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Multiple Static IPs (servers) and DHCP coexistence

Csaba Gabor
Occasional Visitor

Multiple Static IPs (servers) and DHCP coexistence

HELP! I have a major problem that I only just discovered a week after having installed a BEFSR81 router. My web server is not visible from the outside world anymore!!! I can see it fine from the two PCs on the router, but people from outside cannot ping me (By setting Disable on Block WAN request under Advanced/Filters the Router is visible). I also tried port forwarding of http/port 80 on the fake PC entry in the DHCP table while it's visible, but this didn't help.

A copy of the letter I sent Linksys follows (The linksys tech in the Phillipines refused to let me talk with a superior and said that she would do the checking on my behalf. She said that it was too complicated to explain over the phone, but I should submit my request in writing to Support@Linksys.com), but so far there has been no response. The reason I got the router was that the VoIP phone (ATA-186 from VoicePulse.com) I got requires DHCP. By the way, is there such a beast as a 1 port (DHCP) router? If I really do have to throw the BEFSR81 back and say goodbye to QoS then I would need 1 port on the switch for the VoIP phone - hence only need a 1 port router (= fancy wire?) that has DHCP - but better that my problem has a solution.

Dear Linksys,

I have purchased a BEFSR81 Router from you, but I have a problem. The summary of this problem is that the two PCs which are attached to the router, each a web server with a distinct static IP, are not seen by the outside world.

Details: I have a high speed DSL connection from XO (formerly Concentric) coming in (they told me it comes in on a Covad circuit). This signal is passed through a bridge modem, and from there it goes into the router. I have purchased four static IPs from my ISP for my own use, and two of these I have assigned to the two PCs that I have running Apache web servers (one on Win 98, the other on Win 2K Pro). In addition, I have a VoIP phone, which is a phone unit (ATA-186 made by Cisco) which plugs into the router. This unit requires DHCP. The four static IPs are I'll leave the details out on the Win 98 server on since they parallel those for the Win 2K Pro server on

My Win 2K Pro settings:
DNS 1:
DNS 2:
Physical address: ...-5A [I have obscured these entries since I don't understand the security risks in revealing it]

My Linksys BEFSR81 Router settings:
Firmware version: 2.44.2 (Dec 13, 2002)

WAN Connection Type: Static IP
DNS 1:
DNS 2:
MAC address: ...-1F

MAC address: ...-1E

DHCP Client's Table shows 1 entry:
IP Address:
MAC address: ...-E2 [= ATA MAC]
[Actually, for about 24 hours after I turn on the router, the Win 2K Pro machine also shows in this table at IP address, but then this entry goes away]

DHCP enabled: true
DHCP starting address:
Client lease time: 0
Number of DHCP users: 50
DNS 1 and 2 are as above

I have changed the Block WAN Request to Disable (this enables pinging of
Everything else is at factory settings (the three pass through settings are enabled, and the other three (Remote Management, Remote Upgrade, MTU) are disabled.

Port forwarding:
Nothing set because the IP Address must be of the form 192.168.1.something so I cannot set it to the static IPs of

Dynamic Routing:
Working Mode: Gateway
TX and RX both show Disabled

Static Routing shows three entries in the table:
Destination LAN IP / Subnet Mask / Default Gateway / Hop Count / Interface / / / 1 / WAN / / / 1 / LAN / / / 1 / LAN

Linksys technical support said that what I wanted to achieve (two externally visible, static IP PCs and a DHCP ATA-186 on the router) was possible, but too difficult to describe over the phone, so I should submit my request in writing. Please let me know how to proceed.

Perhaps another way to state my request is that it is ESSENTIAL for my servers to be visible on the web whereas I have lived without any firewall / filtering very happily for the last three years connecting through a Linksys switch. Firewall type of functionality is NOT desired if it prevents my machines from being seen at all.

I purchased the BEFSR81 because it has QoS, which may (conceivably) be important since I will have voice packets going over my network. Please don't suggest that I place an 8 port router between the phone and a switch simply for DHCP functionality as this would be a waste of both QoS and hardware.

Csaba Peter Gabor
You may also phone me at 212 586 6944 (time of day irrelevant as I would rather solve this problem than sleep).
Ron Kinner
Honored Contributor

Re: Multiple Static IPs (servers) and DHCP coexistence

Your router does NAT (Network Address Translation). This means that it expects to have a single real address on the outside (towards the Internet) and it will use multiple private addresses (192.168.1.x) on the inside.

The router does not expect multiple external IP addresses and can not handle them as you wish.

However, all may not be lost. What you can do since you don't care about the firewall and have four real addresses is to put the system back the way you had it with your two Web Server PCs plugged into a switch which is connected to a DSL Modem via Ethernet. Plug the External connection of the router into the switch. (If you don't get a Link light then you need a crossover cable.) Plug the thing that wants a DHCP into one of the the router's inside switch ports. Assign one of the remaining real IP addresses to the router's WAN interface. The problem I see is that the router may not allow you to either forward ports to a DHCP host nor put it in the DMZ so your VOIP phone may only be able to call out. If the router lets you move the to a different value then you could set it to then it could only assign one address so you would always know what IP address the DHCP device had but even if it lets you do this it is liable to stop you from doing IP forwarding to the device since it does not have a static IP.

An alternative is to take the router back or sell it to a friend. Then get a cheap LINUX box and set it up with two NICs.