[avahi] Record too large, cannot send

Christiano F. Haesbaert haesbaert at haesbaert.org
Fri Sep 23 09:54:27 PDT 2011

On 23 September 2011 13:37, Harvey, Edward <Edward.Harvey at analog.com> wrote:
>> From: avahi-bounces+edward.harvey=analog.com at lists.freedesktop.org
>> [mailto:avahi-bounces+edward.harvey=analog.com at lists.freedesktop.org]
>> I am running Ubuntu Oneiric (beta 1) amd64, fully updated
>>       netatalk 2.2~beta4-1
>>       avahi-autoipd 0.6.30-4ubuntu1
>>       avahi-daemon 0.6.30-4ubuntu1
>>       avahi-utils 0.6.30-4ubuntu1
>> Trying to configure server as a time machine server.  Working great so far,
>> but only up to 20.  As soon as I add the 21st share, they all disappear.  I can
>> still connect to the shares via netatalk (go into Finder, type in
>> afp://tmserver), but the bonjour/avahi information disappears, so the target
>> no longer appears in the Time Machine "Select Disk" dialog.
>> When I watch the syslog with 20 versus 21 shares enabled in netatalk, the
>> following is the clear differentiating factor.  At 21 users, I get this message:
>> Sep 23 05:17:40 tmserver avahi-daemon[1042]: Record too large, cannot send
>> Any ideas how to resolve this problem?
> I tracked this down through the source code, and found the AvahiDnsPacket has a property called max_size, which gets set based on the system mtu.  So I changed the system mtu (tried increasing from 1500 to 1600) and restarting avahi-daemon and netatalk...
> The log message disappeared (No more avahi-daemon "Record too large, cannot send" appearing in the syslog) but the client still cannot see the server with 21 shares or more.  (Again, yes can browse afp:// but no, does not populate list via bonjour)
> So I'm hoping someone might have some more useful information or suggestions...

Avahi should be able to fragment the packet before IP fragmentation,
if it doesn't it's a bug.
It's in the mdns draft.

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