DHCP problem with OFED patch for Infiniband support

[HAUTREUX Matthieu]

Hi,

I'm currently using dhcp-3.0.5 provided by CentOS-5.2 with OFED-1.3 
patch for Infiniband support (enclosed).

Using OFED patch, dhclient is conforming to RFC-4390. It doesn't include 
IB interface harware address in the DHCP packet but uses client 
identifier instead.
As a result, the interface hw address length is 1 (just the character 
corresponding to the type of Addr : 32 ).

One major drawback of DHCP over IB is the requirement to use broadcasted 
replies. The only way for a IB dhclient to find its own reply is by 
looking for matching xid (transaction ID). xid are generated using 
random() in dhclient. random() is initialized using 
srandom(seed+cur_time). Nethertheless, when hw address hlen is 1, the 
processed seed is roughly always the same. As a result, IB nodes that 
uses dhclient to configure IB interfaces at the same time share the same 
xid and as a result use any of the broadcasted replies. The protocol is 
then broken.

I don't know if it is the good place to post that, but you will find 
enclosed a patch that correct this behavior. The proposed patch build a 
"backup seed" using all the interfaces available on the machine and use 
it if it can not find a good seed for the required interfaces during 
real DHCP process. If backup seed construction fails (no interfaces 
providing a hw address long enough for seed construction), it try to 
build a seed using gethostid().

As far as I have tested it, the patch seems to work quite well. I will 
let you judge if it will be interesting to add it to the main branch or 
add your own to ensure that this problem is solved. The modified part of 
the code is still the same in 4.1.0.

If you have any question, feel free to ask.

Thanks in advance
Matthieu Hautreux

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