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Author Topic: DHCP IP Conflicts with DIR-827  (Read 7550 times)

vfontjr

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DHCP IP Conflicts with DIR-827
« on: January 18, 2012, 07:46:21 AM »

I have two DIR-827 routers. One is the primary router attached to the WAN, the second is serving as an AP in my office. The AP has DHCP turned off.

Several times now, I've had IP conflicts where two computers on my network received the same IP address from the DHCP server. The difference between the two computers is that one is operating at 5Ghz, the other at 2.4Ghz. These two are always the ones that collide in conflict. I believe this is a bug in the DIR-827 firmware.

The workaround I use is to reserve IP addresses for my computers using the router's DHCP reserve function. This way, they always receive the same IP address.
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FurryNutz

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Re: DHCP IP Conflicts with DIR-827
« Reply #1 on: January 18, 2012, 08:12:19 AM »

It's always preferred to setup DHCP reserved IP addresses for all devices ON the router. Setup/Networking

Ensure devices are set to auto obtain an IP address.
What Firmware version is currently loaded? Found on routers web page under status.


Some things to try:
Ensure DNS IP addresses are being filled in under Setup/Internet/Manual? You can find these under Status/Device Info/Wan section.
Turn off Advanced DNS Services if you have this option under Setup/Internet/Manual.
Turn on DNS Relay under Setup/Networking.
Set Firewall settings to Endpoint Independent for TCP and UDP.
Enable uPnP and Multi-cast Streaming under Advanced/Networking.
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Cable:200mb/10Mb>NetGear C7800>DIR-882>DGS-1100>HP 24pt Gb Switch. COVR-3902/2202/1203,DIR-2680,890L,882,880L,868L,DNR-202L,DNS-345x2,DCS-933L,936L and 960L.
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AquaManiac

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Re: DHCP IP Conflicts with DIR-827
« Reply #2 on: January 18, 2012, 08:20:06 AM »

Interesting. Can you elaborate on the operating systems used for those two computers and perhaps the dhcp lease assignment details for each. What is the time interval between the two computer uses? FYI, dhcp clients typically issue a renewal at half-life of dhcp lease. Also, dhcp clients upon boot-up, typically request their current dhcp ip (what they had at their last shutdown) as part of their discovery request to the original dhcp server.

My thoughts at this time to potentially explain the dhcp ip conflicts with these two existing LAN clients is that maybe the dhcp interval lease time has been exceeded on the dhcp server and when the offline clients startup they use their out-of-date lease(s) before acquiring a new one from the router's internal dhcp server.

Another thought that could cause this issue is the rebooting of the router which would cause it to not retain its previous dynamic leases it handed out to local clients. So, if client A received 192.168.0.100 as a dynamic lease from the router at a point in time. Then, router was reset somehow before client A renewed its lease, the router could assign out the beginning of its fresh client dhcp pool to client B having the same 192.168.0.100. Most dhcp servers will attempt to ping a lease before assigning one out to help avoid ip conflicts with pre-existing or rouge clients. If firewall rules or equivalent on the local client(s) prevent the dhcp server's preventive ping check then the dhcp server could easily hand out conflicting ips.
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vfontjr

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Re: DHCP IP Conflicts with DIR-827
« Reply #3 on: January 26, 2012, 01:15:19 PM »

The two computers that appear to be conflicting are both Windows 7. One has a dual band radio but connects only to the 5Mhz band. The other one only has a 2.4Mhz radio.We also have a MacBook Pro that was conflicting at times. The MacBook also has a dual band that is setup up with 5Mhz as the preferred connection.

I could not see a pattern as to why this was occuring, but since I've reserved all the IP addresses, everything has been working flawlessly.
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FurryNutz

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Re: DHCP IP Conflicts with DIR-827
« Reply #4 on: January 26, 2012, 01:20:06 PM »

Were you setting a static IP address on the devices or are they reserved now on the router? Router is preferred to reserve IP address and set devices to auto obtain.
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Cable:200mb/10Mb>NetGear C7800>DIR-882>DGS-1100>HP 24pt Gb Switch. COVR-3902/2202/1203,DIR-2680,890L,882,880L,868L,DNR-202L,DNS-345x2,DCS-933L,936L and 960L.
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vfontjr

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Re: DHCP IP Conflicts with DIR-827
« Reply #5 on: February 05, 2012, 06:17:53 PM »

I never use static IP addresses because I travel alot and use hotel and airport internet connections. I have the IP addresses reserved on my router now.
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Cobra

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Re: DHCP IP Conflicts with DIR-827
« Reply #6 on: February 05, 2012, 08:31:03 PM »

I never use static IP addresses because I travel alot and use hotel and airport internet connections. I have the IP addresses reserved on my router now.

Reserved addresses means the devices always get the same IP from the router which makes the addresses static.
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FurryNutz

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Re: DHCP IP Conflicts with DIR-827
« Reply #7 on: February 05, 2012, 09:25:14 PM »

It's ok if you reserve them ON the router, just means while your home and not traveling, you get the same IP address from the router. If you leave the device set up for Auto Obtain, you'll be ok when you travel as it will get an IP address when it connects to where ever your at.
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Cable:200mb/10Mb>NetGear C7800>DIR-882>DGS-1100>HP 24pt Gb Switch. COVR-3902/2202/1203,DIR-2680,890L,882,880L,868L,DNR-202L,DNS-345x2,DCS-933L,936L and 960L.
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