[cisco-voip] New install 11.5 phones won't register or the subscriber

[Derek Andrew]

If both servers are MTU 1500 and the network supports 9000, you should be
good.

On the other hand, if one machine is MTU 1500 and the other is greater, and
the network supports greater, it can send a packet too big for the machine
to receive.

On Thu, Oct 12, 2017 at 12:11 PM, Dave Goodwin <dave.goodwin at december.net>
wrote:

> While I haven't tried to test this specifically, my understanding is that
> a network transport that fully supports jumbo frames (e.g. 9000 bytes) will
> cause no issues with hosts configured with 1500 byte MTU trying to
> communicate. I thought the issues can happen when the configured MTU in the
> two hosts communicating exceeds the effective transport MTU anywhere in the
> path between the hosts.
>
> On Thu, Oct 12, 2017 at 1:48 PM, Mike King <me at mpking.com> wrote:
>
>>
>>
>> On Wed, Oct 11, 2017 at 4:10 AM, Ryan Huff <ryanhuff at outlook.com> wrote:
>>
>>>
>>> - Make sure you’re accounting for any non-standard MTU between the
>>> publisher and subscriber nodes. By default, CUCM will use 1500 if you don’t
>>> change it (which is the typical network standard). For example; If you have
>>> jumbo frame support in the network path between the two nodes and you set
>>> 1500 MTU on the publisher and subscriber, the subscriber installation will
>>> typically “fail node connectivity validation” with no visible clue as to
>>> why. This is because this is the first point in the subscriber installation
>>> where there is enough back/fourth TCP with the publisher to cause the TCP
>>> window to burst, which causes the TCP retransmission error. Since it
>>> happens at this point, CUCM assumes it’s because the publisher can’t verify
>>> the subscriber.
>>>
>>>
>>
>> Hey Ryan,  Do you have links for that?  I find the behavior very odd, and
>> not the way I understood standard MTU over a Jumbo enabled network to
>> function.   Or is this just a Cisco Caveat type deal?
>>
>> Mike
>>
>> _______________________________________________
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>> cisco-voip at puck.nether.net
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>>
>>
>


-- 
Copyright 2017 Derek Andrew (excluding quotations)

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Typed but not read.
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