Extending Ethernet over 1000'

[Markap]

Hello, I'm trying to solve a particular problem. How to extend "ethernet" over 1000 feet between devices. Here's the scenario. Envision a triangle with point 'a' at the top. Here we have a router with network egress to the Internet. On the lower left is point 'b' with a hub and same on the lower right, point 'c'. a - b is 1000 feet as is a - c. (b to c doesn't matter, not interconnected).

I tried using Xpeed SDSL modems in their back-to-back bridge configuration with parital success. The link is established and for a short time all works ok.

The problem is: When a user arrives on the hub at point b and requests IP address (DHCP), all is ok. BUT, if this same user then moves to point c and tries to get an ip address, one is never returned.

Putting a packet sniffer on the line shows the DHCP request being transmitted bact to the router at point a but the responses never get back to the user who is now over at point c.

It seems like the Xpeeds make an association between the users MAC address and location so when the same MAC shows at the second point, the Xpeed redirects the DHCP response back to the original location and never passes it back to the user at this new location.

Anyone know how to:
1. fix the above scenario with either different settings on the Xpeeds or by inserting a new device
or,
2. recommend another means of establishing long ethernet runs which will avoid this MAC/DHCP issue?

Thanks!!

 

[jimbopalmer]

two comments;

many fiber ethernet standards allow 2 kilometers or more

setting the DHCP address renewal time shorter at the server may be a part of the solution. Or setting the ARP timeout shorter in the Xpeed modems I tried to remain child-like, all I acheived was childish.

 

[Markap]

Thanks for the info. Can't use fiber because I'm also running power (-48vdc) over the twisted pair so I can line power the far end Xpeed and additional equipment. The DHCP issue doesn't seem to be server related - I'll look for an ARP setting on the Xpeeds.

 

[audiopimp]

I would and have gone the fiber way in tyhe past , these would probablty be your best solution if the costs permit. Do some research, present the pros and cons to yourpurchasers or boss and your off!!

 

[juggy]

Can we have some more info please .. A is the site that holds the DHCP Server.. and is connected via a hub/switch to B? If so DHCP works fine like you say above. C runs two devices that allow you to bridge a connection between a and c. These two devices seem to work fine. Please provide some more info on the above if wrong and below. Does a new pc on site c get a DHCP addres with no problem? If so thats encouraging. If when you move one PC from B to C before they do this or more likey you do this issue a IPconfig /release to remove the address hopefully from DHCP. If this works then move it over. If this does not pick up an address then your snookered. Ive had this problem with an IBM bridge it just wouldnt pick up a DHCP address and logically I couldnt see a reason for it. Now if money grew on trees Id dump your two bridge devices and get someone in to install some fibre for you and then buy two cheap fibre to cooper convertors if poss and hub so the setup looks more 'networked'. If you dont have this luxuary then you could always get a battered old box and install NT on it and install a DHCP relay agent on it. This will pass over the DHCP request hopefully. If any routing is in play then ignore the above.. and please readivse. Bridges keep a table of MAC addresses that pass through them so they can make intelligent decisions about traffic flow so if a mac adrss comes in on port a and always goes to port b after a time traffic will always be forwarded to port b. If you move it then it should still work but if you see anything like clear bridge table or mac table or clear cam table then do this after the move it may also help.