I run a Ubuntu machine which hosts via libvirt several guest VMs (also Ubuntu). The guests can access the Internet, while the host can only reach the local network, including the gateway. This seems weird and I have no clue as to what may be the root cause.
I cannot recall where along the line this problem occurred first or which change triggered it. So I just describe the current situation in terms of some config and output:
$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 a.b.c.1 0.0.0.0 UG 0 0 0 eth0
a.b.c.0 0.0.0.0 255.255.255.0 U 0 0 0 br0
a.b.c.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 br0
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
This seems to say basically the same:
$ ip route show
default via a.b.c.1 dev eth0 proto static
a.b.c.0/24 dev br0 scope link
a.b.c.0/24 dev eth0 proto kernel scope link src a.b.c.38 metric 1
169.254.0.0/16 dev br0 scope link metric 1000
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1
/etc/network/interfaces :
auto lo
iface lo inet loopback
auto br0
iface br0 inet static
address a.b.c.38
netmask 255.255.255.0
network a.b.c.0
broadcast a.b.c.255
gateway a.b.c.1
dns-nameserver XXX.XXX.XXX.XXX XXX.XXX.XXX.XXX XXX.XXX.XXX.XXX
bridge_ports all
bridge_stp yes
bridge_fd 0
post-up /sbin/ethtool -s eth0 wol g
post-down /sbin/ethtool -s eth0 wol g
This command fails:
$ sudo ifdown eth0 && sudo ifup eth0
ifdown: interface eth0 not configured
Ignoring unknown interface eth0=eth0.
Another command concerning the bridge:
$ brctl show
bridge name bridge id STP enabled interfaces
br0 8000.14dae9726e93 no eth0
vnet0
vnet1
vnet2
virbr0 8000.000000000000 yes
This seems suspicious:
$ arp -n
Address HWtype HWaddress Flags Mask Iface
a.b.c.50 (incomplete) eth0
a.b.c.63 (incomplete) eth0
a.b.c.1 ether 00:00:0c:07:ac:3d C br0
a.b.c.63 ether 4c:72:b9:8f:b8:6c C br0
a.b.c.50 (incomplete) br0
a.b.c.40 ether 52:54:00:2f:79:ac C br0
a.b.c.39 ether 00:25:90:7c:f8:94 C br0
a.b.c.1 (incomplete) eth0
a.b.c.48 ether 3c:07:54:13:7c:55 C br0
a.b.c.2 ether f0:f7:55:2a:15:00 C br0