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Old 06-04-2023, 02:46 PM   #1
Chewbakka
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Registered: Dec 2004
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Qemu/KVM Bridging

Hello,
I have a host machine running a FreeBSD vm, which i need to provide with Internet connectivity.

I tried the following:
On my host machine i created a bridged ip link add bridge0 type bridge, secondly i created a tap interface to be used by the vm. ip tuntap add tap0 type tap, next i associated the tap device with the bridge interface: ip link set tap0 master bridge0. The vm is given an address in the bridged network 172.16.10.0/24.

When launching the vm, i give the following parameters to qemu "-netdev tap,id=net1,ifname=tap0 -device virtio-net-pci,netdev=net1"

Next i added iptables rules to the host machine:
iptables -t nat -A POSTROUTING -s 172.16.10.0/24 -o eno1 -j MASQUERADE where eno1 is the host machines interface.

Enable routing:
sysctl -w net.ipv4.ip_forward=1

#Allow traffic and related/established connections on the Forwarding chain:
iptables -A FORWARD -i bridge0 -o eno1 -j ACCEPT
iptables -A FORWARD -s 172.16.10.0/24 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

The vm is able to ping the host machines bridge0 on 172.16.10.100, but no Internet connectivity.
Any idea what i am missing here?
 
Old 06-06-2023, 08:41 AM   #2
jefro
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Where did you get this example to use?

https://wiki.qemu.org/Documentation/Networking#Tap

Make it easier maybe by starting with -nic tap??
 
Old 06-06-2023, 12:59 PM   #3
jayjwa
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What's the routing table look like?

Code:
ip -c route show
default via 74.x.x.1 dev eth0 proto dhcp src 74.x.x.131 metric 1002 
74.x.x.0/19 dev eth0 proto dhcp scope link src 74.x.x.131 metric 1002 
127.0.0.0/8 dev lo scope link 
192.168.20.0/24 dev br0 proto kernel scope link src 192.168.20.1
Code:
ip link add name br0 type bridge
ip link set br0 type bridge stp_state 1
ip tuntap add dev tap0 mode tap
ip link set dev tap0 master br0
I usually forward everything, net.ipv4.conf.all.forwarding = 1, and run a DHCP server servicing br0.
Code:
INTERNAL_NETWORK="192.168.20.0/24"
iptables -t nat -A POSTROUTING -m comment --comment "Masquerading LAN rfc1918 addresses" -s $INTERNAL_NETWORK -j MASQUERADE
Code:
qemu-system-i386 -m 512m -cdrom windows_me_115_oem_full.iso -cpu pentium3 -boot order=c,menu=on -rtc base=localtime -device pci-serial-4x -vga cirrus -device ich9-intel-hda -device hda-output,audiodev=snd0 -device AC97,audiodev=snd0 -audiodev pa,id=snd0  -device pcnet,netdev=net0,mac=52:54:00:12:34:57 -netdev tap,ifname=tap7,id=net0,script=no,downscript=no -hda c_harddisk_me_sf.img -serial pty -daemonize
Note Qemu syntax has changed radically over the years. This is 8.0.2.

taps6-8 aren't in use right now.
Code:
ip -c link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 6c:4b:90:17:7c:1d brd ff:ff:ff:ff:ff:ff
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 60:14:b3:6f:a3:bf brd ff:ff:ff:ff:ff:ff
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
    link/ether aa:00:04:00:01:04 brd ff:ff:ff:ff:ff:ff
5: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 42:b6:75:ba:10:d3 brd ff:ff:ff:ff:ff:ff
6: tap1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 4a:80:2e:b0:c6:06 brd ff:ff:ff:ff:ff:ff
7: tap2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 3e:fd:17:41:5f:e7 brd ff:ff:ff:ff:ff:ff
8: tap3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 6a:a9:5a:71:f1:84 brd ff:ff:ff:ff:ff:ff
9: tap4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether e2:69:d1:cf:8c:7e brd ff:ff:ff:ff:ff:ff
10: tap5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT group default qlen 1000
    link/ether 2a:c6:57:e1:10:03 brd ff:ff:ff:ff:ff:ff
11: tap6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast master br0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 6a:14:62:8f:d9:40 brd ff:ff:ff:ff:ff:ff
12: tap7: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast master br0 state DOWN mode DEFAULT group default qlen 1000
    link/ether c6:d4:7f:06:9d:af brd ff:ff:ff:ff:ff:ff
13: tap8: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast master br0 state DOWN mode DEFAULT group default qlen 1000
    link/ether b6:38:5f:33:11:62 brd ff:ff:ff:ff:ff:ff
 
Old 06-06-2023, 03:02 PM   #4
Chewbakka
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Registered: Dec 2004
Posts: 5

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So i figured out the issue ...
The problem was that i had nftables running concurrently with iptables and update-alternatives pointed to nft..sigh.
Anyways i appreciate the help
 
  


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