Introduction to IPv6 (Chapter 4 in Huitema) IPv6,Mobility-1 S-38.2121 / Fall-2006 / N Beijar IPv6 addresses • 128 bits long • Written as eight 16-bit hexadecimal integers separated with colons – E.g. 1080:0000:0000:0000:0000:0008:200C:417A = 1080::8:800:200C:417A • Types – Unicast • Defines one interface within their scope of validity – Multicast • Delivers packets to all members of a group – Anycast • Delivers packets to the nearest member of a group IPv6,Mobility-2 S-38.2121 / Fall-2006 / N Beijar
Special IPv6 addresses • Unspecified = 0:0:0:0:0:0:0:0 = :: – Only as source address • Loopback = 0:0:0:0:0:0:0:1 = ::1 – For sending datagrams to itself • IPv4 addresses prepended with zeroes – 0:0:0:0:0:0:AABB:CCDD = ::a.b.c.d • Site-local addresses – FEC0:0000:0000:subnet:station (subnet 16 bits, station 64 bits) • Link-local addresses (not relayed by router) – FEB0:0000:0000:0000:station IPv6,Mobility-3 S-38.2121 / Fall-2006 / N Beijar IPv6 header Version=6 (4) Traffic class (8) Flow label (24 bits) Version=6 (4) Traffic class (8) Flow label (24 bits) Payload length (16 bits) Next header type (8) Hop limit (8) Payload length (16 bits) Next header type (8) Hop limit (8) Source address (128 bits) Source address (128 bits) Destination address (128 bits) Destination address (128 bits) • Differences between v4 and v6 – No checksum (performed by lower layers) – No fragmentation (path MTU discovery instead, min. 1280 bytes) – No options (fixed length header, options in linked extension headers instead) • Extension headers replace options IPv6 header Extension Extension Payload (TCP) NH NH NH IPv6 header Extension Extension Payload (TCP) IPv6,Mobility-4 S-38.2121 / Fall-2006 / N Beijar
Source routing is implemented with the routing header • Routing header: Next header Header ext. length Routing type = 0 Segments left Next header Header ext. length Routing type = 0 Segments left Reserved Reserved IPv6 address 1 IPv6 address 1 IPv6 address 2 IPv6 address 2 . . . . . . IPv6 address N IPv6 address N • Only the router whose address is destination address in IPv6 header examines this extension ÿ better performance • Forwarder – Swaps the next address in the list and the destination address of the header Can be replaced by IP-in-IP – Decrements the number of segments left IPv6,Mobility-5 S-38.2121 / Fall-2006 / N Beijar Only the sender can fragment packets • No fragmentation in routers – Packets larger than the next hop’s MTU are rejected, and ICMP message sent back • Large packets (e.g. in UDP) must be fragmented by the sender • Fragment header: Hext header Reserved Fragment offset Reserved M Hext header Reserved Fragment offset Reserved M Identification Identification More fragments Most significant (M=1 in all 13 bits of 16-bit packets but word the last) IPv6,Mobility-6 S-38.2121 / Fall-2006 / N Beijar
Other extensions • Authentication Header (AH) for authentication • Encrypted Security Payload (ESP) for authentication + encryption • Destination options header is only examined by the destination – Contains one or several options – Also defines handling for unrecognized parameters • Ignore / discard silently / discard and send ICMP message • Hop-by-hop options header is examined by each router – Similar format and coding as destination options header – E.g. jumbo payload • Processing order is important – IPv6 ÿ Hop-by-hop options ÿ Destination options (for endpoint of tunnel) ÿ Routing ÿ Fragment ÿ Authentication ÿ Destination options (for destination) ÿ Upper layers (TCP/UDP) IPv6,Mobility-7 S-38.2121 / Fall-2006 / N Beijar Internet Control Message Protocol Version 6 ICMPv6 header: Type Code Checksum Type Code Checksum ICMP body ICMP body ICMP message types: 1. Destination unreachable 2. Packet too big errors 3. Time exceeded 4. Parameter problem 128. Echo request � Also includes the for ”ping” 129. Echo reply functionalities of 133. Router solicitation IGMP and ARP 134. Router advertisement router discovery 137. Redirect IPv6,Mobility-8 S-38.2121 / Fall-2006 / N Beijar
Router advertisements are sent by routers • For building a local list of routers on the same network Suggestion for initial Seconds for holding in hop limit value router list Type = 134 Code = 0 Checksum Type = 134 Code = 0 Checksum Cur. hop limit M O Res. Router lifetime Cur. hop limit M O Res. Router lifetime Reachable time Reachable time Retransmission timer Retransmission timer Options (e.g. source link layer option, MTU option) Options (e.g. source link layer option, MTU option) Interval between Expected time neighbors Source Link Layer successive solicitations of remain reachable after option: contains a neighbor that is not advertising their media media address of returning solicited address (in milliseconds) router neighbor advertisements IPv6,Mobility-9 S-38.2121 / Fall-2006 / N Beijar Neighbor discovery finds the MAC address corresponding to the IP address of the next hop neighbor solicitation (comp. ARP-request): Type = 135 Code = 0 Checksum Type = 135 Code = 0 Checksum R S O Reserved R S O Reserved Solicited address Solicited address Source link-level address option ÿ own MAC address Source link-level address option ÿ own MAC address MAC address ÿ solicited node multicast address = FF02:0:0:0:0:1 + last 32 bits of address No in cache? neighbor advertisement (comp. ARP-reply): R=1 if address Type = 136 Code = 0 Checksum is router, Type = 136 Code = 0 Checksum S=1 reply to R S O Reserved R S O Reserved solicitation, Solicited address Solicited address O=1 overrides Link layer address option ÿ found MAC address previous entry Link layer address option ÿ found MAC address My IP address Yes in solicitaition? IPv6,Mobility-11 S-38.2121 / Fall-2006 / N Beijar
Redirect works like in IPv4 but may include the media address of the next hop • Redirect message: Type = 137 Code = 0 Checksum Type = 137 Code = 0 Checksum Reserved Reserved Target address Target address Destination address Destination address Options (e.g. target link layer address, redirected header option) Options (e.g. target link layer address, redirected header option) Target address contains The media address of the next hop the better next hop for the may be included in a target link destination layer address option. IPv6,Mobility-12 S-38.2121 / Fall-2006 / N Beijar The sender needs feedback from the destination so that it does not send to a ”black hole” • If the sender does not get feedback (e.g. TCP acks) within 30 seconds, it checks the existence of the receiver with a solicitation message solicitation solicitated advertisement update cache update cache solicitation destination unreachable solicitation (to application) solicitation remove from cache remove from cache calculate new next-hops calculate new next-hops IPv6,Mobility-13 S-38.2121 / Fall-2006 / N Beijar
Before obtaining an address with autoconfiguration, the host uses a link local address • FEB0:0000:0000:0000 + EUI-64 identifier • The 64-bit EUI-64 identifier is generated from the 48-bit Ethernet address • The host must check that the link local address is unique – In principle, addresses generated with the EUI-64 identifier should be unique, but... solicitation solicitation solicitated advertisement 1 s address not unique address not unique address is unique ÿ pick another address is unique ÿ pick another • Lost messages ÿ retry several times IPv6,Mobility-14 S-38.2121 / Fall-2006 / N Beijar Autoconfiguration can be stateful or stateless new hostrouter solicitation [link-local-address ÿ all-routers] router Type = 133 Code = 0 Checksum Type = 133 Code = 0 Checksum Reserved Reserved Options.... (link layer address) Options.... (link layer address) router advertisement [ ÿ all-hosts / ÿ link-local-address] Type = 134 Code = 0 Checksum Type = 134 Code = 0 Checksum Hop.limit M O O Res. Router lifetime Hop.limit M Res. Router lifetime Reachable time Reachable time Retransmission timer Retransmission timer Options.... (prefix information option) Options.... (prefix information option) Stateful auto- M=1 stateful conf. with conf.server M=1 configuration stateful conf. with conf.server yes similar to DHCP O=1 obtain other parameters from conf.server O=1 obtain other parameters from conf.server yes in IPv4 stateless configuration stateless configuration IPv6,Mobility-15 S-38.2121 / Fall-2006 / N Beijar
Stateless autoconfiguration Type = 134 Code = 0 Checksum Type = 134 Code = 0 Checksum Contains list of prefixes with Hop.limit M O O Res. Router lifetime Hop.limit M Res. Router lifetime parameters Reachable time Reachable time • on-link bit ÿ the prefix is specific Retransmission timer Retransmission timer to the local link Options.... ( prefix information option ) Options.... ( prefix information option ) • autonomous-bit ÿ host can construct address by replacing the last bits of the prefix with EUI-64 identifier Properties • simple, no servers required • inefficient: 64 bits used for one local network • no access control IPv6,Mobility-16 S-38.2121 / Fall-2006 / N Beijar Mobile IP (Chapter 13 in Huitema) IPv6,Mobility-17 S-38.2121 / Fall-2006 / N Beijar
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