udhcpc in 1.10.3 doesnt like my WLAN card

[SAMUEL Dinesh]

Hello,

Hope you remember that the probleme I have is not on a Wireless Card. 
The kernel and all the tools that I am using are not fancy tools.

The probleme must come from 'BPF filter' hecause when I comment this line
the DHCPC works correctly:




-----Message d'origine-----
De : busybox-bounces at busybox.net [mailto:busybox-bounces at busybox.net] De la
part de Denys Vlasenko
Envoyé : jeudi 19 juin 2008 20:58
À : busybox at busybox.net; Cristian Ionescu-Idbohrn; Alexander Griesser (LKH
Villach)
Objet : Re: udhcpc in 1.10.3 doesnt like my WLAN card

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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