Marcel Holtmann <marcel@xxxxxxxxxxxx> writes:
> As I said, there is only one address. And the is your IP address. The
> gateway is made up by the card.
Really? How can it do that? Just stealing addresses which it knows
will be in use by other clients? That's not nice :-(
Anyway, as I said, this is done regardless of raw IP mode or not. It's
not just DHCP. You get the gateway address and netmask using the QMI
command as well, although you don't really need them as you correctly
point out.
Sample output when running in raw IP mode (0x1e is address, 0x20 is
gateway, 0x21 is netmask, 0x15 and 0x16 are DNS servers):
<= QMUX Header:
<= len: 0x008e
<= sender: 0x80
<= svc: 0x01
<= cid: 0x03
<= QMI Header:
<= Flags: 0x02
<= TXN: 0x0006
<= Cmd: 0x002d
<= Size: 0x0082
<= [0x02] ( 4) 00 00 00 00 SUCCESS - QMI_ERR_NONE
<= [0x10] ( 8) 70 72 6f 66 69 6c 65 31 profile1
<= [0x11] ( 1) 00 .
<= [0x14] (13) 70 69 6c 6f 74 2e 74 65 6c 65 6e 6f 72 pilot.telenor
<= [0x15] ( 4) 04 70 d5 c1 193.213.112.4
<= [0x16] ( 4) c6 0f 43 82 130.67.15.198
<= [0x17] (33) 04 f6 02 00 00 3e 03 00 00 01 00 00 00 01 00 00 00 02 dc 05 00 00 04 07 03 00 00 00 00 01 00 00 00 .....>...........................
<= [0x1d] ( 1) 00 .
<= [0x1e] ( 4) 1d 31 90 0a 10.144.49.29
<= [0x1f] ( 2) 00 01 ..
<= [0x20] ( 4) 1e 31 90 0a 10.144.49.30
<= [0x21] ( 4) fc ff ff ff 255.255.255.252
<= [0x22] ( 1) 00 .
<= [0x23] ( 1) 00 .
<= [0x24] ( 1) 00 .
This results in a virtual ethernet interface like this, faking ethernet:
bjorn@nemi:~$ ifconfig wwan1
wwan1 Link encap:Ethernet HWaddr 00:a0:c6:00:00:00
inet addr:10.144.49.29 Bcast:10.144.49.31 Mask:255.255.255.252
inet6 addr: fe80::2a0:c6ff:fe00:0/64 Scope:Link
UP BROADCAST RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:2 errors:0 dropped:0 overruns:0 frame:0
TX packets:15 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:612 (612.0 B) TX bytes:2244 (2.1 KiB)
Note that the NOARP flag means that there is no ARP, and that implies
that the netmask and gateway have no real meaning either. Any packet
routed out this interface will be just blindly forwarded without any L2
address lookup. So the netmask may mean something in the routing table,
but assuming that there is a default route out here as well, then it's
really pointless.
And the netmask and default route can be changed to anything I like,
even this:
nemi:/home/bjorn# ifconfig wwan1 10.144.49.29 netmask 255.255.255.255 broadcast 10.144.49.29
nemi:/home/bjorn# ip route add default dev wwan1
which works just fine, as expected:
bjorn@nemi:~$ ip route get 193.0.0.193
193.0.0.193 dev wwan1 src 10.144.49.29
cache ipid 0xf49e
bjorn@nemi:~$ ping -c3 193.0.0.193
PING 193.0.0.193 (193.0.0.193) 56(84) bytes of data.
64 bytes from 193.0.0.193: icmp_req=1 ttl=53 time=85.7 ms
64 bytes from 193.0.0.193: icmp_req=2 ttl=53 time=92.2 ms
64 bytes from 193.0.0.193: icmp_req=3 ttl=53 time=89.0 ms
--- 193.0.0.193 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 85.798/89.051/92.276/2.655 ms
But there isn't really anything gained by that. And we can do the same
thing with the device in "ethernet" mode. Hmm, maybe we should set the
IFF_NOARP flag by default? Anyway, testing is easy: ifconfig wwan1 -arp
works just as expected: The device doesn't actually care about the MAC
addresses.
But this probably goes for any such modem. I just tried the same with
the builtin Ericsson modem in this laptop. After connecting and
configuring it with DHCP:
nemi:/home/bjorn# ifconfig wwan0
wwan0 Link encap:Ethernet HWaddr 02:80:37:ec:02:00
inet addr:77.17.136.228 Bcast:77.17.136.231 Mask:255.255.255.248
inet6 addr: fe80::80:37ff:feec:200/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:108 errors:0 dropped:0 overruns:0 frame:0
TX packets:123 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:10332 (10.0 KiB) TX bytes:18114 (17.6 KiB)
Turn off ARP and change to /32 mask:
nemi:/home/bjorn# ifconfig wwan0 -arp
nemi:/home/bjorn# ifconfig wwan0 77.17.136.228 netmask 255.255.255.255 broadcast 77.17.136.228
nemi:/home/bjorn# ip route add default dev wwan0
nemi:/home/bjorn# ifconfig wwan0
wwan0 Link encap:Ethernet HWaddr 02:80:37:ec:02:00
inet addr:77.17.136.228 Bcast:77.17.136.228 Mask:255.255.255.255
inet6 addr: fe80::80:37ff:feec:200/64 Scope:Link
UP BROADCAST RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:121 errors:0 dropped:0 overruns:0 frame:0
TX packets:139 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:11611 (11.3 KiB) TX bytes:19806 (19.3 KiB)
bjorn@nemi:~$ ip route get 193.0.0.193
193.0.0.193 dev wwan0 src 77.17.136.228
cache ipid 0xf49e
bjorn@nemi:~$ ping -c3 193.0.0.193
PING 193.0.0.193 (193.0.0.193) 56(84) bytes of data.
64 bytes from 193.0.0.193: icmp_req=1 ttl=54 time=81.4 ms
64 bytes from 193.0.0.193: icmp_req=2 ttl=54 time=76.7 ms
64 bytes from 193.0.0.193: icmp_req=3 ttl=54 time=79.5 ms
--- 193.0.0.193 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 76.762/79.273/81.460/1.958 ms
So maybe all such devices should really have ARP turned off and have
NetworkManager automagically reconfigure to /32 masks with no gateway
address?
Or whatever. It still doesn't make any argument for supporting the raw
IP mode of the Qualcomm modems. As shown above, the addressing issue
can just as well be solved using the ethernet mode and not relying on
any driver changes. And that goes for the Ericsson modem as well,
despite that being a completely different implementation.
Bjørn
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