[Dnsmasq-discuss] No DHCP leases handed on bridge interface

[Sébastien Delafond]

On 2016-07-15, Albert ARIBAUD <albert.aribaud at free.fr> wrote:
> That leads to further questions, at least. VLANs do not cause
> problems for dnsmasq, but bridging VLANs may be tricky and more
> prone to network misconfigurations.
>
> So just to make sure, can you list all interfaces and all bridges in
> your system, including ifconfig outputs?

Sure:

  $ brctl show
  bridge name     bridge id               STP enabled     interfaces
  br.eth0-2               8000.1cb72c761568       no              eth0.2
  $ ifconfig
  br.eth0-2 Link encap:Ethernet  HWaddr 1c:b7:2c:76:15:68  
	    inet addr:192.168.1.1  Bcast:192.168.255.255  Mask:255.255.0.0
	    UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
	    RX packets:872 errors:0 dropped:0 overruns:0 frame:0
	    TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
	    collisions:0 txqueuelen:1000 
	    RX bytes:130641 (127.5 KiB)  TX bytes:258 (258.0 B)

  eth0      Link encap:Ethernet  HWaddr 1c:b7:2c:76:15:68  
	    UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
	    RX packets:140624 errors:0 dropped:0 overruns:0 frame:0
	    TX packets:103007 errors:0 dropped:0 overruns:0 carrier:0
	    collisions:0 txqueuelen:1000 
	    RX bytes:91383944 (87.1 MiB)  TX bytes:74433059 (70.9 MiB)
	    Interrupt:180 Base address:0x5000 

  eth0.1    Link encap:Ethernet  HWaddr 1c:b7:2c:76:15:68  
	    inet addr:172.16.25.234  Bcast:172.16.25.255  Mask:255.255.255.0
	    UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
	    RX packets:748 errors:0 dropped:0 overruns:0 frame:0
	    TX packets:355 errors:0 dropped:0 overruns:0 carrier:0
	    collisions:0 txqueuelen:1000 
	    RX bytes:51266 (50.0 KiB)  TX bytes:41482 (40.5 KiB)

  eth0.2    Link encap:Ethernet  HWaddr 1c:b7:2c:76:15:68  
	    UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
	    RX packets:4 errors:0 dropped:0 overruns:0 frame:0
	    TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
	    collisions:0 txqueuelen:1000 
	    RX bytes:1312 (1.2 KiB)  TX bytes:258 (258.0 B)

  lo        Link encap:Local Loopback  
	    inet addr:127.0.0.1  Mask:255.0.0.0
	    inet6 addr: ::1/128 Scope:Host
	    UP LOOPBACK RUNNING  MTU:65536  Metric:1
	    RX packets:285419 errors:0 dropped:0 overruns:0 frame:0
	    TX packets:285419 errors:0 dropped:0 overruns:0 carrier:0
	    collisions:0 txqueuelen:0 
	    RX bytes:77987874 (74.3 MiB)  TX bytes:77987874 (74.3 MiB)

So, only one bridge (that's not bridging much right now since it only
contains eth0.2).

> FYI and assuming you can read French :)

I most definitely can, heh :)

> here is an overview of an issue I had with bridged VLANs:
> <http://albert.aribaud.net/fr/node/11>.
> 
> The Englih TL;DR of it is: I had eth0 and eth1 bridged (as "br0") and
> needed VLAN 100 traffic to pass across transparently. Not only did I
> need to also bridge eth0.100 and eth1.100 (as "br100"), but I also had
> to use iptables to make br0 reject VLAN 100 packets, otherwise they
> were dropped instead of being processed and passed across by br100.
> 
> Again: no reason why your problem might be the one I had; I'm just
> giving an example of how mixing bridges and VLANs can be tricky.

Interesting issue, but it doesn't feel like what I'm facing right now:
the fact that ISC dhcpd serves leases OK seems to indicate that the
network configuration itself is all right.

Plus, there really is not VLAN at all outside of that
software-programmable NIC anyway: tcpdump -e confirms that packets
going in and out (either on br0.eth-2 or eth0.2) are not tagged. I've
tested that by assigning a manual IP to my client and initiating a
telnet connection to the outside.

Does this make any sort of sense ? :)

Cheers,

--Seb