Lecture 11: IPv6. CSE 123: Computer Networks Alex C. Snoeren. HW 2 due FRIDAY

Transcription

1 Lectre 11: IPv6 CSE 123: Compter Networks Alex C. Snoeren HW 2 de FRIDAY

2 IP Address Problem (1991) Address space depletion In danger of rnning ot of classes A and B Why? Class C too small for most organizations (only ~250 addresses) Very few class A very carefl abot giving them ot (who has 16M hosts anyway?) Class B greatest problem CSE 123 Lectre 11: IPv6 2

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4 CIDR Classless Inter-Domain Roting (1993) Networks described by variable-length prefix and length Allows arbitrary allocation between network and host address Network Prefix Host Mask=# significant bits representing prefix e.g contained within /8:» is network and remainder (95.1.2) is host Pro: Finer grained allocation; aggregation Con: More expensive lookp: longest prefix match CSE 123 Lectre 11: IPv6 4

5 Longest Matching Prefix Forwarding table contains many prefix/length tples They need not be disjoint! E.g /20 and /23 What to do if a packet arrives for destination ? Need to find the longest prefix in the table which matches it ( /23) Not a simple table, reqires mltiple memory lookps Lots and lots of research done on this problem Lots of this work was historically done by UCSD faclty CSE 123 Lectre 11: IPv6 5

6 Rote Aggregation Combine adjacent networks in forwarding tables Helps keep forwarding table size down Organization /23 Organization /23 Organization /23 Organization Fly-By-Night-ISP Send me anything with addresses beginning /20 Internet /23 ISPs-R-Us Send me anything with addresses beginning /16 CSE 123 Lectre 11: IPv6 6

7 Most Specific Rote Bt what if address range is not contigos? Organization /23 Organization /23 Organization /23 Organization / Fly-By-Night-ISP ISPs-R-Us Send me anything with addresses beginning /20 Send me anything with addresses beginning /16 or /23 Internet CSE 123 Lectre 11: IPv6 7

8 Forwarding example Packet to arrives Path is R2 R1 H1 H2 Provider R1 H / / R / H H / / /24 H CSE 123 Lectre 11: IPv6 8

9 Forwarding example (2) Packet to Matches /23 Forwarding table at R2 Destination Next Hop loopback Defalt or 0/ /24 interface /23 interface / /24 interface3 R H / / R / H3 H H / / /24 CSE 123 Lectre 11: IPv6 9

10 Forwarding example (3) Packet to Matches /30 Longest prefix match Roting table at R1 Destination Next Hop loopback Defalt or 0/ / /24 interface1 interface /23 interface / R1 H / / R / H3 H H / / /24 CSE 123 Lectre 11: IPv6 10

11 Forwarding example (4) Packet to Direct rote Longest prefix match Roting table at H1 Destination Next Hop loopback Defalt or 0/ /24 interface /30 interface R1 H /23 H4 H / / / / R2 H / CSE 123 Lectre 11: IPv6 11

12 The space crnch Still rnning ot of IP addresses what to do? Two soltions Network Address Translation mltiple mltiple hosts on a single IP address (ftre class) Get bigger addresses -> IPv6 IPv6: 128bit addresses we won t rn ot 64bit roting prefix, 64bit host id CSE 123 Lectre 11: IPv6 12

13 IPv6 Addresses Colon-Hex notation 8 grops of for HEX digits separated by colons, e.g.» FEDC:0000:0000:0065:4321:0000:DEAD:BEEF Can drop leading zeros:» FEDC:0000:0000:65:4321:0000:DEAD:BEEF Can even skip first seqence of all zeros w/ ::» FEDC::65:4321:0000:DEAD:BEEF Every IPv4 address is a IPv6 address:» E.g., ::FFFF: (prepended w/zeros and FFFF) Network names expressed as prefix/length:» FEDC::65:43/50 CSE 123 Lectre 11: IPv6 13

14 Address Types Each interface has mltiple different addresses Link local, prefixed with FE80::/10 ( )» Used only for commnication between adjacent IPv6 devices» Packets are NOT forwarded by roters» Atomatically assigned pon boot Uniqe local, prefixed with FC00::/7 ( )» Used only internal to one network» Not rotable on the global Internet Global» Like an IPv4 address CSE 123 Lectre 11: IPv6 14

15 IPv6 vs IPv4 header Ver. Traffic Class Flow Label Ver. Hdr Len Type of Service Total Length Payload Length Next Header Hop Limit Identification Flg Fragment Offset Time to Live Protocol Header Checksm Sorce Address Sorce Address Destination Address Options... Gray bits are niqe to each header Destination Address CSE 123 Lectre 11: IPv6 Changes Eliminate fragmentation-related fields Eliminate header checksm Added flow label Qadrple size of addresses IPv6 header (40 bytes) vs IPv4 (20 bytes) 15

16 Extension Headers Effectively a linked list of headers The next header field is the pointer Two different types Destination, intended for the IP end point. E.g.,» 44: Fragmentation Header (it s baaack!)» 43: Roting header (dictates how to rote the packet) Hop-by-hop, processed by each node on the path CSE 123 Lectre 11: IPv6 16

17 IPv6 Transition is slow Need to spport both protocols at the same time Complicated if a destination has both a IPv4 and IPv6 address which to se? Less need in developed world -> slower adoption That said All major operating systems now spport IPv6 All major roter vendors US Mobile carriers (e.g., Tmobile, Verizon, etc) Offered as option by many US ISPs In yor lifetime it is likely that IPv6-based addressing will start to dominate CSE 123 Lectre 11: IPv6 17

18 Smmary Yo can t rote efficiently on flat address spaces Yo d need a table the size of all hosts on the Internet Yo d need to send pdates abot that table to everyone Network-layer addressing is done hierarchically Roting prefix + host sffix Originally, this split was done statically (class-based addressing) Now it is done dynamically (CIDR) Reqires more complex forwarding table lookp Allows contigos chnks of address space to be aggregated (for the prposes of roting) into fewer prefixes CSE 123 Lectre 11: IPv6 18

19 For Next Time Finish p Project 1; de next MONDAY! Last discssion before deadline TOMORROW! Read 3.2.6, 9.3.1, Sidebar p.335 for next Lectre CSE 123 Lectre 11: IPv6 19