On Fri, 16 May 2003 23:16:03 -0300 (EST) Felipe Massia Pereira <massia@ic.unicamp.br> wrote: [on LKML] | Hello, | | I've been searching for the exact meaning of this variable through | Documentation and I've found just empty descriptions (to be filled in, in | Advanced Linux Routing HOWTO, and nothing also in | Documentation/networking/ip-sysctl.txt). I've tried also to read the | kernel source code (net/ipv4/route.c) but I could not figure out what they | mean. What kernel version? And this question would be better asked/answered on either linux-net or netdev mailing lists, so I've replied to those. It (ip_rt_mtu_expires variable) appears not to be used very much. | I've came accross this var because we want to do some experiments in class | with Path MTU discovery. But it happens that MTU is recorded between | experiments (and it's what we expect: that the stack does not do a PMTU | every time). BTW where is the PMTU value kept? Is MTU value recorded for | each destination or for each route? | | So it would be nice if we could make the value found in a experiment to be | forgotten by the kernel so the students could execute the ping several | times. (ping -c 2 -m want ...) Is mtu_expires what we're looking for? Maybe someone else can answer this... | We tried to "echo 1 > /proc/sys/net/ipv4/route/mtu_expires" considering | that it's expressed in seconds. The usual value is 600. But I've read that | it's expressed in jiffies. Jiffies occur 100 times per sec on a PC, is it? | So the value 600 on a PC means 6 seconds? In 2.4.x there are 100 jiffies / second on a PC (x86 arch). However, /proc/sys/net/ipv4/route/mtu_expires is hiding this HZ conversion factor from us, so that the value is expressed in seconds and not in jiffies, so 600 is 600 seconds = 10 minutes. -- ~Randy - : 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
