[GTALUG] DHCP "hidden feature" / "Easter Egg"

[Lennart Sorensen]

On Mon, Mar 02, 2015 at 01:58:17AM -0500, Walter Dnes wrote:
>   This is what I get for TTFM (Trusting The Fine Manual). I did Google
> and RTFM.  Page 6 of the PDF document at the manufacturer's website...
> http://www.silicondust.com/hdhomerun/hdhomerun_tech.pdf lists the output
> from a "get help" command ***FOR CURRENT MODELS***.  It includes,
> amongst other items...
> 
> /sys/ipaddr dhcp|"<ip> <mask> <gw> <dns>"
> 
>   On my machine, "get help" produces...
> 
> Supported configuration options:
> /ir/target <protocol>://<ip>:<port>
> /lineup/location <countrycode>:<postcode>
> /sys/copyright
> /sys/debug
> /sys/features
> /sys/hwmodel
> /sys/model
> /sys/restart <resource>
> /sys/version
> /tuner<n>/channel <modulation>:<freq|ch>
> /tuner<n>/channelmap <channelmap>
> /tuner<n>/debug
> /tuner<n>/filter "0x<nnnn>-0x<nnnn> [...]"
> /tuner<n>/lockkey
> /tuner<n>/program <program number>
> /tuner<n>/streaminfo
> /tuner<n>/status
> /tuner<n>/target <ip>:<port>
> 
>   There is no mention of "/sys/ipaddr" ***ON MY MACHINE***.  I also
> remember various people asking on the HDHomerun support forum years ago
> about IP addresses, and hearing that this model did not have any other
> addressing options.  One correction on the date of my machine.   See
> https://www.youtube.com/watch?v=JXmi-6nVhCM which discusses the exact
> same model I have.  I bought mine in 2010, but the reviewer notes that
> it won some award at CES2008.  Consider it a 2008 model.
> 
>   Due to the documentation, and lack of mention of DHCP in "get help",
> I assumed it wouldn't work.  However, just for ####s and giggles, I
> enabled the DHCP server on my router, set the DHCP address pool to
> 192.168.123.241-to-192.168.123.247, and expanded my local LAN subnet
> from a /29 to a /28 like so...
> 
> config_eth0="
> 192.168.123.251/28 broadcast 192.168.123.255"
> routes_eth0="
> default via 192.168.123.254 metric 20
> 192.168.123.240/28 via 192.168.123.254 metric 0"
> 
>   Notice the lack of a 'modules=( "!iproute2" )' line.  I installed the
> latest firmware update from the manufacturer's website...
> (hdhomerun_atsc_firmware_20141124.bin).  Lo and behold, it actually
> works, coming up at 192.168.123.241.  This is notwithstanding the
> documentation and "get help" output, which both say nothing about DHCP.
> Maybe this was a feature that was backported into a firmware update.
> Anyhow, I apologize for wasting peoples' time.

Hey we learned something too.

I think the idea always was that it should use dhcp.  Newer models
started allowing static IP, but they all do dhcp.  dhcp is complicated
though and sometimes compatibility issues happen.  When dhcp does not
fail, it is very common to default to a link local address of 169.254.x.x,
which is certainly what windows does, and apparently also what the
HDHR does.

-- 
Len Sorensen