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- File wiki/handover.md — part of check-in [759f8507fc] at 2019-03-09 22:55:59 on branch trunk — Use html parser to convert wiki files to md files (user: bernd size: 2265)
0000: 23 20 48 61 6e 64 6f 76 65 72 20 23 0a 0a 4d 6f # Handover #..Mo 0010: 62 69 6c 65 20 63 6f 6d 6d 75 6e 69 63 61 74 69 bile communicati 0020: 6f 6e 20 69 73 20 6f 6e 65 20 6f 66 20 74 68 65 on is one of the 0030: 20 74 68 69 6e 67 73 20 74 68 61 74 20 64 69 64 things that did 0040: 6e 27 74 20 63 6f 6d 65 20 74 6f 20 74 68 65 20 n't come to the 0050: 6d 69 6e 64 20 6f 66 20 74 68 65 0a 70 65 6f 70 mind of the.peop 0060: 6c 65 20 77 68 6f 20 69 6e 76 65 6e 74 65 64 20 le who invented 0070: 74 68 65 20 49 6e 74 65 72 6e 65 74 20 33 30 20 the Internet 30 0080: 79 65 61 72 73 20 61 67 6f 2e 20 54 68 65 72 65 years ago. There 0090: 20 77 61 73 20 6f 76 65 72 2d 74 68 65 2d 61 69 was over-the-ai 00a0: 72 0a 63 6f 6d 6d 75 6e 69 63 61 74 69 6f 6e 20 r.communication 00b0: 65 76 65 6e 20 62 65 66 6f 72 65 2c 20 65 73 70 even before, esp 00c0: 65 63 69 61 6c 6c 79 20 74 68 65 20 41 4c 4f 48 ecially the ALOH 00d0: 41 6e 65 74 20 73 68 6f 75 6c 64 20 62 65 20 6d Anet should be m 00e0: 65 6e 74 69 6f 6e 65 64 2c 20 62 75 74 0a 74 68 entioned, but.th 00f0: 65 20 63 6f 6d 70 75 74 65 72 73 20 77 65 72 65 e computers were 0100: 20 74 6f 6f 20 6c 61 72 67 65 20 74 6f 20 62 65 too large to be 0110: 20 63 61 72 72 69 65 64 20 61 72 6f 75 6e 64 2e carried around. 0120: 20 41 6e 64 20 61 6c 6c 20 73 74 61 74 69 6f 6e And all station 0130: 73 20 77 65 72 65 0a 77 69 74 68 69 6e 20 72 65 s were.within re 0140: 61 63 68 20 6f 66 20 65 61 63 68 20 6f 74 68 65 ach of each othe 0150: 72 73 20 28 62 79 20 75 73 69 6e 67 20 70 72 65 rs (by using pre 0160: 74 74 79 20 73 74 72 6f 6e 67 20 73 69 67 6e 61 tty strong signa 0170: 6c 73 20 e2 80 94 20 74 68 65 20 48 61 77 61 69 ls — the Hawai 0180: 69 0a 69 73 6c 61 6e 64 73 20 61 72 65 20 6e 6f i.islands are no 0190: 74 20 74 68 61 74 20 73 6d 61 6c 6c 29 2e 20 48 t that small). H 01a0: 61 6e 64 6f 76 65 72 20 6d 65 61 6e 73 20 74 68 andover means th 01b0: 61 74 20 61 6e 20 65 6e 64 20 6e 6f 64 65 20 72 at an end node r 01c0: 65 67 75 6c 61 72 6c 79 20 63 68 61 6e 67 65 73 egularly changes 01d0: 0a 74 68 65 20 73 74 61 74 69 6f 6e 20 69 74 27 .the station it' 01e0: 73 20 63 6f 6e 6e 65 63 74 65 64 20 74 6f 2e 20 s connected to. 01f0: 57 69 74 68 20 61 20 73 77 69 74 63 68 69 6e 67 With a switching 0200: 20 73 79 73 74 65 6d 20 6c 69 6b 65 20 6e 65 74 system like net 0210: 32 6f 2c 20 74 68 69 73 20 6d 65 61 6e 73 2c 0a 2o, this means,. 0220: 74 68 65 20 61 64 64 72 65 73 73 20 63 68 61 6e the address chan 0230: 67 65 73 2e 20 54 68 65 20 63 6f 6d 6d 75 6e 69 ges. The communi 0240: 63 61 74 69 6f 6e 20 68 6f 77 65 76 65 72 20 73 cation however s 0250: 68 6f 75 6c 64 20 63 6f 6e 74 69 6e 75 65 20 65 hould continue e 0260: 76 65 6e 20 77 68 65 6e 20 73 75 63 68 0a 61 6e ven when such.an 0270: 20 61 64 64 72 65 73 73 20 63 68 61 6e 67 65 20 address change 0280: 68 61 70 70 65 6e 73 20 66 72 65 71 75 65 6e 74 happens frequent 0290: 6c 79 2e 20 41 6e 64 20 69 74 20 73 68 6f 75 6c ly. And it shoul 02a0: 64 20 77 6f 72 6b 20 65 76 65 6e 20 77 68 65 6e d work even when 02b0: 20 62 6f 74 68 20 6e 6f 64 65 73 0a 68 6f 70 20 both nodes.hop 02c0: 66 72 6f 6d 20 73 74 61 74 69 6f 6e 20 74 6f 20 from station to 02d0: 73 74 61 74 69 6f 6e 2e 20 4e 6f 20 63 6f 6d 70 station. No comp 02e0: 6c 69 63 61 74 65 64 20 72 65 6e 65 67 6f 74 69 licated renegoti 02f0: 61 74 69 6f 6e 20 73 68 6f 75 6c 64 20 68 61 70 ation should hap 0300: 70 65 6e 2c 20 61 6e 64 0a 6e 6f 20 72 6f 75 74 pen, and.no rout 0310: 69 6e 67 20 73 65 72 76 65 72 20 73 68 6f 75 6c ing server shoul 0320: 64 20 62 65 20 71 75 65 72 69 65 64 20 69 66 20 d be queried if 0330: 73 75 63 68 20 61 20 74 68 69 6e 67 20 68 61 70 such a thing hap 0340: 70 65 6e 73 20 6f 6e 20 61 6e 20 6f 70 65 6e 0a pens on an open. 0350: 63 6f 6e 6e 65 63 74 69 6f 6e 2e 20 54 68 65 20 connection. The 0360: 69 64 65 61 20 74 6f 20 61 63 68 69 65 76 65 20 idea to achieve 0370: 74 68 69 73 20 69 73 20 66 61 69 72 6c 79 20 74 this is fairly t 0380: 72 69 76 69 61 6c 3a 0a 0a 2a 20 6e 65 74 32 6f rivial:..* net2o 0390: 20 61 64 64 72 65 73 73 65 73 20 61 72 65 20 75 addresses are u 03a0: 6e 69 71 75 65 20 63 6f 6e 6e 65 63 74 69 6f 6e nique connection 03b0: 73 0a 2a 20 41 6e 79 20 72 65 70 6c 79 20 74 6f s.* Any reply to 03c0: 20 61 6e 20 6f 70 65 6e 20 63 6f 6e 6e 65 63 74 an open connect 03d0: 69 6f 6e 20 69 73 20 73 65 6e 74 20 74 6f 20 74 ion is sent to t 03e0: 68 65 20 6c 61 73 74 20 72 65 63 65 69 76 65 64 he last received 03f0: 20 72 65 74 75 72 6e 20 61 64 64 72 65 73 73 0a return address. 0400: 2a 20 57 68 65 6e 20 61 6e 20 65 6e 64 20 6e 6f * When an end no 0410: 64 65 20 63 68 61 6e 67 65 73 20 74 68 65 20 73 de changes the s 0420: 74 61 74 69 6f 6e 2c 20 69 74 20 77 69 6c 6c 20 tation, it will 0430: 70 69 6e 67 20 61 6c 6c 20 6f 70 65 6e 20 63 6f ping all open co 0440: 6e 6e 65 63 74 69 6f 6e 73 20 61 6e 64 0a 20 20 nnections and. 0450: 74 68 75 73 20 69 6e 66 6f 72 6d 20 74 68 65 20 thus inform the 0460: 70 65 65 72 73 20 61 62 6f 75 74 20 74 68 61 74 peers about that 0470: 20 63 68 61 6e 67 65 0a 2a 20 43 68 61 6e 67 69 change.* Changi 0480: 6e 67 20 73 74 61 74 69 6f 6e 73 20 6e 65 65 64 ng stations need 0490: 20 61 20 74 69 6d 65 20 6f 76 65 72 6c 61 70 2c a time overlap, 04a0: 20 64 75 72 69 6e 67 20 77 68 69 63 68 20 74 68 during which th 04b0: 65 20 65 6e 64 20 6e 6f 64 65 20 69 73 0a 20 20 e end node is. 04c0: 72 65 61 63 68 61 62 6c 65 20 74 68 72 6f 75 67 reachable throug 04d0: 68 20 62 6f 74 68 20 74 68 65 20 6f 6c 64 20 61 h both the old a 04e0: 6e 64 20 74 68 65 20 6e 65 77 20 61 64 64 72 65 nd the new addre 04f0: 73 73 2e 0a 0a 54 68 69 73 20 6f 76 65 72 6c 61 ss...This overla 0500: 70 20 74 69 6d 65 20 69 73 20 6e 65 63 65 73 73 p time is necess 0510: 61 72 79 20 69 66 20 74 77 6f 20 63 6f 6e 6e 65 ary if two conne 0520: 63 74 65 64 20 6e 6f 64 65 73 20 63 68 61 6e 67 cted nodes chang 0530: 65 20 73 74 61 74 69 6f 6e 20 61 74 20 74 68 65 e station at the 0540: 0a 73 61 6d 65 20 74 69 6d 65 2e 20 41 73 20 74 .same time. As t 0550: 68 65 20 63 6f 6d 6d 75 6e 69 63 61 74 69 6f 6e he communication 0560: 20 69 74 73 65 6c 66 20 69 73 20 70 72 6f 74 65 itself is prote 0570: 63 74 65 64 20 62 79 20 65 6e 63 72 79 70 74 69 cted by encrypti 0580: 6f 6e 20 66 72 6f 6d 0a 69 6e 74 72 75 64 65 72 on from.intruder 0590: 73 2c 20 74 68 69 73 20 69 73 20 73 61 76 65 20 s, this is save 05a0: 65 76 65 6e 20 77 69 74 68 6f 75 74 20 70 72 65 even without pre 05b0: 73 65 6e 74 69 6e 67 20 73 6f 6d 65 20 74 69 63 senting some tic 05c0: 6b 65 74 20 66 6f 72 20 74 68 65 0a 68 61 6e 64 ket for the.hand 05d0: 6f 76 65 72 2e 20 54 68 65 20 6f 76 65 72 6c 61 over. The overla 05e0: 70 20 74 69 6d 65 20 63 61 6e 20 62 65 20 61 6c p time can be al 05f0: 73 6f 20 61 63 68 69 65 76 65 64 20 62 79 20 74 so achieved by t 0600: 65 6d 70 6f 72 61 72 69 6c 79 20 66 6f 72 77 61 emporarily forwa 0610: 72 64 69 6e 67 0a 70 61 63 6b 65 74 73 20 66 72 rding.packets fr 0620: 6f 6d 20 74 68 65 20 6f 6c 64 20 64 65 73 74 69 om the old desti 0630: 6e 61 74 69 6f 6e 20 e2 80 94 20 74 68 69 73 20 nation — this 0640: 69 73 20 74 68 65 20 70 72 65 66 65 72 72 65 64 is the preferred 0650: 20 77 61 79 20 74 6f 20 6d 69 67 72 61 74 65 0a way to migrate. 0660: 76 69 72 74 75 61 6c 20 6d 61 63 68 69 6e 65 73 virtual machines 0670: 20 74 6f 20 6e 65 77 20 68 6f 73 74 73 20 e2 80 to new hosts †0680: 94 20 74 68 65 20 6f 6c 64 20 68 6f 73 74 20 74 ” the old host t 0690: 65 6d 70 6f 72 61 72 69 6c 79 20 66 6f 72 77 61 emporarily forwa 06a0: 72 64 73 20 61 6c 6c 20 72 65 63 65 69 76 65 64 rds all received 06b0: 0a 70 61 63 6b 65 74 73 20 74 6f 20 74 68 65 20 .packets to the 06c0: 6e 65 77 20 68 6f 73 74 2c 20 61 6e 64 20 61 66 new host, and af 06d0: 74 65 72 20 61 20 73 68 6f 72 74 20 74 69 6d 65 ter a short time 06e0: 20 63 61 6e 20 62 65 20 75 73 65 64 20 66 6f 72 can be used for 06f0: 20 73 6f 6d 65 74 68 69 6e 67 0a 65 6c 73 65 2e something.else. 0700: 20 46 72 6f 6d 20 61 20 66 69 72 65 77 61 6c 6c From a firewall 0710: 20 70 6f 69 6e 74 20 6f 66 20 76 69 65 77 2c 20 point of view, 0720: 74 68 69 73 20 61 70 70 72 6f 61 63 68 20 6c 6f this approach lo 0730: 6f 6b 73 20 73 63 61 72 79 2e 20 57 68 65 6e 20 oks scary. When 0740: 61 20 73 79 73 74 65 6d 0a 6f 70 65 6e 73 20 61 a system.opens a 0750: 20 63 6f 6e 6e 65 63 74 69 6f 6e 20 28 77 68 69 connection (whi 0760: 63 68 20 63 6f 6e 73 69 73 74 73 20 6f 66 20 73 ch consists of s 0770: 6f 6d 65 20 61 64 64 72 65 73 73 20 72 61 6e 67 ome address rang 0780: 65 73 29 2c 20 74 68 69 73 20 61 64 64 72 65 73 es), this addres 0790: 73 20 72 61 6e 67 65 0a 69 73 20 6f 70 65 6e 20 s range.is open 07a0: 74 6f 20 61 6e 79 62 6f 64 79 2e 20 41 6e 64 20 to anybody. And 07b0: 77 6f 72 73 65 20 79 65 74 2c 20 73 69 6e 63 65 worse yet, since 07c0: 20 74 68 65 20 61 64 64 72 65 73 73 20 69 73 20 the address is 07d0: 6e 6f 74 20 65 6e 63 72 79 70 74 65 64 2c 0a 65 not encrypted,.e 07e0: 76 65 72 79 62 6f 64 79 20 63 61 6e 20 6b 6e 6f verybody can kno 07f0: 77 20 77 68 69 63 68 20 61 72 65 20 6c 65 67 69 w which are legi 0800: 74 69 6d 61 74 65 20 61 64 64 72 65 73 73 65 73 timate addresses 0810: 2c 20 62 79 20 6f 62 73 65 72 76 69 6e 67 20 74 , by observing t 0820: 68 65 20 74 72 61 66 66 69 63 0a 66 6f 72 20 61 he traffic.for a 0830: 20 77 68 69 6c 65 2e 20 54 68 65 20 62 6c 6f 63 while. The bloc 0840: 6b 69 6e 67 20 6f 66 20 69 6e 74 72 75 64 65 72 king of intruder 0850: 73 20 68 61 70 70 65 6e 73 20 73 6f 6c 65 6c 79 s happens solely 0860: 20 74 68 72 6f 75 67 68 20 65 6e 63 72 79 70 74 through encrypt 0870: 69 6f 6e 2c 20 61 6e 64 0a 74 68 61 74 20 65 6e ion, and.that en 0880: 63 72 79 70 74 69 6f 6e 20 69 73 20 75 6e 6b 6e cryption is unkn 0890: 6f 77 6e 20 74 6f 20 74 68 65 20 66 69 72 65 77 own to the firew 08a0: 61 6c 6c 20 28 77 68 69 63 68 20 69 73 20 74 68 all (which is th 08b0: 65 20 77 68 6f 6c 65 20 70 6f 69 6e 74 20 6f 66 e whole point of 08c0: 0a 65 6e 63 72 79 70 74 69 6f 6e 2c 20 61 66 74 .encryption, aft 08d0: 65 72 20 61 6c 6c 29 2e 0a er all)..