[Dnsmasq-discuss] disable PMTU discovery

[Simon Kelley]

Bodo Bellut wrote:
> Hi,
> 
> [snip]
> 
>>> For another PXE client I have to disable PMTU discovery on the machine 
>>> running dnsmasq (known Intel LANDesk problem). Do you think there's a 
>>> solution to this without globally disabling PMTU discovery?
>>>
>> A new area for me:
>>
>> http://www.linux.com/base/ldp/howto/Adv-Routing-HOWTO/lartc.cookbook.mtu-discovery.html
>>
>> seems to indicate that it's possible to do it for a subnet (and maybe an 
>> individual host) using the routing table. Is that the sort of thing you 
>> mean?
> 
> This would be an option. I just found another solution in the Squid 
> sources to disable PMTU discovery on a connection basis:
> 
>    int i = IP_PMTUDISC_DONT;
>    setsockopt(conn->fd, SOL_IP, IP_MTU_DISCOVER, &i, sizeof i);
> 
> If you could put this in, too, I'd be more than happy.
> 
> cu, Bodo

I did a bit of Googling for this and I'm confused. Which sockets are
going to need the PMTU disabling?

http://www.faqs.org/docs/Linux-mini/Remote-Boot.html
 Implies both DHCP and TFTP. That gives a bit of a problem, since
there's not easy way to selectively do it for some hosts when they do TFTP.

Then man 7 ip implies that PMTU discovery is off by default for UDP
sockets anyway.


Cheers,

Simon.