[mythtv-users] Schedules Direct Download Failures

[R. G. Newbury]

On 10/02/15 10:49 AM, Dan Wilga wrote:
> On 2/9/15 3:22 PM, john.baab at gmail.com wrote:
>> I'm having issues where my SD fails on most attempts, logs indicate a
>> download error: http://paste.ubuntu.com/10147508/
>>

>> I have verified this isn't a user error, it runs fine as my user and
>> if I su to the mythtv user as well.  Not sure where else to look now.
> I was having a problem where the first attempt after a long pause (an
> hour?) would fail, but if I tried again after a failure it would work.
> At the suggestion of others on this list, I ended up using this script
> as a wrapper around mythfilldatabase proper, and have not had any
> problems since:
>
> #!/bin/sh
> ping -c 3 dd.schedulesdirect.org
> /usr/local/bin/mythfilldatabase $*
>
> It makes no sense to me that it would be necessary to ping the server
> first, but it does work.

I reasonably sure that the ping workaround was originally my suggestion 
to the list. The failure has nothing to do with mythtv.

I recognized that an attempt would fail if done after some time at idle, 
but would *never* fail when done while I was actively using the system. 
John, you saw that too.
Same thing with a browser: my external 'home page' would never load on 
first attempt after some hours of idle.

There are a couple of places where the fault could arise. I don't think 
that it could be my router's cache, but the usual home router does not 
cache many lookups. You can try switching to a different external DNS 
server (eg OpenDNS at 208.67.222.222 and 208.67.220.220), and if your 
router supports it, turn on DNSmasq, with internal caching enabled and 
'use received dns with static dns' enabled. This makes the cache the 
first reference source, and then the external DNS.

This does seem to speed up general surfing a little bit as it by-passes 
any over-load at your cableco's DNS server.

Unfortunately, the DNS cache in most home routers is limited to about 
150 names, which does not cover much browsing. The grabber 'calls home' 
only once a day, so the DNS cache for SD will have been lost if any 
other computer/phone/tablet has done just about anything on line during 
the day.

The cache at an external static DNS server *may* be large enough to 
respond without having to lookup, but that does not seem to be the 
source of the problem.

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.

Obviously this should not happen. But you can test it on your own setup. 
Set your brower's 'home page' to 'None' so that your browser will not 
initiate any lookups on initialization. Ping and note the IP address of 
some public corporation's web page. First thing in the morning (couple 
of hours of idle), use the public URL to try to pull that home-page, The 
next morning, do the same thing, using the IP address. Compare and 
contrast.

I got NO headway from Rogers Cable about the source or prospective fix 
of the problem.  "Does not exist"...

Geoff
-- 
              R. Geoffrey Newbury			
            Barrister and Solicitor
       Suite 106, 150 Lakeshore Road West
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        t905-271-9600 f905-271-1638
               newbury at mandamus.org