COMPUTER NETWORKS CS610 Lecture-32 Hammad Khalid Khan

Review Lecture 31  Success of IP  Motivation for Change  IPV6 Features  IPV6 Datagram Format  IPV6 Base Header Format  Parsing IPV6 Headers

Fragmentation  Fragmentation information kept in separate extension header  Each fragment has base header and (inserted) fragmentation header  Entire datagram, including original header may be fragmented

Fragmentation

Fragmentation and Path MTU  IPv6 source (not intermediate routers) responsible for fragmentation – Routers simply drop datagrams larger than network MTU – Source must fragment datagram to reach destination  Source determines path MTU – Smallest MTU on any network between source and destination – Fragments datagram to fit within that MTU

Fragmentation and Path MTU  Uses path MTU discovery – Source sends probe message of various sizes until destination reached – Must be dynamic - path may change during transmission of datagrams

Use of Multiple Headers  Efficiency - header only as large as necessary   Flexibility - can add new headers for new features  Incremental development - can add processing for new features to testbed; other routers will skip those headers

IPv6 Addressing  128-bit addresses  Includes network prefix and host suffix  No address classes - prefix/suffix boundary can fall anywhere

IPv6 Addressing  Special types of addresses: – Unicast - single destination computer – Multicast - multiple destinations; possibly not at same site – Cluster - collection of computers with same prefix; datagram is delivered to one out of cluster

IPv6 Address Notation  128-bit addresses unwidely in dotted decimal; requires 16 numbers   Groups of 16-bit numbers in hex separated by colons - colon hexadecimal (or colon hex)  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  FF0C::B1  IPv6 address with 96 leading zeros is interpreted to hold an IPv4 address

Chapter 23 An Error Reporting Mechanism (ICMP)

Introduction  IP provides best-effort delivery   Delivery problems can be ignored; datagrams can be "dropped on the floor"  Internet Control Message Protocol (ICMP) provides error- reporting mechanism

Best-Effort Semantics and Error Detection  Internet layer can detect a variety of errors: – Checksum (header only!) – TTL expires – No route to destination network – Can't deliver to destination host (e.g., no ARP reply)  Internet layer discards datagrams with problems  Some - e.g., checksum error - can't trigger error messages

Internet Control Message Protocol  Some errors can be reported – Router sends message back to source in datagram – Message contains information about problem  Encapsulated in IP datagram

Types of Messages  Internet Control Message Protocol (ICMP) defines Error and Informational messages  Error messages: – Source quench – Time exceeded – Destination unreachable – Redirect – Fragmentation required

Types of Messages  Informational messages: – Echo request/reply – Address mask request/reply – Router discovery

Summary  Fragmentation in IPV6  Use of Multiple Headers  IPV6 Addressing  ICMP  Best Effort Semantics and Error Detection  Types of ICMP Messages