On 14/05/18 18:50, Chris Green wrote:
> I have a large house and run two Draytek Vigor routers to provide full
> coverage. The 'main' router is a Draytek 2860n which has the VDSL
> connection to the internet. The second router is a Draytek Vigoer
> 2820n which has no WAN connections and just has its LAN connected to
> the 2860n's LAN side.
> DHCP/DNS is provided by a Raspberry Pi running dnsmasq.  Everything is
> otherwise pretty standard, 192.168.1.x private network with the 2860n
> at and the Pi at
> I have the routers' WiFi set up so they have different SSIDs. In
> general it all works fine, I can connect my laptop to either SSID as
> required.
> The problem I have is when I move around the house. My laptop runs
> xubuntu 17.10 and uses Network Manager to handle the networking. So,
> say I'm connected to 2820n and move to the other side of the house
> where I need to connect to 2860n. I manually use the Network Manager
> applet to disconnect from 2820n and connect to 2860n. It appears to
> work fine and says I'm connected but most times that I do this the
> DHCP set-up fails. I have a connection but there is no default route
> and no DNS and the laptop has no IP address assigned (all IPV4 this).
> Sometimes it works OK and usually if I disconnect and wait a while
> (say a minute or two) and then reconnect it will work OK.
> It seems as if dhclient is failing as if I run it manually when in the
> not working state it just hangs.  Does dnsmasq have some sort of delay
> before 'dropping' a DHCP client?  I.e. is it possible that dnsmasq
> sees the same MAC address re-connecting and assumes that it still has
> its IP setup?  If so is there some way I can make dnsmasq quicker at
> seeing that a client has disconnected?

This looks more like a layer-2 problem than a DHCP/IP one. There's one
IP network, so the host should just be able to continue with the
existing DHCP lease.

To work, though, it does require that the layer-2 ethernet switches note
that the topology of the network has changed, and that the packets to
the MAC address in question have to go over different network ports. I
suspect that the couple of minutes delay is timeout on that, but I don't
have any concrete suggestions on how to fix it. I think the SSID change
is a red-herring.



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