> From: David S. Miller [mailto:davem@redhat.com]
> I want to understand why on some boots it's on while on some
> boots it is off, that makes no sense.
>
> Before the piece of code you patched, we call ops->create() which is
> inet_create in net/ipv4/af_inet.c, there is sets the PMTU discovery
> disposition based upon the setting in ipv4_config which should always
> have the same setting at the point during boot, every boot.
>
> You need to figure out why it sometimes gets set and sometimes does
> not, then we can figure out how to fix it.
Yes, I see your point. I guess I made an incorrect assumption about it
being changed between reboots. It could be related to routing or something
instead. I'll have to dig a bit further to find a pattern.
However, even if I *do* find the pattern, I still think it is reasonable
to turn off PMTU discovery for ICMP explicitly, instead of based on the
setting of ipv4_config:
1) The setting for the one global ICMP socket gets set once and for all
at initialization time and doesn't track the setting of ip_no_pmtu_disc.
2) Even if it *did* track ip_no_pmtu_disc, the missing per-protocol
granularity of ip_no_pmtu_disc means that you couldn't have PMTU discovery
enabled for TCP, while having it disabled for ICMP.
3) I don't see any reason for wanting to do automatic PMTU discovery for
ICMP packets; normally they are only sent once, and you'll risk it being
dropped somewhere along its path if the DF bit is set.
Svenning
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This archive was generated by hypermail 2b29 : Sat May 05 2001 - 10:23:41 EDT