IPv6 Jyh-Cheng Chen Department of Computer Science and Institute - PDF document

IPv6 Jyh-Cheng Chen Department of Computer Science and Institute of Communications Engineering National Tsing Hua University jcchen@cs.nthu.edu.tw http://www.cs.nthu.edu.tw/~jcchen Outline IPv6 Header IPv6 Addressing IPv6 Neighbor Discovery IPv6 Autoconfiguration 2

Format of IPv4 Address 0 8 16 24 31 Class A netid hostid 0 Class B 1 0 netid hostid Class C 1 1 0 netid hostid Class D 1 1 1 0 multicast address Class E 1 1 1 1 reserved for future use 3 IPv4 Header 24 31 4 8 16 Ver IHL Service Type Total Length Identifier Flags Fragment Offset Time to Live Protocol Header Checksum 32 bit Source Address 32 bit Destination Address Options and Padding IHL: Internet Header Length 4

IPv6 Header 0 4 12 16 24 31 Version Traffic Class Flow Label Payload Length Next Header Hop Limit 128 bit Source Address 128 bit Destination Address 5 V6 vs. V4 Fields removed � IHL � Flags � Identification � Fragmentation offset � Header Checksum Field added � Flow Label 6

V6 vs. V4 (cont.) Fields renamed � Total Length -> Payload Length � Time to Live -> Hop Limit � Protocol -> Next Header � Service Type -> Traffic Class Field revised � 32-bit address to 128-bit address � Option: variable length replaced by extension header 7 IPv4 and IPv6 Packets maximum 65535 octets minimum 20 octets IPv4 Header Payload IPv4 maximum 65535 octets Fixed 0 or more 40 octets Extension Extension IPv6 Header Payload Header Header IPv6 8

Next Header Identify which header follows the basic IP header in the datagram Can indicate an optional IP header or an upper layer protocol The table in next page lists the mapping � Not a completed list 9 0 Hop-by-Hop Options Header 4 Internet Protocol 6 Transmission Control Protocol 17 User Datagram Protocol 43 Routing Header 44 Fragment Header 45 Interdomain Routing Protocol 46 Resource Reservation Protocol 50 Encapsulating Security Payload 51 Authentication Header 58 Internet Control Message Protocol 59 No Next Header 60 Destination Option Header 10

Vers. Class Flow Label Payload Length Next Header:0 Hop limit Source Address Destination Address Nxt Hdr:43 Hdr Length Hop-by-Hop Options Nxt Hdr:44 Hdr Length Routing Information Nxt Hdr:51 Reserved Fragment Offset M Fragment Identification Nxt Hdr:6 Hdr Length Authentication Data TCP Header and Data 11 Examples IPv6 header TCP header + data next header = TCP IPv6 header Routing header TCP header + data next header = next header = Routing TCP IPv6 header Routing header Fragment header fragment of TCP header + data next header = next header = next header = Routing Fragment TCP 12

IPv6 Extension Headers Compromise between generality and efficiency Support functions such as fragmentation, routing, authentication, etc. A sender can choose which extension headers to be included Intermediate routers only need to examine the hop-by-hop extension header � Only endpoints process other extension headers 13 Hop-by-Hop Specify delivery parameters at each hop on the path to the destination Header Extension Length � Number of 8-byte block in Hop-by-Hop header � Don’t include the first 8 bits Option � Type-Length-Value (TLV) format � 0: Pad1– insert single byte of padding � 1: PadN – insert 2 or more byte of padding � 5: Router Alert – indicate to the router the packets require additional processing (MLD and RSVP) � 194: Jumbo Payload – indicate payload size over 65,535 14

Hop-by-Hop Extension Header Next Header Header Extension Length Options 15 Fragmentation Fragmentation by sources only � No fragmentation by routers � End-to-end fragmentation Source � Use the Guaranteed Minimum MTU (maximum transfer unit) of 1280 octets � Perform Path MTU Discovery to identify the minimum MTU along the path 16

Fragmentation Extension Header 17 Fragmentation Process Unfragmentable part must be processed by each intermediate node and destination Fragmentable part must only processed at final destination 18

Fragmentation Packets 19 IPv6 Source Routing Source routing is optional in IPv4 Source routing in IPv6 � Leverage Routing Header 20

Routing Header So far only one type of routing header has been defined, known as type 0 The basic IP header’s destination address indicates the first hop on the desired path. The list in the routing header identifies subsequent hops along that path. The Segment left ( Addrs left ) field keeps track of the current position in the list. � Each router decrements this field by one 21 Routing Extension Header 22

2 Router C Router D 4 Destination Source 3 Router A Router E 5 1 6 4 Flow label 6 4 Flow label 6 4 Flow label Payload length Nxt:43 hops Payload length Nxt:43 hops Payload length Nxt:43 hops Src: Source Src: Source Src: Source Dst: Router A Dst: Router C Dst: Destination Nxt Len Type:0 I:4 Nxt Len Type:0 I:3 Nxt Len Type:0 I:0 0x00 0x000000 0x00 0x000000 0x00 0x000000 Address [0]: Router C Address [0]: Router A Address [0]: Router A Address [1]: Router D Address [1]: Router D Address [1]: Router C Address [2]: Router E Address [2]: Router E Address [2]: Router D Address [3]: Destination Address [3]: Destination Address [3]: Router E 23 Destination Option The destination options header contains IP options for the datagram’s destination. If the datagram includes a routing header, this header can also precede that header. In that case, its options will be processed by each intermediate hop included in the routing header’s list. 24

Destination Option Header Next Header Header Extension Length Options 25 Outline IPv6 Header IPv6 Addressing IPv6 Neighbor Discovery IPv6 Autoconfiguration 26

Address Space 2 128 = 3.4 × 10 38 addresses � 6.65 × 10 23 addresses per m 2 of earth surface If assigned at the rate of 10 6 / µ s, it would take 20 years 27 Addressing Model Addresses are assigned to interfaces � No change from IPv4 Model Interface ‘expected’ to have multiple addresses Addresses have scope � Link Local � Site Local � Global Addresses have lifetime � Valid and Preferred lifetime 28

IPv6 Internet Global Company A Router Site-local Link-local 1 Link-local 2 Router Router H A H B H 1 H 2 29 Addressing Types Unicast � Address of a single interface � Delivery to single interface Multicast � Address of a set of interfaces � Delivery to all interfaces in the set Anycast � Address of a set of interfaces � Delivery to a single interface in the set No more broadcast addresses 30

Address Format Breaks 128 bits into eight 16-bit pieces. Colons separate each piece. � FEDC:BA89:33FE:2145:D34C:3411:2311:A23B The leading zeros are not necessary, but at least one digit must be present. � 1080:0000:0001:0000:0008:0800:200C:417A => 1080:0:1:0:8:800:200C:417A 31 Address Format (cont.) For compact representation, a series of consecutive zero is abbreviated with two colons. For example: � 1080::8:800:200C:417A � the “::” abbreviation may only appear once in an address. IPv4-embedded � 0:0:0:0:0:0:13.1.68.3 or ::13.1.68.3 32

Address Prefix IPv6-address/prefix-length � prefix-length: a decimal value specifying how many of the leftmost contiguous bits of the address comprise the prefix � 1080:0:FF:0::/64 � specify the first 64 bits � no mask in IPv6 33 Prefix Type of Address 0000 0000 Reserved 0000 0001 Unassigned 0000 001 Reserved for NSAP allocation 0000 010 Reserved for IPX allocation 0000 011 Unassigned 0000 1 Unassigned 0001 Unassigned 001 Aggregatable Global Unicast Address 010 Unassigned 011 Unassigned 100 Unassigned 101 Unassigned 110 Unassigned 1110 Unassigned 1111 0 Unassigned 1111 10 Unassigned 1111 110 Unassigned 1111 1110 0 Unassigned 1111 1110 10 Link local use address (e.g. fe80::/10) 1111 1110 11 Site local use address (e.g. fec0::/10) 1111 1111 Multicast address (e.g. ff00::/8) 34

Prefix Address type Binary prefix IPv4-compatible 0000...0 (96 zero bits) global unicast 001 link-local unicast 1111 1110 10 site-local unicast 1111 1110 11 multicast 1111 1111 all other prefixes reserved (approx. 85% of total) anycast addresses allocated from unicast prefixes 35 Aggregatable Global Unicast Addresses 001 TLA Res NLA subnet interface ID public site interface topology topology identifier (45 bits) (16 bits) (64 bits) TLA (Top Level Aggregator) = 13 bits � TLA routers do not have a default route, only route with 16 bits prefix � may be assigned to providers or exchanges Res= 8 bits � Reserved for future use in expanding the size of either the TLA or NLA NLA (Next Level Aggregator)= 24 bits SLA (Site level Aggregator)= 16 bits Public topology � Collection of larger and smaller ISP Site topology � Collection of subnets within an organization’s site 36