Date: Tue, 24 Jun 2014 21:03:33 +0200 From: John Hay <jhay@meraka.org.za> To: Andrea Venturoli <ml@netfence.it> Cc: freebsd-net@freebsd.org Subject: Re: MTU not regrowing? Message-ID: <20140624190333.GA13748@zibbi.meraka.csir.co.za> In-Reply-To: <53A9C6D0.3090900@netfence.it> References: <53A9C6D0.3090900@netfence.it>
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On Tue, Jun 24, 2014 at 08:43:28PM +0200, Andrea Venturoli 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? Do a "route get somehost" and see what mtu is returned. You might be able to delete or tweak that route. John -- John Hay -- jhay@meraka.csir.co.za / jhay@meraka.org.za
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