Can DHCP IP assignment and NAT-Port forwarding coexist ?


W

Wolfgang Hercker

I have an inhouse-LAN with some computers and a router as device to the outside Internet.

I have enabled DHCP IP assignment from the (NetGear) network router to all inhouse computers.

On the other side I want to offer some server/services on one of the computers.
Hence I have to enter some NAT port forwarding rules in the router setup
so that incoming requests from the Internet know to which of
the inhourse computers they should be redirected.

On the other side I see no possibility to define these rules dynamically.
I have to define a fixed IP.
Do I really have to assign the server a fixed IP that I can NAT port forwarding
or is there another work around ?

Wolfgang
 
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K

Kerry Brown

Yes you have to assign the server a static IP. Make sure it is done by
either a reservation on the DHCP server (probably not possible with a
consumer router) or that the IP is outside of the scope of the DHCP server.
For example if the DHCP server assigns addresses in the range 192.168.0.100
to 192,168.0.200 you would pick a static IP not in that range. You also have
to make sure it does not conflict with any other statically assigned IP
addresses like the router itself or a print server.
 
M

Malke

Wolfgang said:
I have an inhouse-LAN with some computers and a router as device to
the outside Internet.

I have enabled DHCP IP assignment from the (NetGear) network router to
all inhouse computers.

On the other side I want to offer some server/services on one of the
computers. Hence I have to enter some NAT port forwarding rules in the
router setup so that incoming requests from the Internet know to which
of the inhourse computers they should be redirected.

On the other side I see no possibility to define these rules
dynamically. I have to define a fixed IP.
Do I really have to assign the server a fixed IP that I can NAT port
forwarding or is there another work around ?

Wolfgang

Static and dynamic IP addresses can be used on the same network without
any problem. For instance, all my network printers have static IP's but
the computers get their IP addresses via DHCP from a router.

Servers should always have a static IP address assigned.

Malke
 
K

Kurt

Wolfgang said:
I have an inhouse-LAN with some computers and a router as device to the outside Internet.

I have enabled DHCP IP assignment from the (NetGear) network router to all inhouse computers.

On the other side I want to offer some server/services on one of the computers.
Hence I have to enter some NAT port forwarding rules in the router setup
so that incoming requests from the Internet know to which of
the inhourse computers they should be redirected.

On the other side I see no possibility to define these rules dynamically.
I have to define a fixed IP.
Do I really have to assign the server a fixed IP that I can NAT port forwarding
or is there another work around ?

Wolfgang

Since Port Forwarding is to a specific IP address, it would be prudent
to make certain that the IP address is always that of the server hosting
the service. A static IP address is the only way to absolutely guarantee
that the IP address won't change after a router reboot, etc. Why are you
so opposed to giving your servers static addresses? It is considered
best practices for servers, printers, etc, to have static addresses.

....kurt
 
J

John Wunderlich

(e-mail address removed) (Wolfgang Hercker) wrote in
I have an inhouse-LAN with some computers and a router as device
to the outside Internet.

I have enabled DHCP IP assignment from the (NetGear) network
router to all inhouse computers.

On the other side I want to offer some server/services on one of
the computers. Hence I have to enter some NAT port forwarding
rules in the router setup so that incoming requests from the
Internet know to which of the inhourse computers they should be
redirected.

On the other side I see no possibility to define these rules
dynamically. I have to define a fixed IP.
Do I really have to assign the server a fixed IP that I can NAT
port forwarding or is there another work around ?

You don't mention which model of NetGear router you have, but most
models have the capability to specify in the Advanced DHCP
configuration that a machine with a given MAC address should always
be given a specific IP address by the DHCP. Using this method, the
"server" machine can still obtain its IP address using DHCP but the
router will always give it the same address. Look for this option in
the DHCP area of your router manual.

HTH,
John
 
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D

Doug Sherman [MVP]

If your router supports reserved IPs based upon MAC address, you can make
the 'server' get the same IP every time.

Doug Sherman
MCSE, MCSA, MCP+I, MVP
 
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