udhcpc in 1.10.3 doesnt like my WLAN card
Denys Vlasenko
vda.linux at googlemail.com
Thu Jun 19 18:58:19 UTC 2008
On Thursday 19 June 2008 14:43, Cristian Ionescu-Idbohrn wrote:
> The problem seems to be that your wlan-card does not see/catch the
> dhcp-offer.
Cristian, this is not true. In tcpdump I see
This is the packet "from us":
14:20:27.629001 IP (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto:
UDP (17), length: 576) 0.0.0.0.68 > 255.255.255.255.67: [udp sum ok]
BOOTP/DHCP, Request from 50:00:00:00:26:00, length 548, xid 0x51d537f3,
Flags [ none ] (0x0000)
Client-Ethernet-Address 50:00:00:00:26:00
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: Discover
Client-ID Option 61, length 7: ether 50:00:00:00:26:00
Vendor-Class Option 60, length 12: "udhcp 1.10.3"
MSZ Option 57, length 2: 576
Parameter-Request Option 55, length 7:
Subnet-Mask, Default-Gateway, Domain-Name-Server, Hostname
Domain-Name, BR, NTP
and this is the reply:
14:20:28.633227 IP (tos 0x10, ttl 64, id 0, offset 0, flags [none], proto:
UDP (17), length: 328) 192.168.8.254.67 > 192.168.8.38.68: [udp sum ok]
BOOTP/DHCP, Reply, length 300, xid 0x51d537f3, Flags [ none ] (0x0000)
Your-IP 192.168.8.38
Server-IP 192.168.8.254
Client-Ethernet-Address 50:00:00:00:26:00
Vendor-rfc1048 Extensions
Magic Cookie 0x63825363
DHCP-Message Option 53, length 1: Offer
Server-ID Option 54, length 4: 192.168.8.254
Lease-Time Option 51, length 4: 86400
Subnet-Mask Option 1, length 4: 255.255.255.0
Default-Gateway Option 3, length 4: 192.168.8.254
Domain-Name-Server Option 6, length 8: 192.168.8.50,80.10.246.2
The fact that it is seen by tcpdump means that WLAN card (or whatever other
link is used) _did_ receive the packet.
> On Wed, 18 Jun 2008, SAMUEL Dinesh wrote:
>
> > My DHCPD server is:
> > * Running under Linux Debian
> > * version : Dhcp 2.0pl5-19.1
>
> Is this a Debian sarge (oldstable) or woody (even older) distribution?
> I do no longer have access to anything like that.
>
> Did you check the "non-working" version with another dhcp-server?
> What arch are you using?
>
> I see no such problems when using Debian etch dhcp3-server 3.0.4-13,
> some misterious m$ dhcp server, dnsmasq various versions, udhcpd
> 0.9.8cvs20050303-2.
>
> Is the mac address 50:00:00:00:26:00 the real thing or just an
> obfuscation?
>
> Maybe that BPF filter should be made into an option.
My wild guess is that BPF filter assumes some specific Ethernet frame format,
and unfortunately there are several of those. And especially in wireless LAN world
it's still incredibly messy. (I've been there. I was developing a wireless driver).
That explains how BPF filter works for Alexander with one WLAN device but doesn't
work with another: the second device translates WLAN frames into different
Ethernet frame format!
Read here:
http://en.wikipedia.org/wiki/Ethernet
"Ethernet frame types and the EtherType field" section.
--
vda
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