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You may already be aware, but TFTP - like FTP - is not a NAT
friendly protocol and requires a helper or ALG to inspect the
control channel in order to open up and translate the connections
used by the data channel (which use unrelated high numbered UDP
ports). If TFTP is not working when NAT is enabled, it sounds like
that modem does not have a TFTP ALG included or enabled. I have no
experience with that model personally, but it's not a unique
problem. Workarounds are to not use NAT, purchase a better NAT
router, define a DMZ host, or use a NAT friendly protocol like SCP.
<br>
<br>
Sorry about SIP. That's also not a NAT friendly protocol, and while
some of the same workarounds still apply there are generally not
numerous or better alternatives like there are for file transfer
protocols that replace FTP/TFTP.<br>
<br>
--Blake<br>
<br>
<div class="moz-cite-prefix">Mike Hammett wrote on 3/25/2019 12:18
PM:<br>
</div>
<blockquote type="cite"
cite="mid:2079383401.5744.1553534308903.JavaMail.mhammett@ThunderFuck">
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<div style="font-family: arial,helvetica,sans-serif; font-size:
10pt; color: #000000">Have any of you seen the Comcast XB6 modem
blocking TFTP and some SIP requests?<br>
<br>
We put the modem into bridge mode and TFTP requests are
successful. Reset it, set security to the lowest setting,
disable the firewall... no TFTP requests pass.<br>
<br>
Modem\Router - cable - laptop.
<div><br>
</div>
<div>Of course we can't call into support because the customer
is out of town and thus we're unable to authenticate ourselves
to support (not that we tried).<br>
<br>
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