The source address selection mechanism in IPv4 is to my understanding: the first address on the interface associated with the route to the remote host
The source address selection mechanism in IPv6 is to my understanding: for each of the global addresses on a system, turn it into an integer and subtract it from the destination address. The difference closest to zero decides what address will be selected because it is 'closest'. Personally I'd be happy if IPv6 mimicked IPv4 in this regard. Other OS's permit configurable address selection criteria in the kernel, but I'll be the first to suggest this is not the OpenBSD way. The default should be good enough and .. this is not good enough for me in every scenario I've encountered it. Naddy may pipe up as well, he's quite familiar with this scenario. Thanks, Penned by Stuart Henderson on 20130219 19:11.10, we have: | Someone trying to replace some latvian boxes with bgpd/npppd mentioned | a problem with v6 on carp interfaces in 'backup' state where their | address was used as source address, despite there being an address | on the carpdev which was up. | | I don't have a proper v6 carp setup handy to test but got a test | machine into a state with 'ifconfig carp0 down' (which seems should be | a close enough equivalent to 'carp backup' for tests) which did | indeed consider the 'down' carp interface as a source address. | | It can be bodged around with pltime 0 of course, but from looking at | in6_selectsrc() I don't see why it wouldn't just pick the address | from the interface associated with the route i.e. the one on em0.. | but then I must be missing something as I don't see where pltime 0 | is handled either... does anyone have clues? | | # ifconfig em0 | em0: flags=48b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST,INET6_NOPRIVACY> mtu 1500 | lladdr f0:de:f1:f9:a7:52 | priority: 0 | groups: egress | media: Ethernet autoselect (1000baseT full-duplex) | status: active | inet6 fe80::f2de:f1ff:fef9:a752%em0 prefixlen 64 scopeid 0x1 | inet6 2001:8b0:648e:cc01:f2de:f1ff:fef9:a752 prefixlen 64 autoconf pltime 604697 vltime 2591897 | inet 85.158.44.149 netmask 0xfffffff0 broadcast 85.158.44.159 | # ifconfig carp0 | carp0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500 | lladdr 00:00:5e:00:01:01 | priority: 0 | carp: INIT carpdev em0 vhid 1 advbase 1 advskew 0 | groups: carp | status: invalid | inet6 fe80::200:5eff:fe00:101%carp0 prefixlen 64 scopeid 0xa | inet6 2001:8b0:648e:cc01:200:5eff:fe00:101 prefixlen 64 detached autoconf pltime 604690 vltime 2591890 | inet6 2001:8b0:648e:cc01:5c46:9730:9899:1008 prefixlen 64 detached autoconf autoconfprivacy pltime 81660 vltime 600216 | inet6 2001:8b0:648e:cc01::ca1f prefixlen 64 | # $ route -n get -inet6 2001:8b0:648e:cc01:20d:b9ff:fe04:a330 | route to: 2001:8b0:648e:cc01:20d:b9ff:fe04:a330 | destination: 2001:8b0:648e:cc01:: | mask: ffff:ffff:ffff:ffff:: | interface: em0 | if address: fe80::f2de:f1ff:fef9:a752%em0 | priority: 4 (connected) | flags: <UP,DONE,CLONING> | use mtu expire | 0 0 0 | # ping6 jodrell | PING6(56=40+8+8 bytes) 2001:8b0:648e:cc01::ca1f --> 2001:8b0:648e:cc01:20d:b9ff:fe04:a330 | ^C | --- jodrell.spacehopper.org ping6 statistics --- | 3 packets transmitted, 0 packets received, 100.0% packet loss | | | # netstat -rnfinet6|grep -e 2001:8b0:648e:cc01 -e carp0 | 2001:8b0:648e:cc01::/64 link#1 UC 7 0 - 4 em0 | 2001:8b0:648e:cc01::1 00:0d:b9:17:0c:c4 UHLc 0 5 - 4 em0 | 2001:8b0:648e:cc01::ca1f link#1 UHLc 1 0 - 4 em0 | 2001:8b0:648e:cc01:200:5eff:fe00:101 00:00:5e:00:01:01 UHL 0 0 - 4 lo0 | 2001:8b0:648e:cc01:20d:93ff:fe63:da5a 00:0d:93:63:da:5a UHLc 1 8 - 4 em0 | 2001:8b0:648e:cc01:20d:b9ff:fe04:a330 00:0d:b9:17:0c:c4 UHLc 0 3 - 4 em0 | 2001:8b0:648e:cc01:5c46:9730:9899:1008 00:00:5e:00:01:01 UHL 0 0 - 4 lo0 | 2001:8b0:648e:cc01:f2de:f1ff:fef9:a752 f0:de:f1:f9:a7:52 UHLc 0 0 - 4 lo0 | fe80::%carp0/64 link#10 UC 12 0 - 4 carp0 | fe80::200:5eff:fe00:101%carp0 00:00:5e:00:01:01 UHL 0 0 - 4 lo0 | fe80::20d:93ff:fe63:da5a%carp0 00:0d:93:63:da:5a UHLc 0 2 - 4 carp0 | fe80::20d:b9ff:fe17:cc4%carp0 00:0d:b9:17:0c:c4 UHLc 0 0 - 4 carp0 | ff01::%carp0/32 link#10 UC 0 0 - 4 carp0 | ff02::%carp0/32 link#10 UC 2 0 - 4 carp0 | ff02::1:ff04:a330%carp0 link#10 UHLc 0 0 - 4 carp0 | ff02::1:ff63:da5a%carp0 link#10 UHLc 0 0 - 4 carp0 -- Todd Fries .. t...@fries.net ____________________________________________ | \ 1.636.410.0632 (voice) | Free Daemon Consulting, LLC \ 1.405.227.9094 (voice) | http://FreeDaemonConsulting.com \ 1.866.792.3418 (FAX) | PO Box 16169, Oklahoma City, OK 73113 \ sip:freedae...@ekiga.net | "..in support of free software solutions." \ sip:4052279...@ekiga.net \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ 37E7 D3EB 74D0 8D66 A68D B866 0326 204E 3F42 004A http://todd.fries.net/pgp.txt
