On Thu, Mar 28, 2002 at 03:35:20PM +0100, sotto@slb.com wrote: > Hi, all ! > > The problems described with message from March, 27th had been tested more > since yesterday. > > I found that the communication with another computer that uses Reliant Unix > 5.43 (SINIX) works very fine. > No limits for receiving data were found. > > The difference between the SuSE 7.2 linux computer and the SINIX machine is: > The SINIX machine doesn't set the "don't fragment" bit at each acknowledge > datagram, the linux machine does it per default for all datagrams (see > tdump10.txt in mail yesterday). > > I scanned the manuals for this and found setsockopt(). I used it with SOL_IP > and IP_MTU_DISCOVER flag with the optval step by step set to one of the 3 > available values IP_PMTUDISC_DONT, IP_PMTUDISC_WANT and IP_PMTUDISC_DO. > No reaction occurs. > > My question today is: What's the right way to unset the "don't fragment" bit IP_PMTUDISC_DONT is correct, but it'll only affect the socket it is done on. To turn it off globally you can use the ip_no_pmtu_disc sysctl. Another way for TCP is to set a small enough advmss/mtu on the route and flush the routing cache. This usually works around path mtu discovery problems. BTW if you need to do this you likely have a broken firewall somewhere that incorrectly blocks all ICMP. You should complain to the firewall admin. -Andi - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
