[Dnsmasq-discuss] DHCP problem when moving from one WiFi SSID to another

Chris Green cl at isbd.net
Thu Dec 27 08:45:58 GMT 2018


On Thu, Dec 27, 2018 at 08:26:25AM +0100, john doe wrote:
> On 12/26/2018 6:58 PM, Chris Green wrote:
> > I have a large[ish[ house and to provide good WiFi throughout I run
> > two Draytek routers.  The 'main' one is a Vigor 2860n which connects
> > to the internet by FTTC, the second one is an old Vigor 2820n which
> > has its WAN disabled and the LAN hardwired to the 2860n LAN.
> > 
> > Currently I'm using the same SSID on both routers, I've read quite a
> > lot around this and the weight of opinion seems to be that using the
> > same SSID should work OK and is more transparent to the user than
> > using different ones.  However I have also tried different SSIDs for
> > the two routers requiring user intervention to move from one to the
> > other, this shows the same symptoms (described below) as using the
> > same SSID.
> > 
> > What happens is that when I move around such that the WiFi connection
> > should move from the 2820n to the 2860n my laptop loses its IP
> > address.
> > 
> > DHCP and DNS is provided by dnsmasq running on a RaspberryPi, the
> > basic IPV4 setup is as follows:-
> > 
> >     Vigor 2860n - 192.168.1.1
> >     Raspberry Pi - 192.168.1.2 (runs dnsmasq)
> >     Desktop 192.168.1.3
> >     Vigor 2820n - 192.168.1.20
> > 
> > The Pi assigns IP addresses from 192.168.80 to 192.168.1.127 and the
> > conf file is:-
> > 
> >     domain-needed
> >     bogus-priv
> >     expand-hosts
> >     domain=zbmc.eu
> >     dhcp-range=192.168.1.80,192.168.1.127,12h
> >     dhcp-option=3,192.168.1.1
> >     local=/zbmc.eu/
> >     cname=bbb,beaglebone
> >     cname=mx201,maxine-X201
> >     cname=ben,DESKTOP-978VD5M
> >     cname=oki,MC342-AE529C
> >     dhcp-host=00:BB:3A:E9:A3:15,maxineKindle
> >     dhcp-host=00:09:B0:C9:CE:81,onkyoTx-nr616
> >     dhcp-host=28:EF:01:2D:EB:07,chrisKindle
> >     dhcp-host=08:EB:74:9D:47:53,humaxFreeview
> >     dhcp-host=2C:08:8C:CC:9A:9E,humaxYouview
> >     dhcp-host=00:1F:E2:4E:8F:CA,maxineStudy
> >     dhcp-host=00:25:36:AE:52:9C,192.168.1.50
> > 
> > 
> > My laptop seems to lose its IP address whenever I move from one
> > Draytek's WiFi to the other but only when the IP is assigned by
> > dnsmasq.  If I connect to my guest network (192.168.6.x) then I get a
> > IP address assigned by the 2860n and a good connection to the outside
> > world.  If I then reconnect to the 'local' WiFi the laptop loses its
> > IP address.  It's as if dnsmasq doesn't see the disconnection and
> > doesn't answer the new DHCP broadcast from my laptop.  If I leave it
> > disconnected for a minute or two and then re-connect to the WiFi it
> > *does* get an IP.
> > 
> > 
> > Can anyone explain what might be wrong and/or a fix or workaround?
> > 
> > 
> 
> How is this issue different from the one you posted a fiew mounths back (1)?
> 
> Did you try what Simon Kellie suggested then?
> 
> 1)
> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2018q2/012225.html
> 

He didn't really.  :-)   He said:-

"but I don't have any concrete suggestions on how to fix it. I think the SSID change
is a red-herring."

But, yes, it is basically the same issue, but now I'm not changing SSID.

I have now changed the dnsmasq configuration to set
dhcp-authoritative, maybe that will do something.

-- 
Chris Green



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