Notation  128-bit addresses unwieldy in dotted decimal; requires 16 numbers  Groups of 16-bit numbers in hexadecimal (base 16) separated by colons - colon hexadecimal 69DC:8864:FFFF:FFFF:0:1280:8C0A:FFFF  Zero-compression - series of zeroes indicated by two colons FF0C:0:0:0:0:0:0:B1 same as FF0C::B1  IPv6 address with 96 leading zeros is interpreted to hold an IPv4 address

John Chuang9 Migrating to IPv6  Incremental deployability  Tunneling: Encapsulate IPv6 datagram in IPv4 datagram

John Chuang10 IPv6 Summary  IPv4 basic abstractions very successful  IPv6 carries forward many of those abstraction, but many details are changed -128-bit addresses -Base and extension headers -Source does fragmentation -Colon hexadecimal address notation  Migration to IPv6 is a challenge -Excess inertia due to network effects (Feb 2 lecture)