[mythtv-users] Residential DHCP (was: Re: Help debugging failed HDHR recordings)

[Jay Ashworth]

----- Original Message -----
> From: "Julius Roberts" <hooliowobbits at gmail.com>

> I heard recently
> (http://www.mythtv.org/pipermail/mythtv-users/2011-January/307965.html)
> that you're supposed to add the HDHR to myth using it's device ID, not
> via it's ip address. I was having an issue with recordings being cut
> short prematurely, this fix seems to have worked for me.

This seems like as good a time as any to make a somewhat obscure point, that 
may be relevant to that exchange:

On a residental RFC 1918 network, IP addresses are commonly assigned by
a DHCP server *inside your edge router*.  Most consumer routers *do not* have 
NVRAM caching for that sort of parameter, and therefore don't keep a local
list of the leases they hand out.

Some devices will attempt to request the last IP they had, some won't.

The router will hand out the last IP address it knows it gave a specific
requesting device by MAC address... *as long as you haven't shut it off*.


                 ====================================
When you power off a residential router that provides DHCP to internal 
devices, you really, *really* ought to reboot them as well, or request
a fresh address on their behalf ("ipconfig /renew" on WinXP, frex).
                 ====================================

If you don't, lots of things can get confused, because devices' IP addresses
are almost guaranteed to change from what they were before.

Routers running aftermarket code like Tomato, DD-WRT or OpenWRT likely
don't cause this problem, nor will commercial routers like SnapGear's;
those *do* generally cache their leases locally (I think).

While I'm on this topic, remember that if you swap your router out, you
also generally have to power cycle the cable/DSL modem it's plugged into;
*many* carriers MAC-lock those to the first MAC they see on power up.

The failure mode there is "unexpectedly just won't pass packets at all".
so it can be hard to diagnose -- even if you do this for a living.

That is all.

This was a recording.

Cheers,
-- jra