[Dnsmasq-discuss] Dnsmasq fails to offer static lease (IPv4) occasionally

Timo Sigurdsson public_timo.s at silentcreek.de
Mon Jan 11 16:11:42 GMT 2016


Sorry, forgot to mention the dnsmasq version is 2.73 (dnsmasq-full 2.73-1) on OpenWrt Chaos Calmer 15.05.
Let me know if I can provide other useful information.

Regards,

Timo

Timo Sigurdsson schrieb am 11.01.2016 15:44:

> Hi,
> 
> I'm using dnsmasq on OpenWrt as my DHCP and DNS server for my home network. I
> set
> up static leases for all my clients which mostly works well, but sometimes
> dnsmasq fails to offer the static IPv4 lease to some of my clients. Instead,
> they
> will get a dynamic IP. Now this doesn't happen too often (sometimes it works
> for
> 2 weeks without any issue), but it does happen occasionally (sometimes even
> with 2 clients on the
> same day).
> 
> Some basic information:
> - I first used the OpenWrt configuration interface UCI to set up the static
> leases. But after I became aware of the occasional dynamic assignments, I
> switched to configuring the static leases via /etc/hosts and /etc/ethers
> instead.
> But that didn't solve it.
> 
> - I have a total of 16 static leases defined which covers all my network
> devices.
> I only use static leases for IPv4. The IP range dnsmasq can use is big enough
> (100 addresses) and all static leases are within that range, of course.
> 
> - The clients with which I saw this problem don't have much in common. One is a
> wired desktop computer running Windows 7. The other is a wireless MacBook Air
> running OS X. The only similarity I find is that these are both clients that
> are
> not running 24/7. They are often shut down and also often go to standby and
> wake
> up from it. I have two servers on the network that are always connected and
> with
> them I haven't observed any false IP assignment yet.
> 
> - All clients have only one way to connect to the network. So, there are no
> laptops that would sometimes connect wireless and sometimes wired or anything
> like that.
> 
> - I tried different lease times from 2h to 12h with no effect so far.
> 
> - Before I started using OpenWrt with dnsmasq, I used a Linksys Router with the
> proprietary vendor firmware and had set up the same static leases there, too. I
> never observed such an issue with any of these (same) clients, so it shouldn't
> be caused by the clients themselves.
> 
> When a client does not receive the correct static lease, I can see in the logs
> that dnsmasq doesn't send a DHCPOFFER after a DHCPDISCOVER. But I don't see
> why.
> I can see, though, that when a client gets a dynamic IP instead of a static
> one,
> dnsmasq refuses to assign the local domain name (hostname.lan) to this client
> that is listed in /etc/hosts. So, dnsmasq seems to recognize the client after
> all, but fails to offer the static lease. Since I have only seem this problem
> so
> far with clients that often disconnect and reconnect or go to standby and wake
> up
> again, I just assume that it might have to do something with DHCP leases that
> haven't expired yet. That's why I tried diffent lease times but so far with no
> luck. Another thing I noticed is: When a client get's a dynamic lease and asks
> for renewal of the lease at some point, dnsmasq will just acknowledge this
> request rather than assigning the static lease to the client. So unless I force
> the client to reconnect (and sometimes reboot the router), they will just keep
> using the dynamic lease.
> 
> What ca I do to prevent this from happening? How can I ensure clients will be
> served the correct static lease?
> In addition, what is a good or recommended lease time for a home network where
> clients should keep the same IP address and where there is a mix of wired and
> wireless clients?
> 
> I had asked this on the OpenWrt forums before, but nobody was able to help me
> there. So, I'd really appreciate any insights or hints you might have. Thanks.
> 
> Regards,
> 
> Timo
> 
> 
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