Configuration problem with a bridge

[Pierre Couderc]

Under debian buster and networking.service with a basic bridge.

DHCP does not assign addresses to enp5s0 devices, but assigns them
correctly to br0 devices.

/etc/default/isc-dhcp-server :
INTERFACESv4="enp5s0 br0"


/etc/dhcp/dhcpd.conf :
subnet 192.168.16.0 netmask 255.255.255.0 {
range 192.168.16.51 192.168.16.99 ;
  authoritative;
}



/etc/networking interface :
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto enps5s0

iface enp5s0 inet manual

# The bridge :

auto br0

iface br0 inet static
         address 192.168.16.1
         netmask 255.255.255.0
         gateway 192.168.16.254
         network 192.168.16.0
         broadcast 192.168.16.255
         bridge_ports enp5s0
         bridge_stp on
         bridge_maxwait 0

iface enp5s0 inet6 auto


I have too in journalctl :

Feb 02 09:36:21 server dhcpd[874]: No subnet declaration for enp5s0 (no
IPv4 addresses).
Feb 02 09:36:21 server dhcpd[874]: ** Ignoring requests on enp5s0.  If
this is not what
Feb 02 09:36:21 server dhcpd[874]:    you want, please write a subnet
declaration
Feb 02 09:36:21 server dhcpd[874]:    in your dhcpd.conf file for the
network segment
Feb 02 09:36:21 server dhcpd[874]:    to which interface enp5s0 is
attached. **

But there is only 1 subnet for devices "inside" br0 (lxd containers) and
devices "outside".

It works fine if I install  isc-dhscp-server on another computer without
bridge, but it is not what I want to do.

What do I miss ?




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[Niall O'Reilly]

On 2 Feb 2020, at 8:55, Pierre Couderc wrote:

> INTERFACESv4="enp5s0 br0"

This is inconsistent with

> iface br0 inet static
>   ...
>   bridge_ports enp5s0

Since these two interfaces are attached to the same network segment,
only one of them belongs in the "INTERFACESv4" specification.
The one to keep is "br0", since that's the one for which you have
specified an IPv4 subnet.

I wonder whether you need "bridge_stp on". If you have just one
physical uplink ("enp5s0") and you don't have any loops in the
"inside" network, topology management with STP is superfluous.

I hope this helps.
Niall O'Reilly
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