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The phones also have a very limited arp cache, I believe 16 entries.
ARP entries corresponding to next hop for CM servers are permanently
cached. Recommendation is to avoid deploying phones in such a large L2
domain. I believe this is covered in the UC SRND. There is some
history behind this:<br>
<br>
CSCdt28640 7960 Intermittant Delayed Dialtone when going off-hook<br>
<br>
/Wes<br>
<br>
On Wednesday, June 30, 2010 11:11:18 AM, Pawlowski, Adam
<a class="moz-txt-link-rfc2396E" href="mailto:ajp26@buffalo.edu"><ajp26@buffalo.edu></a> wrote:<br>
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<p class="MsoNormal">Folks,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> I’ve seen some commentary about certain
versions of Call Manager not being suitable to sit directly on a
subnet
with a large number of endpoints due to a limited capacity of the ARP
table,
but, nothing similar from the VoIP telephones themselves.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> I have a large subnet of VoIP
devices, a /19 with over 1500 phones active at this time. Within this
subnet,
and, specifically, within a “building”, subset of network gear,
there are specific telephones which are not able to complete a call to
another
telephone on that subnet, within the “building”. Each of these
devices is direct attached to a Cat 3750G placing the voice traffic on
the sub
mentioned before. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> What I’ve seen in the one
time I was able to isolate the problem, was the one of the two phones
in the
conversation would be continually ARPing for the other device, but, the
other
device, despite seeing it, wouldn’t reply, so the RTP stream never
establishes. I toggled the GARP feature from off, to on (although we
have
phones elsewhere with it off and/or on) and it began working. The
problem still
exists with other, specific, sets, but, the feature is on and swapping
it doesn’t
help. Often, a second try at establishing a call will work. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> I guess what I’m asking
is, is there a limit to the ARP table on the device? Does it even
matter, since
it attempts to lookup the MAC of the target phone on each call ? Anyone
else
had to deal with this ? <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> You’ll see an error in
the device’s console log about 0 RTP packets received, and stream stats
will show no traffic sent or received, but, of course, the phone
presents as
though the call is flowing and thus the end users complain.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks for your insights,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Adam Pawlowski<o:p></o:p></p>
<p class="MsoNormal">University at Buffalo<o:p></o:p></p>
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