[mythtv-users] Schedules Direct Download Failures
Mike Hodson
mystica at gmail.com
Tue Feb 10 18:21:59 UTC 2015
On Feb 10, 2015 10:58 AM, "R. G. Newbury" <newbury at mandamus.org> wrote:
> I don't think that the problem really relates to the DNS server. I think
it has something to do with how the cableco's gateway initializes the new
link from your router, to the rest of the network (a port has been closed,
and is not re-opened???)
>
> Some thing seems to be lost such that your cableco/ISP's setup does not
immediately recognize the need for a DNS lookup of the SD IP address or
does not know where to request the IP address.
>
> But things wake up when ping comes calling!
> But also note that ping uses ICMP, NOT tcp or udp.
>
What this sounds like is a TCP connection being left open without any data
sent, for long enough that a NAT 'forgets' the connection is still alive.
Perhaps Rogers is starting to use some form of carrier-grade-nat
implementation primed for when they run out of ipv4 allotment, and ARIN
says 'no'. Although, this is unlikely, as the time out is on a wholly new
connection and not one I would expect to be kept open and idle like ssh.
Another potential is that perhaps DNS from their server actually is
overloaded and times out for a short period during which the script may
also timeout? I imagine most people configure their servers to use NTP...
The synchronization of numerous mythtv boxes all connecting probably looks
like a mini-ddos on the DNS and web services both...
If you're able to get a packet capture with tcpdump when this happens, it
may be able to [dis]prove some theories.
Mike
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