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Some Networking Questions

Community Veteran
Posts: 1,128
Thanks: 8
Registered: ‎28-08-2007

Some Networking Questions

At the risk of being accused of double posting  Roll eyes http://community.plus.net/forum/index.php/topic,89234.0.html thought I'd post a few questions in here where I should have possibly been in the first place.
I'm trying to clear up a few networking grey points, I have done lots of searching this isn't my first port of call but what I read is so conflicting.
I'll start at the beginning I suppose, firstly DHCP, when your intending to set up all your devices on static IP's is there any point in having it running on the router?
Issuing IP's, is there any advantages/disadvantages to setting the router to issue the same ip to each LAN device. When setting static IP's from the router should the device be set to get it's ip auto or input it manually?
The DMZ zone, does this need to have an ip address outside of the LAN ip's and does it conflict with ports forwarded to other devices if you have two devices using the same ports?
I have been using UPNP at the moment while looking for answers, I notice in my router logs that when I try to switch on two devices that require the same ports to be opened it deletes the forwarding from the first device so I assume UPNP is not the way forward.
I would appreciate any true or false on the above please if possible, it seems when I search the web for answers it all comes down to who you read last  Grin Surely having two devices running at the same time needing the same ports is not uncommon on larger networks.
I've re-booted my router that many times I've actually had my ip profile lowered  Sad.


2 REPLIES
Community Veteran
Posts: 14,469
Registered: ‎30-07-2007

Re: Some Networking Questions

Numbering your questions would help in answering  Wink
As long as you allocate your static IPs outside of the DHCP range then it does not matter whether you have DHCP on or not. You also don't need to worry about any clashes and thus no need to allocate the IPs in the router. I always set-up my PCs with the manual config of static IPs rather than reserve and allocate from the router.
DHCP can be useful when adding new devices for the first time, and also if you have other laptops or friends round who want to connect to the net. It does no harm in having DHCP enabled as long as you follow the advice above.
DMZ normally allocates / routes to an IP address outside your normal LAN IP range. If you used an IP address within your normal LAN you may not get the protect a DMZ normally gives. So, if you normal lan is 192.168.1.X use 192.168.2.100 (say) for the DMZ machine.
You can only port forward a port to a single IP address. If you wanted to have a web server (port 80 say) on the DMZ then you can only forward port 80 to the DMZ IP, it can't also be forwarded to another local lan IP. This is because the routing is actually like a pipe connecting external IP:port -> internal IP:port, the pipe can only go to one place. This is why UPNP will only allow one internal LAN IP to have a port forwarded to it, and it will always be the last PC requesting the port forwarding via UPNP that gets it..
If you need to port forward a single port to more than one internal IP (i.e. you want to run 2 web servers) you need multiple external IPs.

Community Veteran
Posts: 1,128
Thanks: 8
Registered: ‎28-08-2007

Re: Some Networking Questions

Thank Peter, that's really has cleared up some misconceptions of mine. I was not aware that when issuing statics they should be outside of the DCHP range as well as the DMZ. I have always given my devices ip's from within the DHCP range but made the range only give out enough IP's for the equipment I have then mad them static. I suppose if DHCP in disabled it isn't going to try and give out them ip's anyway. I will do as you suggest.
Quote
Numbering your questions would help in answering

1.  Roll eyes only joking m8,  Smiley When I have been looking for information it seemed that the more networking savvy people were saying the same as you.
All the posts I have seen regarding issues like mine don't get an explanation.
It was blowing my mind that people out there are forwarding the same port to separate devices without an extra public ip and it was working when it quite obviously shouldn't. They are probably kidding themselves and have some problems they think are not related.