If the community can decide what to do, then we can propose a solution.
So how it works.
NetNameResolver localHostAddress
fe80::21c:42ff:fe00:9%en5(otter-2.local),0(0)
Gah... what's that?
Well the interface is:
en5: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21c:42ff:fe00:9%en5 prefixlen 64 scopeid 0x8
inet 10.37.129.2 netmask 0xffffff00 broadcast 10.37.129.255
ether 00:1c:42:00:00:09
media: autoselect status: active
supported media: autoselect
Thus it's giving me an IPV6 address.
The chore is more complicated that one would care to see. I see Microsoft had a
hand in defining the spec.
So it first asks the gethostname for the name of the host. As an example my
macbook pro has
Otter-2.local
which is what
[otter-2:~] johnmci% hostname
Otter-2.local
That's a bonjour assigned name since if I do
[otter-2:~] johnmci% nslookup Otter-2.local
Server: 192.168.1.7
Address: 192.168.1.7#53
** server can't find Otter-2.local: NXDOMAIN
Then we are off to:
getnameinfo
which returns a chain of IPV4 and IPV6 address that Otter-2.local would
resolve to.
In this case there are six address, broken in to IPV6 and IPV4
fe80::21c:42ff:fe00:8%en4(otter-2.local),0(0)-inet6-stream-tcp
fe80::21c:42ff:fe00:9%en5(otter-2.local),0(0)-inet6-stream-tcp
fe80::21b:63ff:fe02:d2db%en1(otter-2.local),0(0)-inet6-stream-tcp
10.211.55.2(10.211.55.2),0(0)-inet4-stream-tcp
10.37.129.2(10.37.129.2),0(0)-inet4-stream-tcp
192.168.1.141(192.168.1.141),0(0)-inet4-stream-tcp
So looks kinda random, but it's not. It's defined by Microsoft & committee etc.
in
http://www.faqs.org/rfcs/rfc3484.html
The objective is to sort the list into some order. I must say you can't
actually tell from reading the docs, and things over
the past decade have changed. So I refer to some cheat sheets that *might* be
correct.
Now the macbook pro in this case uses 192.168.1.141 as the assigned tcp/ip
address from our internal DHCP server.
The 10.211.55.2 is a parallels shared network adaptor and
10.37.129.2 is the parallels host-only network adaptor.
All three interfaces show as active, and if you consider the 'ifconfig -a'
below you would be hard pressed to determine which interface is the one facing
the
company intranet.
[otter-2:~] johnmci% ifconfig -a
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet6 ::1 prefixlen 128
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:17:f2:d9:57:35
media: autoselect status: inactive
supported media: autoselect 10baseT/UTP <half-duplex> 10baseT/UTP <full-duplex> 10baseT/UTP <full-duplex,hw-loopback>
10baseT/UTP <full-duplex,flow-control> 100baseTX <half-duplex> 100baseTX <full-duplex> 100baseTX
<full-duplex,hw-loopback> 100baseTX <full-duplex,flow-control> 1000baseT <full-duplex> 1000baseT
<full-duplex,hw-loopback> 1000baseT <full-duplex,flow-control> none
fw0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 2030
lladdr 00:19:e3:ff:fe:93:92:7c
media: autoselect <full-duplex> status: inactive
supported media: autoselect <full-duplex>
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21b:63ff:fe02:d2db%en1 prefixlen 64 scopeid 0x6
inet 192.168.1.141 netmask 0xffffff00 broadcast 192.168.1.255
ether 00:1b:63:02:d2:db
media: autoselect status: active
supported media: autoselect
en4: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21c:42ff:fe00:8%en4 prefixlen 64 scopeid 0x7
inet 10.211.55.2 netmask 0xffffff00 broadcast 10.211.55.255
ether 00:1c:42:00:00:08
media: autoselect status: active
supported media: autoselect
en5: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21c:42ff:fe00:9%en5 prefixlen 64 scopeid 0x8
inet 10.37.129.2 netmask 0xffffff00 broadcast 10.37.129.255
ether 00:1c:42:00:00:09
media: autoselect status: active
supported media: autoselect
Where en0 is ethernet jack, fw0 is firewire, en1 is wireless, en4 & en5 are
virtual.
Now the bias from the committee is
precedence ::1/128 50
precedence ::/0 40
precedence 2002::/16 30
precedence ::/96 20
precedence ::ffff:0:0/96 10
scopev4 ::ffff:169.254.0.0/112 2
scopev4 ::ffff:127.0.0.0/104 2
scopev4 ::ffff:10.0.0.0/104 5
scopev4 ::ffff:172.16.0.0/108 5
scopev4 ::ffff:192.168.0.0/112 5
scopev4 ::ffff:0.0.0.0/96 14
This means of course the 10.0.0.0 address sorts before the 192.168.0.0 address.
How helpful.
So how do we know *which* is the proper address to use? Well no idea!
However let's see what the API does.
NetNameResolver class>> addressesForName: hostName
| adresses |
adresses := SocketAddressInformation
forHost: hostName
service: ''
flags: 0
addressFamily: 0
socketType: SocketAddressInformation socketTypeStream
protocol: SocketAddressInformation protocolTCP.
^adresses
Now I can make it return just IPV4 address by doing:
NetNameResolver class>> addressesForName: hostName
| adresses |
adresses := SocketAddressInformation
forHost: hostName
service: ''
flags: 0
addressFamily: SocketAddressInformation addressFamilyINET4
socketType: SocketAddressInformation socketTypeStream
protocol: SocketAddressInformation protocolTCP.
^adresses
which then NetNameResolver localHostAddress gives:
10.37.129.2(10.37.129.2),0(0)
I can also supply a service number string say SSH '22'
that give back
10.37.129.2(10.37.129.2),22(ssh)
since ssh is binding on all interfaces that's valid.
Technically the getnameinfo gives back three address but again the code below
grabs the first one which according to the rfc3484 is more likely to be the
correct answer.
addressForName: hostName
"NetNameResolver addressForName: 'impara.de' "
"NetNameResolver addressForName: 'localhost' "
"NetNameResolver addressForName: '127.0.0.1' "
| addresses |
self useOldNetwork
ifTrue: [^self oldAddressForName: hostName].
addresses := self addressesForName: hostName.
^addresses
ifEmpty: [nil]
ifNotEmpty: [addresses first socketAddress]
But grabbing the first one doesn't meet people's expectations of correctness,
however we just don't have enough information to decide *what* is correct.
Now some people say OH let's return the en0 one because that is correct? Really
how do you know?
On my computer en0 is ethernet, but since I'm using wireless then en1 is the
correct one.
Obviously I could look in the list of IPV6 address find the LOWEST en# value,
then grab the IPV4 entry. This would assume I check for the fact that the IPV6
interface has an IPV4 address and the sort order for the IPV6 is the same as
for the IPV4.
Gee that sounds ok?
Well it's not, when for example I tether my MacBook Pro to my iPhone and abuse
my privilege to move data over the cellular carrier, ah sorry you USA ATT folks,
then the interface is:
en6: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::226:8ff:fe72:5aa%en6 prefixlen 64 scopeid 0x9
inet 192.168.20.2 netmask 0xffffff00 broadcast 192.168.20.255
ether 00:26:08:72:05:aa
media: 10baseT/UTP status: active
supported media: 10baseT/UTP
which fails the test that the lowest active en# is the one we want to use.
10.37.129.2(10.37.129.2),0(0)-inet4-stream-tcp
10.211.55.2(10.211.55.2),0(0)-inet4-stream-tcp
192.168.20.2(192.168.20.2),0(0)-inet4-stream-tcp)
So the question is what would the community like to see happen. Well other than
hide under a rock and see if the problem goes away...
On 2010-03-12, at 8:41 AM, Chris Cunnington wrote:
How is NetNameResolver choosing the interface to return an IP address from?
In Cobalt this is a problem. You need the right address to connect to other
spaces. Cobalt won't let you enter it by hand, so you are at the mercy of its
guessing the correct interface.
NetNameResolver localAddressString
executed in Workspace produces the IP from my fw0 interface, which is useless.
I need it to look at ppp0.
Can it be told which interface to look at?
How does it choose?
Chris
--
===========================================================================
John M. McIntosh <[email protected]> Twitter: squeaker68882
Corporate Smalltalk Consulting Ltd. http://www.smalltalkconsulting.com
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