dhclient doing DISCOVER with bad IP checksum - bge

[Brooks Davis]

On Mon, Dec 01, 2008 at 12:27:58AM -0800, Jonathan Feally wrote:
> Sorry for the cross-post, but this could be either lists problem.
> 
> I have 2 boxes running 7-STABLE as of 20081130, both i386 SMP. One is 
> running ISC DHCPD 3.0.x from recent ports, and the other dhclient from make 
> world.
> 
> The server is refusing to answer the DISCOVER request, as it thinks the IP 
> checksum is wrong, which tcpdump also confirms. Other DHCP clients are 
> working fine on this network, so I do not believe it to be the network, 
> server or dhcpd.
> 
> Server is running a 2 Port Intel card - em driver.
> 
> Client is a Dell PE1750 with 2 onboard NIC's - bge driver.
> 
> I have tried turning off both RXCSUM and TXCSUM on both the client and 
> server machines with no luck. I also tried the second NIC on the server 
> with the same result.
> 
> This setup was working just a couple of weeks ago, and the only thing that 
> has changed is updating the src for a make world. PXE booting this server 
> does result in an IP being issued, so it is pointing towards something 
> new/changed in 7-STABLE.
> 
> I have attached a 3 packet dump of the DISCOVER requests.
> 
> Can anybody shed some light on this for me?

Where are you running tcpdump?  If on the host with the bge0 device,
the checksums are probably useless due to checksum offloading.  They
should be valid on the server end of things.

You might try disabling checksum offloading on the nic and see if that
changes the results.

It's possible the change to bpf.c to send packets through a socket when
reassociateing isn't working correctly in that case.  You might try
backing out this change and seeing if the problem goes away (this will
cause problems on some networks).

http://svn.freebsd.org/viewvc/base/stable/7/sbin/dhclient/bpf.c?revision=178675&view=markup

-- Brooks
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