[clue-tech] A port triggering application.

[chris fedde]

my router (also some linksys or other) has a "dmz host" configuration
that I use for all my external access. I also use dyndns.org's free
service to map my routers external address to a dns name.
all inbound access then gets forwarded to the designated dmz host were
balance and other forwarding rules are kept.

Internaly I use dnsmasq on my "file server" for  dns and dhcp. and
turn that functionality off on the linksys.
dnsmasq is pretty easy to setup for a tiny domain like my home network.

chris

On Wed, Oct 21, 2009 at 3:04 PM, Brian Gibson <bwg1974 at yahoo.com> wrote:
> You really only have 3 options for reserving IPs
>
> 1) Replace firmware with one that has more features
> 2) Disable DHCP and run a separate DHCP server on your network that can reserve IP addresses
> 3) Have the DHCP start IPs at a higher number and reserve the lower block for static IPs
>
>
>
> ----- Original Message ----
> From: David L. Anselmi <anselmi at anselmi.us>
> To: CLUE tech <clue-tech at cluedenver.org>
> Sent: Wed, October 21, 2009 12:45:44 PM
> Subject: [clue-tech] A port triggering application.
>
> So I have a Linksys router doing NAT.  On the inside is an apt repository (HTTP).  On the outside is the apt client.
>
> So you can (and I did) set up port forwarding so the outside clients could get to the inside repository.  But that requires knowing the inside IP address, which changes due to DHCP.  (The Linksys DHCP server isn't smart enough to reserve addresses.  And I'm too lazy to figure out per-network settings so the repository can use a static IP--it changes networks sometimes.)
>
> When I went to change the port forwarding I noticed the port triggering page.  When the router sees a connection going out to a port it opens a port for incoming connections (sort of a temporary port forward).  The nice thing is that it handles the address for you so it won't break when the DHCP lease changes.
>
> What port should I use to trigger opening port 80?  Well, it's easy to send random packets to random ports (nc(1)), so maybe something like discard (I don't think the port has to be open on the outside machine).  I wonder how long the triggered port stays open?  Times out after outgoing traffic, or incoming?
>
> Oh, wait.  I always use apt over SSH so I'll just trigger on that. Works like a charm.
>
> (What I really need is time to put real firmware on the Linksys and then I wouldn't need silly workarounds.  And some more machines so economies of scale would make it worth setting up LDAP and a more automated configuration process.)
>
> Thanks for listening.  It's nice to fool with networking while the snow falls.  I'll go back to work tomorrow and stop bothering you.
>
> Dave
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