I setup bridging on my system for kvm, but on restart of the host system
(no guest VM's running) could not ping outside my local network.
Bringing the bridge down corrected the problem, but I'm trying to
understand what is going on, and how I can make networking from the VM's
work.
/etc/network/interfaces has (on the advice of a wiki page on Debian and
kvm)
auto br0
iface br0 inet dhcp
pre-up ip tuntap add dev tap0 mode tap user root
pre-up ip link set tap0 up
bridge_ports all tap0
bridge_stp off
bridge_maxwait 0
bridge_fd 0
post-down ip link set tap0 down
post-down ip tuntap del dev tap0 mode tap
My one connected interface, eth2, was brought up by hotplug with no
mention in interfaces.
Originally, with the system up, I added the br0 stanza to interfaces and
did ifup br0. This temporarily interrupted my network connections,
which was not good, but they resumed afterwords.
This time I restarted the system and found networking non-functional. I
could not ping my ISP's nameserver.
# ip route
default via 192.168.40.10 dev eth2 proto static
192.168.40.0/24 dev br0 proto kernel scope link src 192.168.40.103
192.168.40.0/24 dev eth2 proto kernel scope link src 192.168.40.102
# ifconfig
Tue Oct 1 23:14:42 PDT 2013
br0 Link encap:Ethernet HWaddr 60:a4:4c:21:bc:9f
inet addr:192.168.40.103 Bcast:192.168.40.255
Mask:255.255.255.0
inet6 addr: fe80::62a4:4cff:fe21:bc9f/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:896 errors:0 dropped:0 overruns:0 frame:0
TX packets:434 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:100681 (98.3 KiB) TX bytes:49358 (48.2 KiB)
eth1 Link encap:Ethernet HWaddr 60:a4:4c:21:bc:9f
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:17 Memory:f0600000-f0620000
eth2 Link encap:Ethernet HWaddr 60:a4:4c:21:bc:a0
inet addr:192.168.40.102 Bcast:192.168.40.255
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:990 errors:0 dropped:0 overruns:0 frame:0
TX packets:604 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:145073 (141.6 KiB) TX bytes:76668 (74.8 KiB)
Interrupt:18 Memory:f0500000-f0520000
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:16436 Metric:1
RX packets:323 errors:0 dropped:0 overruns:0 frame:0
TX packets:323 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:92559 (90.3 KiB) TX bytes:92559 (90.3 KiB)
tap0 Link encap:Ethernet HWaddr ce:45:fc:e6:32:46
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
which looked OK to me; that is, ip route seems to show external packets
should go to eth2, which is the external interface, via the .10 address
of the router. But
# ping 198.144.192.2
PING 198.144.192.2 (198.144.192.2) 56(84) bytes of data.
>From 192.168.40.102 icmp_seq=1 Destination Host Unreachable
One difference between the ifconfig above and what I saw before
rebooting was that before rebooting eth2 had no IP (which seemed odd).
ifdown br0 also brought eth2 down. I added iface eth2 inet dhcp
to /etc/network/interface and did ifup eth2; now I can reach the world
and see
# ip route
default via 192.168.40.10 dev eth2 proto static
192.168.40.0/24 dev eth2 proto kernel scope link src 192.168.40.102
The operation of bridges and taps is mysterious to me, particularly the
relation between the two, even after reviewing man pages and various
other help. I'd appreciate any guidance.
Thanks.
Ross Boylan
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