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Internal IP Lease time is buggy

Emexrulsier
4: Newbie

I have been with the service two weeks now and twice I have experienced the IP assigned to internal devices changing after a router reboot even though the lease time is set to forever.  Of course, no mac address have changed etc, just random devices will be given a brand new IP.  Very annoying when this happens to my NAS which then breaks my Plex server and FTP server and all related port forwarding rules.

1 ACCEPTED SOLUTION

Cynric
16: Advanced member
16: Advanced member

The THG3000 runs a unix variant so I'd expect it to "remember leases" in a file, e.g. dhcp.leases along the lines of linux and BSD.

https://linux.die.net/man/5/dhcpd.leases

https://www.freebsd.org/cgi/man.cgi?query=dhcpd.leases

On the other hand, the THG3000 is odd and does behave differently from every other router I've encountered 🙂

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17 REPLIES 17

Jayach
16: Advanced member
16: Advanced member

@Emexrulsier wrote:

I have been with the service two weeks now and twice I have experienced the IP assigned to internal devices changing after a router reboot even though the lease time is set to forever.


Surely that is to be expected if you reboot the router? You have rebooted the DHCP server.

Why not just set a static I.P. for those devices?

Screenshot 2021-01-09 144440.jpg

that isn't expected at all, the server ie the router should have stored the dhcp leases and not wiped them out during a reboot.

Jayach
16: Advanced member
16: Advanced member

I beg to differ, after rebooting the server will have no idea of the leases previously given. Static settings, on the other hand, will be stored in non-volatile memory and will survive rebooting.

I have never owned a router or run server from windows to linux etc that clears out all the dhcp lease cache during a reboot.  This is always a manual run option.  If a lease time for example says 24 hours, then rebooting the server would still maintain the remaining time on the lease as this would be stored in the dhcp db.  A server doesn't issue a dhcp request and then just forget about it and especially shouldn't be wiping out this cache/db on a reboot.

 

The static settings you talk about (dhcp reservations) are there to make sure on a dhcp lease request you get the same IP which should work the same as as a forever lease time (in theory), the standard leases should also be stored in ram to survive a cold boot.

Jayach
16: Advanced member
16: Advanced member

@Emexrulsier wrote:

I have never owned a router or run server from windows to linux etc that clears out all the dhcp lease cache during a reboot.  This is always a manual run option. 


Where would is save it on a router? On a server it could save it to the hard drive, a router doesn't have that option. It might be possible to save it to the non-volatile part of the memory where the firmware setting are held but why bother. It's not that important.


The static settings you talk about (dhcp reservations) are there to make sure on a dhcp lease request you get the same IP which should work the same as as a forever lease time (in theory),


Precisely, if you want your NAS etc to keep it's IP address that is where you do it. It is not what DHCP leases are for.

https://www.efficientip.com/glossary/dhcp-lease/

 


the standard leases should also be stored in ram to survive a cold boot.

RAM is volatile, it will never survive a cold boot.

/facepalm

where do you think the router stores it's running config... and this is a semi decent one, not a cheap 5 quid one from wish!

Cynric
16: Advanced member
16: Advanced member

The THG3000 runs a unix variant so I'd expect it to "remember leases" in a file, e.g. dhcp.leases along the lines of linux and BSD.

https://linux.die.net/man/5/dhcpd.leases

https://www.freebsd.org/cgi/man.cgi?query=dhcpd.leases

On the other hand, the THG3000 is odd and does behave differently from every other router I've encountered 🙂

Jayach
16: Advanced member
16: Advanced member

@Cynric wrote:

The THG3000 runs a unix variant so I'd expect it to "remember leases" in a file, e.g. dhcp.leases along the lines of linux and BSD.


And where do you think it stores that file during a reboot?

Cynric
16: Advanced member
16: Advanced member

@Jayach wrote:

@Cynric wrote:

The THG3000 runs a unix variant so I'd expect it to "remember leases" in a file, e.g. dhcp.leases along the lines of linux and BSD.


And where do you think it stores that file during a reboot?


Where? In an eMMC drive is the usual place.

I grant that there being a lack of a proper specification document for the THG3000 doesn't help us (and I have asked but got no reply from VF). However my other router "remembers" such things, so I made an assumption concerning the THG3000.