i have a problem with a network , there is total 40 computers in my LAN network two tplink ethernet switches and have a broa

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lbvr

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May 16, 2015
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i have a problem with a network , there is total 40 computers in my LAN network two tplink ethernet switches and have a broadband connection . computers connected with first Switch do working correctly (internet connection) . but the computers connected with second Switch dont working (i have tried troubleshoot .the feedback message: Local area connection not have a valid IP configuration ) modem has enable DHCP , no static ip given to the PCs . another 20 Pcs are working properly at the same time. i been set up the hole network from the first (the switches i have made connection between them from port 24(switch 1) to port 24 (switch 2) ) , i hope tomshardware experts could help me .
i am using level 2 tplink tl sg2224web 24 ports switch and yes the modem doing the job as DHCP server
 
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Is the modem that acts as the dhcp server connected to the first switch of which the computers are working?

Also, you have not mentioned what switches you use. Are you using one of the level 3 switches?

What I am thinking here. If all systems on one switch work and all systems on the other are not working by having an IP problem, then I expect something wrong with the switch (configuration). Although I have never handled them myself, level 3 switches have router functionality and DHCP packets do not travel between networks, meaning a level 3 switch can potentially block dhcp packets. They usually have dhcp relay options, but they can be disabled.

Also, some level 3 switches also have potential dhcp servers included with them.

Could...
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bill001g

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Aug 9, 2012
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Switches are pretty stupid...assuming you are using unmanged ones. The only thing I can think of is that the connection between the switches is not active. Older switches that could only go 10/100 you used to need a cross over cable. New stuff and all gig switches you can use normal straight cables. You should be able to tell if there are lights on.

It could be something strange like the DHCP pool is too small but then you would think the working machines would be spread over both switches.

Maybe plug the router directly into the second switch and see if then those machine then work and the ones on the other machine do not.
 
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bleijendeckers

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Sep 14, 2013
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Is the modem that acts as the dhcp server connected to the first switch of which the computers are working?

Also, you have not mentioned what switches you use. Are you using one of the level 3 switches?

What I am thinking here. If all systems on one switch work and all systems on the other are not working by having an IP problem, then I expect something wrong with the switch (configuration). Although I have never handled them myself, level 3 switches have router functionality and DHCP packets do not travel between networks, meaning a level 3 switch can potentially block dhcp packets. They usually have dhcp relay options, but they can be disabled.

Also, some level 3 switches also have potential dhcp servers included with them.

Could you look what the IP of one of the computers on switch 1 is and what the ip of one of the computers of switch 2 is?
 
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bleijendeckers

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Sep 14, 2013
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Actually, bill001g's suggestion is much more probable then what I am suggesting.

If you check the IP addresses on the non functioning computers and they appear to be in the range 69.254.0.1 t/m 169.254.255.254 (apipa range) and you haven't got a lvl 3 switch then it probably is the cabling. Anyways, if it is in that ip range the pc's cannot reach the dhcp server and you can assume packets on that switch are not reaching systems on the other switch.
 
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lbvr

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May 16, 2015
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