[systemd-devel] systemd-networkd bridge with DHCP not working

Mon Mar 17 09:01:19 PDT 2014

Dear all,

*SUMMARY*

I am trying to replace dhcpcd with systemd-networkd.
Using systemd-networkd on a single physical interface works fine.
However, trying to use DHCP on a bridge fails for me.
Any help would be most appreciated.

*WORKS*

The single physical interface scenario which works:

/etc/systemd/network/50-dhcp.network contains:
--------------------------------------------------
[Match]
Name=en*
[Network]
DHCP=yes
--------------------------------------------------

"ip addr" shows:
--------------------------------------------------
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
group default
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
     inet 127.0.0.1/8 scope host lo
        valid_lft forever preferred_lft forever
     inet6 ::1/128 scope host
        valid_lft forever preferred_lft forever
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast 
state UP group default qlen 1000
     link/ether 10:bf:48:d7:68:e1 brd ff:ff:ff:ff:ff:ff
     inet 192.168.99.161/24 brd 192.168.99.255 scope global eno1
        valid_lft forever preferred_lft forever
     inet6 fe80::12bf:48ff:fed7:68e1/64 scope link
        valid_lft forever preferred_lft forever
3: enp11s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc 
pfifo_fast state DOWN group default qlen 1000
     link/ether 10:bf:48:d7:64:aa brd ff:ff:ff:ff:ff:ff
4: sit0: <NOARP> mtu 1480 qdisc noop state DOWN group default
     link/sit 0.0.0.0 brd 0.0.0.0
--------------------------------------------------

Note: I will remove lo, enp11s0, and sit0 output from further "ip addr" 
output.

So, I got an IP address and I have connectivity.

*FAILS*

Now I try to set up a simple bridge, with just one physical interface 
(eno1), trying to get the bridge to get its IP address from DHCP:

--------------------------------------------------
rm -f /etc/systemd/network/50-dhcp.network

cat > /etc/systemd/network/42-br0.netdev<<EOF
[NetDev]
Name=br0
Kind=bridge
EOF

cat > /etc/systemd/network/44-en.network<<EOF
[Match]
Name=eno1
[Network]
Bridge=br0
EOF

cat > /etc/systemd/network/46-br0.network<<EOF
[Match]
Name=br0
[Network]
DHCP=yes
EOF
--------------------------------------------------

"ip addr" shows:
--------------------------------------------------
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast 
master br0 state UP group default qlen 1000
     link/ether 10:bf:48:d7:68:e1 brd ff:ff:ff:ff:ff:ff
     inet6 fe80::12bf:48ff:fed7:68e1/64 scope link
        valid_lft forever preferred_lft forever
5: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state 
UP group default
     link/ether 10:bf:48:d7:68:e1 brd ff:ff:ff:ff:ff:ff
     inet6 fe80::78e6:aff:feca:c0ac/64 scope link
        valid_lft forever preferred_lft forever
--------------------------------------------------

I note here, that the inet6 address for eno1 matches the MAC, whereas 
the inet6 address for br0 does NOT match the MAC for br0 (which is, by 
the way, the same as the MAC for eno1).

"journalctl -b | grep DHCP" gives:
--------------------------------------------------
Mar 17 16:28:37 komplett-21 systemd-networkd[2678]: DHCP CLIENT: set MAC 
address to 7a:e6:0a:ca:c0:ac
Mar 17 16:28:37 komplett-21 systemd-networkd[2678]: br0: acquiring 
DHCPv4 lease
Mar 17 16:28:37 komplett-21 systemd-networkd[2678]: DHCP CLIENT: STARTED
Mar 17 16:28:37 komplett-21 systemd-networkd[2678]: DHCP CLIENT: DISCOVER
Mar 17 16:28:37 komplett-21 systemd-networkd[2678]: DHCP CLIENT: STOPPED
Mar 17 16:28:40 komplett-21 systemd-networkd[2678]: br0: acquiring 
DHCPv4 lease
Mar 17 16:28:40 komplett-21 systemd-networkd[2678]: DHCP CLIENT: STARTED
Mar 17 16:28:40 komplett-21 systemd-networkd[2678]: DHCP CLIENT: DISCOVER
--------------------------------------------------

followed by several combinations of:
--------------------------------------------------
Mar 17 16:28:42 komplett-21 systemd-networkd[2678]: DHCP CLIENT: 
ignoring packet: to port 9303, which is not the DHCP client port (68)
Mar 17 16:28:42 komplett-21 systemd-networkd[2678]: DHCP CLIENT: DISCOVER
Mar 17 16:29:16 komplett-21 systemd-networkd[2678]: DHCP CLIENT: 
ignoring packet: to port 138, which is not the DHCP client port (68)
--------------------------------------------------

So, I do not get an IP address from DHCP, and I do NOT have 
connectivity. But I DO receive broadcasts from the LAN (ports 9303, 138, 
etc).

I note that the systemd-networkd DHCP CLIENT says it is setting the MAC 
address to something else than what "ip addr" says the br0 IP address is 
(but the DHCP CLIENT MAC address matches the last part of the inet6 
address).

Question: Where did systemd-networkd DHCP CLIENT get this MAC address?

*SURPRISE*

Now if I run "tcpdump -i br0" or "wireshark", I see that that the DHCP 
REQUEST comes from 7a:e6:0a:ca:c0:ac.

I presume, that the problem is, that the bridge thinks its MAC is 
10:bf:48:d7:68:e1 which is the same as the MAC for eno1, but that is NOT 
the same MAC address systemd-networkd DHCP is using.

tcpdump does something to the br0 interface, so after running "tcpdump 
-i br0", I finally get an IP address for the bridge:

--------------------------------------------------
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast 
master br0 state UP group default qlen 1000
     link/ether 10:bf:48:d7:68:e1 brd ff:ff:ff:ff:ff:ff
     inet6 fe80::12bf:48ff:fed7:68e1/64 scope link
        valid_lft forever preferred_lft forever
5: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state 
UP group default
     link/ether 10:bf:48:d7:68:e1 brd ff:ff:ff:ff:ff:ff
     inet 192.168.99.175/24 brd 192.168.99.255 scope global br0
        valid_lft forever preferred_lft forever
     inet6 fe80::78e6:aff:feca:c0ac/64 scope link
        valid_lft forever preferred_lft forever
--------------------------------------------------

I would have thought that "tcpdump -i br0" would bring the interface 
into "Promiscuous mode", but neither the "ip addr" command, nor "netstat 
-i" indicates that either eno1 or br0 are in "Promiscuous mode".

*HELP*

Any help on what to put into the systemd configuration files to make the 
bridge DHCP work would be most appreciated.

FWIW: systemd is version 211 and the OS is:
http://kaarpux.kaarposoft.dk/

/Henrik