[Dnsmasq-discuss] disable PMTU discovery

Simon Kelley simon at thekelleys.org.uk
Mon Jan 14 17:05:53 GMT 2008

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?

 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.



More information about the Dnsmasq-discuss mailing list