Enable port forwarding clears DHCP client table

[Travis Spencer]

Hey,

I enabled port forwarding from my DSL modem to my wireless router. Then I
enabled it to all my boxes. This second step cleared the router's DHCP
client table. None of the machines show up there any more. Is this normal?
They all seem to work, internet works, etc. Just wondering if I should be
concerned.

Regards,

Travis Spencer
Portland, OR. USA

 

[James Egan]

I enabled port forwarding from my DSL modem to my wireless router

It must be more than a modem if it can do this. What type of modem and
router do you have?


Jim.

 

[Travis Spencer]

Well the "modem" is a actiontec 1524 router, but I only use it as a modem
because I have a linksys wireless-B AP (BEFW1154). I enabled port
forwarding of 113 from the actiontec to the linksys. Then I enabled 113
from the linksys to all my boxes. Doing this cleared the DHCP client table.
Does this matter? Is this a sign of problems to come?

Thanks for the response, Jim.

 

[James Egan]

Well the "modem" is a actiontec 1524 router, but I only use it as a modem
because I have a linksys wireless-B AP (BEFW1154). I enabled port
forwarding of 113 from the actiontec to the linksys. Then I enabled 113
from the linksys to all my boxes. Doing this cleared the DHCP client table.
Does this matter? Is this a sign of problems to come?

You want to avoid a setup with two nat devices. I would disable the
routing and dhcp functionality of the linksys and just use it as a
hub/switch. Let the actiontec do the natting and dhcp.


Jim.

 

[Travis Spencer]

Hey James,

That messed things up a bit. None of my boxes could automatically obtain an
IP address after I disabled nat on the linksys. I would give them static
IPs, but my laptop needs a dynamic IP so it can connect to other networks
when I am out and about. Why are two nat devices bad? Should I configure
the linksys to use a static IP and disable nat on the ActionTec?

TIA.

 

[James Egan]

That messed things up a bit. None of my boxes could automatically obtain an
IP address after I disabled nat on the linksys. I would give them static
IPs, but my laptop needs a dynamic IP so it can connect to other networks
when I am out and about. Why are two nat devices bad? Should I configure
the linksys to use a static IP and disable nat on the ActionTec?

Well you don't want none or two dhcp servers just like you don't want
none or two nat devices so if you switch dhcp and nat off on the
linksys then they must both be enabled on the ActionTec.

Give the linksys a static address on the same network as but outside
the dhcp address pool of the ActionTec.

The Actiontec needs to be running as the nat device since that's the
one which knows the external ip address and uses it to replace the
private addresses.

It doesn't matter which runs as the dhcp server as long as the one not
running as the dhcp server is given a static address on the same
network outside the address pool range.

Is it bad to have two nat devices? I don't know if there'll be
problems, but it's an extra route and function being performed which
is unnecessary.


Jim.

 

[Travis Spencer]

Give the linksys a static address on the same network as but outside
the dhcp address pool of the ActionTec.

Jim, can you elaborate on this for me? If the ActionTec's IP is 192.168.0.1
(on the LAN) then I should assign the address 192.168.0.2, for example, to
the Linksys. Would this IP be "outs the dhcp address pool of the
ActionTec?"

Regards,

Travis Spencer
Portland, OR. USA

 

[James Egan]

Jim, can you elaborate on this for me? If the ActionTec's IP is 192.168.0.1
(on the LAN) then I should assign the address 192.168.0.2, for example, to
the Linksys. Would this IP be "outs the dhcp address pool of the
ActionTec?"

If the netmask used on your network is 255.255.255.0 (which it
probably is) then the range of valid addresses on the network will be
192.168.0.1 to 254

Somewhere in the (dhcp) setup of the actiontec there will be a range
of addresses which you can set which it will use to allocate to
computers joining the network.

So if the actiontec is 1 and the linksys is 2 then you can change the
dhcp pool to be anything from 3-254

The important point is that everything must have it's own specific ip
address on the network so you have to ensure that the dhcp server
doesn't issue to a computer the same number as you have statically
assigned to the linksys device.


Jim.

 

[Travis Spencer]

Hey Jim,

I tried to disable the Linksys' nat and DHCP stuff tonight, but I couldn't
get it working. I think this is one of those times when a picture is worth
a thousand words. I have uploaded screenshots of the ActionTec, Linksys,
wireless clients, and hardwired clients' configurations to my web site.

The ActionTec:
http://www.aracnet.com/~tspencer/temp/net/actiontec/

The changes that I tried to make to the Linksys that didn't work can be seen
here:
http://www.aracnet.com/~tspencer/temp/net/brk_linksys/

The Linksys works with these settings:
http://www.aracnet.com/~tspencer/temp/net/linksys/

The wireless clients are configured like this:
http://www.aracnet.com/~tspencer/temp/wireless_conf/

The wired client is configured like this:
http://www.aracnet.com/~tspencer/temp/wired_conf/

Basically, with the changes that I made, I was able to ping all the
computers on the network and the Linksys; however, the modem was not
accessible. I couldn't ping it.

Thanks for the help w/ this.

Regards,

Travis Spencer
Portland, OR. USA

 

[James Egan]

Basically, with the changes that I made, I was able to ping all the
computers on the network and the Linksys; however, the modem was not
accessible. I couldn't ping it.

Looking at the Actiontec dhcp gif, it is not immediately evident if or
how to change the dhcp pool. It will probably be in the manual but it
doesn't matter which is the dhcp server and the linksys has
configurable settings. So just disable dhcp on the actiontec and
enable it on the linksys.

Also you need to give a static address to the machine which is running
the service on port 113.

So to summarise

The actiontec has an ip address of 192.168.0.1. dhcp server now
disabled. Change the port forwarding setting which currently forwards
113 to 192.168.0.2 (linksys) to 192.168.0.3 (the 113 service
computer).

The linksys has an ip address of 192.168.0.2 dhcp server now enabled.
Set the dhcp server starting address to 192.168.0.4, set the number of
users appropriate for you network.

The machine running the service on 113. Give it a static address of
192.168.0.3 to match the address you have told the actiontec to
forward to.

That's about it. Your Internet ip address on the Linksys is currently
the same as the LAN address. I don't suppose it will matter since the
Internet interface of the Linksys is unused. Better to leave these
settings blank just in case.


Jim.

 

[James Egan]

That's about it. Your Internet ip address on the Linksys is currently
the same as the LAN address. I don't suppose it will matter since the
Internet interface of the Linksys is unused. Better to leave these
settings blank just in case.

Oh. And as the port 113 serving machine has a static address you will
have to change other tcp/ip settings to enable dns, use 192.168.0.1 as
the default gateway and 192.168.0.1 for domain name server. Or you
could enter your isp's nameservers here.

All this information will be passed to the other computers via dhcp.


Jim.

 

[Travis Spencer]

Hey Jim,

I gave it another try on Saturday morning, but I ran in the same problem: I
could communicate across the network through the Linksys, but the ActionTec
was unavailable. I am going to force myself to spend a day at the library
this week and read about routing, switching, tcp/ip, and stuff. Surely, I
will have a better luck if I have a deeper understanding of the technology.
I appreciate the help; it has been extremely nice of you to coach me through
this!

Regards,

Travis Spencer
Portland, OR. USA

 

[James Egan]

I gave it another try on Saturday morning, but I ran in the same problem: I
could communicate across the network through the Linksys, but the ActionTec
was unavailable. I am going to force myself to spend a day at the library
this week and read about routing, switching, tcp/ip, and stuff. Surely, I
will have a better luck if I have a deeper understanding of the technology.
I appreciate the help; it has been extremely nice of you to coach me through
this!

That's a bit of a mystery. Everything (that's wired) should be plugged
into normal ports on the linksys. The Internet port should be
unconnected. If you originally had the actiontec operating out of the
linksys' Internet port, that cable might be a crossed one. Try
switching the cables round a bit and see what's pingable and what's
not.


Jim.

 

[Travis Spencer]

I never thought to take the ActionTec out of the Linksys' Internet port.
Doh! I will try this again in a couple of days. I will keep you posted.

Thanks, Jim.