MTU not regrowing?

[Charles Swiger]

Hi--

On Jun 24, 2014, at 11:43 AM, Andrea Venturoli <ml at netfence.it> wrote:
> Hello.
> 
> Today I experienced something weird (at least for me) on a 8.4 system:
> 
> _ the system had vlan3 interface, with default MTU (1500 bytes);
> _ "ping -D -s 1400 somehost" would work, but "ping -D -s 1500 somehost" would yield "frag needed and DF set" (forgive me if the message is not exact, I don't have it anymore);
> 
> _ to make some tests I reduced MTU size with "ifconfig vlan3 mtu 500";
> _ now, of course, "ping -D -s 400 somehost" would work, but "ping -D -s 500 somehost" would yield "frag needed and DF set";
> 
> _ then I raised MTU again with "ifconfig vlan3 mtu 1500" (notice ifconfig would actually report this as "mtu 1500" was shown);
> _ however the results were as before, i.e. "ping -D -s 400 somehost" would work, but "ping -D -s 500 somehost" would yield "frag needed and DF set";
> 
> _ no way I could ping with a packet bigger than 500 bytes until I rebooted.
> 
> Is this expected behaviour? Any way to get around this?

Does "ifconfig vlan3 down; ifconfig vlan3 up" do any good?
Or that run against the physical NIC?

What is the ethernet HW; and are you using VLAN_HWTAGGING capability?

Regards,
-- 
-Chuck