【正文】 te optimization is a fundamental part of the protocol. ?Mobile IPv6 route optimization can operate securely even without prearranged security associations. 72 清華大學 研究生課程 上一頁 下一頁 Comparison with Mobile IPv4 ?Support is also integrated into Mobile IPv6 for allowing route optimization to coexist efficiently with routers that perform ingress filtering. ?Most packets sent to a mobile node while away from home in Mobile IPv6 are sent using an IPv6 routing header. ?Mobile IPv6 is decoupled from any particular link layer, as it uses IPv6 Neighbor Discovery instead of ARP. 73 清華大學 研究生課程 ICMP and ND 74 清華大學 研究生課程 上一頁 下一頁 ICMP Error Messages mon format As much of the invoking packet as will fit without the ICMP packet exceeding 1280 octets (code and parameter are typespecific) Type Code Checksum Parameter 75 清華大學 研究生課程 上一頁 下一頁 ICMP Error Message Types ?destination unreachable – no route – administratively prohibited – address unreachable – port unreachable ?packet too big ?time exceeded ?parameter problem – erroneous header field – unrecognized next header type – unrecognized option 76 清華大學 研究生課程 上一頁 下一頁 ICMP Informational Messages ? Echo request reply (same as IPv4) ? Multicast listener discovery messages: query, report, done (like IGMP for IPv4): Type Code Checksum Maximum Response Delay Reserved Multicast Address 77 清華大學 研究生課程 上一頁 下一頁 Neighbor Discovery ? ICMP message types: – router solicitation – router advertisement – neighbor solicitation – neighbor advertisement – redirect ? Functions performed: – router discovery – prefix discovery – autoconfiguration of address other parameters – duplicate address detection (DAD) – neighbor unreachability detection (NUD) – Linklayer address resolution – firsthop redirect 78 清華大學 研究生課程 上一頁 下一頁 Router Advertisements ? Periodically multicast by router to allnodes multicast address (link scope) ? Contents: – “ I am a router” (implied) list of: – lifetime as default (1 sec – 18 hr) 187。 prefix – “ get addresses from DHCP” flag 187。 prefix length – “ get other stuff from DHCP” flag 187。 valid lifetime – router’ s linklayer address 187。 preferred lifetime – link MTU 187。 onlink flag – suggested hop limit 187。 autoconfig OK flag ? Not sent frequently enough for unreachability detection 79 清華大學 研究生課程 上一頁 下一頁 Other Neighbor Discovery Messages ? Router solicitations – sent only at host startup, to solicit immediate router advert. – sent to allrouters multicast address (link scope) ? Neighbor solicitations – for address resolution: sent to “ solicited node” multicast addr. – for unreachability detection: sent to neighbor’ s unicast addr. ? Neighbor advertisements – for address resolution: sent to unicast address of solicitor – for linklayer address change: sent to allnodes multicast addr. – includes router/host flag 80 清華大學 研究生課程 上一頁 下一頁 Serverless Autoconfiguration ? Hosts can construct their own addresses: – sub prefix(es) learned from periodic multicast advertisements from neighboring router(s) – interface IDs generated locally ? Other IPlayer parameters also learned from router adverts (., router addresses, remended hop limit, etc.) ? Higherlayer info (., DNS server and NTP server addresses) discovered by multicast / anycastbased servicelocation protocol ? DHCP also available for those who want more control 81 清華大學 研究生課程 上一頁 下一頁 AutoReconfiguration (“ Renumbering” ) ? New address prefixes can be introduced, and old ones withdrawn – we assume some overlap period between old and new, ., no “ flash cutover” – hosts learn prefix lifetimes and preference order from router advertisements – old TCP connections can survive until end of overlap。 new TCP connections can survive beyond overlap ? Router renumbering protocol, to allow domaininterior routers to learn of prefix introduction / withdrawal ? New DNS structure to facilitate prefix changes 82 清華大學 研究生課程 上一頁 下一頁 Minimum MTU ? Definitions: – link MTU a link’ s maximum transmission unit, ., the max IP packet size that can be transmitted over the link – path MTU the minimum MTU of all the links in a path between a source and a destination ? Minimum link MTU for IPv6 is 1280 octets (versus 68 octets for IPv4) ? On links with MTU 1280, linkspecific fragmentation and reassembly must be used 83 清華大學 研究生課程 上一頁 下一頁 Path MTU Discovery ? Implementations are expected to perform path MTU discovery to send packets bigger than 1280 octets: – for each dest., start by assuming MTU of firsthop link – if a packet reaches a link in which it cannot fit, will invoke ICMP “ packet too big” message to source, reporting the link’ s MTU。 MTU is cached by source for specific destination – occasionally discard cached MTU to detect possible increase ? Minimal implementation can omit path MTU discovery as long as all packets kept ≤ 1280 octets – ., in a boot ROM implementation 84 清華大學 研究生課程 上一頁 下一頁 ND Autoconfiguration, Prefix Parameter Discovery ?Router solicitation are sent by booting nodes to request RAs for configuring the interfaces. 1. RS: ICMP Type = 133 Src = :: Dst = AllRouters multicast Address query= please send RA 2. RA 2. RA 1. RS 2. RA: ICMP Type = 134 Src = Router Linklocal Address Dst = Allnodes multicast address Data= options, prefix, lifetime, autoconfig flag 85 清華大學 研究生課程 上一頁 下一頁 ND Address Resolution Neighbor Unreachability Detection ICMP type = 135 (NS) Src = A