DHCP + NAT port forwarding = does NOT work ??


W

Wolfgang Hercker

As far as I know a LAN with a DHCP router AND NAT port forwarding does never work.

For NAT port forwarding rules the router need to know to which target computer (=target IP)
he should forwarding incoming requests. Because of DHCP the target computer can be assigned
a dynamic, from time to time changing IP. Hence there is no fixed IP for the NAT rule
which can be entered.

On the other hand a computer name like "comp123" cannot be antered in the NAT forwarding scheme
because only IPs are allowed.

Finally DHCP and NAT port forwarding exclude each other.

Am I right or is there a workaroud ?

Wolfgang
 
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C

Conor

As far as I know a LAN with a DHCP router AND NAT port forwarding does never work.

For NAT port forwarding rules the router need to know to which target computer (=target IP)
he should forwarding incoming requests. Because of DHCP the target computer can be assigned
a dynamic, from time to time changing IP. Hence there is no fixed IP for the NAT rule
which can be entered.

On the other hand a computer name like "comp123" cannot be antered in theNAT forwarding scheme
because only IPs are allowed.

Finally DHCP and NAT port forwarding exclude each other.

Am I right or is there a workaroud ?

Set a static IP address on the target computer running the service you
want. THe DHCP service will see this and not assign it or you can give
it something like 192.168.0.2 and set the DHCP to only assign IP
addresses from 192.168.0.3 to 192.168.0.254.

My Netgear router however always assigns the same IP address to the
same MAC address so for me it's a non issue.

--
Conor

I'm really a nice guy. If I had friends, they would tell you.

Earn commission on online purchases, £2.50 just for signing up:
http://www.TopCashBack.co.uk/Conor/ref/index.htm
 
B

Bob Willard

Wolfgang said:
As far as I know a LAN with a DHCP router AND NAT port forwarding does never work.

For NAT port forwarding rules the router need to know to which target computer (=target IP)
he should forwarding incoming requests. Because of DHCP the target computer can be assigned
a dynamic, from time to time changing IP. Hence there is no fixed IP for the NAT rule
which can be entered.

On the other hand a computer name like "comp123" cannot be antered in the NAT forwarding scheme
because only IPs are allowed.

Finally DHCP and NAT port forwarding exclude each other.

Am I right or is there a workaroud ?

Wolfgang

My SOHO router is the DHCP server and does NAT between the LAN and WAN
sides. Works fine.

In reality, DHCP usually has very stable IPA assignments; when a DHCP
client's lease is nearly due to expire, it asks the server for a new IPA,
and usually gets the same one. Hence, NAT is not affected very often, and
only briefly when the IPA does change.
 
L

Leythos

As far as I know a LAN with a DHCP router AND NAT port forwarding does never work.

For NAT port forwarding rules the router need to know to which target computer (=target IP)
he should forwarding incoming requests. Because of DHCP the target computer can be assigned
a dynamic, from time to time changing IP. Hence there is no fixed IP for the NAT rule
which can be entered.

On the other hand a computer name like "comp123" cannot be antered in the NAT forwarding scheme
because only IPs are allowed.

Finally DHCP and NAT port forwarding exclude each other.

Am I right or is there a workaroud ?

for most of the cheap NAT devices, their DHCP service does not permit
DHCP Reservations - so, that means that for your forwarding to always
work, you have to give the LAN NODE a fixed IP in the LAN. People do
this all the time, all you need to do is give the device a LAN IP, setup
the DNS (for the ISP's numbers if you want it to browse the web) and
then setup forwarding for that.

If your device supports DHCP Reservations, then you only need assign the
MAC address to an IP address and that device will always be issued the
same IP from the DHCP Pool.

DHCP and Port Forwarding have nothing to do with each other, they are
not exclusionary.

I have DHCP and Port Forwarding, but I only forward to the nodes with a
reservation or a fixed IP.
 
G

Guest

Check this registry setting to see if computers are enabled for forwarding

IPEnableRouter
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0 or 1 (False or True)
Default: 0 (False)
Description: Setting this parameter to 1 (True) causes the computer to route
IP packets between the networks that it is connected to.

or if this doesnt help then take a look at this article.

http://www.microsoft.com/technet/prodtechnol/winxppro/deploy/nattrnsv.mspx
 
J

John

Wolfgang Hercker said:
As far as I know a LAN with a DHCP router AND NAT port forwarding does
never work.


Finally DHCP and NAT port forwarding exclude each other.

Am I right or is there a workaroud ?

Wolfgang

Configure the router's DHCP server to assign IP addresses
based on the MAC address of the requesting computer.
The computer always gets the same IP address and NAT
port forwarding works fine.

Some routers do not have that capability.
I don't buy those routers.
 
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P

Phillip Windell

You are right.
Although there is no "real" term of "Port Forwarding". As just an
FYI,...the ports aren't being forwarded,..the ports aren't going anywhere or
doing anything. This is "slang lingo" created by the SOHO market back when
they decided to call Broadband Routers "routers" when they are not really
routers. The real thing that is happening is that the IP#s are being
statically translated "backwards" to a host behind the NAT device,...so this
is called "Static NAT" when the ports at both ends are the same. If the
ports at both ends are different then it is called Static NAT with PAT
(Static NAT combined with Port Address Tranlation).

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/ISA2004_AccessRules.html

Troubleshooting Client Authentication on Access Rules in ISA Server 2004
http://download.microsoft.com/download/9/1/8/918ed2d3-71d0-40ed-8e6d-fd6eeb6cfa07/ts_rules.doc

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/techinfo/Guidance/2004.asp
http://www.microsoft.com/isaserver/techinfo/Guidance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp

Deployment Guidelines for ISA Server 2004 Enterprise Edition
http://www.microsoft.com/technet/prodtechnol/isa/2004/deploy/dgisaserver.mspx
 

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