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Other broadband queries

DHCP Reservation Not Being Honoured

4: Newbie



I have a HHG2500 router and for around 4 months now, I'm having issues with the router honouring the entries I've set in the DHCP Reservation table. Before this, it was working fine.


Every few days, some of the devices in the reservation table are assigned new IP addresses and this is extremely problematic for me for various reasons which I won't go in to here.


I've tried a factory reset but it still happens.


I've been on to the chat with Vodafone three times now trying various things and I have to say, it's been extremely frustrating and it's very evident that the agents I've spoken to have very limited technical knowledge around DHCP reservation and how it works and often conflate DHCP with DNS. I know the average home broadband user wouldn't have a clue what DHCP reservation is and would never need to use it so may be this plays a part in the lack of knowledge.


In my opinion, it sounds like I need a replacement router but they seem to be extremely reluctant to arrange that for some reason.


I can't really see what else I can try that I haven't already to get this to work like it used to.


I am running the latest firmware on the router. 


Anyone able to offer any advice or how else I can get Vodafone to replace the router?



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16: Advanced member

DHCP is run as a service, so it's unlikely that what you are seeing is any kind of component failure, and in an identical environment with the same router with the same firmware you'd have to expect an identical failure to take place - so a replacement router is unlikely to solve this!


I'm going from memory here, but I believe on the HHG2500 you can only make DHCP reservations outside of the pool of available addresses (other routers often work a little differently).  So I'm wondering if you could have another device which is grabbing what is supposed to be a reserved IP and using it as a static IP (not allocated by the DHCP server.  I'm wondering if you'd have the ability to set the addresses on your devices as static and addressed to those same local IPs as you have reserved. *fully aware this does not always work, especially with security-related devices!

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4: Newbie

I don't that's quite correct around only being able to reserve outside the pool of addresses for two reasons.


1) As mentioned, it's been working fine for 12 months.


2) I have 10 DHCP reservations all within the IP Pool and anecdotally, 60% of them appear to be working fine at any one time and random devices will have new IP's assigned periodically.


Your second point also cannot be valid because if I look at both the NAT table and verify by running a local network scanner, the reserved IP's are actually free and available but DHCP has assigned a new IP to the device for some reason.

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4: Newbie

Here's some more info that I've found this morning which further leads me to believe it's a router software issue.


Device named 'computer-1' in DHCP still has the correct IP assigned to it and is the one reserved in DHCP. If I ping computer-1.broadband, it works fine and I get a response so no issues here.


However, if we take 'computer-2' as an example. It also has a DHCP reservation but DHCP has assigned it a new IP address and not the one in the reservation table. If I now ping computer-2.broadband, the hostname cannot be resolved to an IP address even though there is a valid entry in the NAT table with computer-2 along with the new IP address that DHCP has assigned. To highlight, it's not that there is no response from the ping but that the hostname cannot be resolved. I can replicate this behaviour across multiple devices where entries exist in the DHCP Reservation table. In my mind, this can only be cause by something going awry with DHCP.

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7: Helper

I have the THG3000 router so can't comment directly on the earlier router, but have to say I don't think it is likely to be a hardware fault.

Personally I have set the devices I want to have a fixed I.P. to outside of the pool in in the static list but then fix it in the devices themselves. Mind you I only have 2 such devices, so no problem.

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