KVM guest can't access internet
12,644
I received a comment on Reddit that pointed me in the right direction with this one: https://www.reddit.com/r/linuxadmin/comments/bdy6sz/kvm_guest_cant_access_internet/
The problem is that Docker changes the default policy for the FORWARD chain in iptables to DROP.
A rule to allow traffic has to be added. Running this command added the required rule and fixed the issue:
sudo iptables -I FORWARD -i br0 -o br0 -j ACCEPT
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Author by
colincameron
iOS and OS X developer who wonders into C# and PHP occasionally.
Updated on September 18, 2022Comments
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colincameron over 1 year
I have a number of Ubuntu guests running on an Ubuntu 16.04.6 kvm host.
Since I had to reboot my host, networking no longer works correctly. The host and guest can access each other, but my guest can't access the internet, and I can't access the guest from any other computers on the network. The host had Docker installed pre-reboot (may be relevant).
Using one guest as an example: Ubuntu 16.04.4
- Host IP: 10.0.10.2
- Guest IP: 10.0.10.13
- Guest KVM network settings:
- Network source: Bridge br0: Host device eno1
- Device model: virtio
Ping results:
colin@host:~$ ping 10.0.10.13 PING 10.0.10.13 (10.0.10.13) 56(84) bytes of data. 64 bytes from 10.0.10.13: icmp_seq=1 ttl=64 time=0.207 mscolin@host:~$ ping 1.1.1.1 PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data. 64 bytes from 1.1.1.1: icmp_seq=1 ttl=58 time=119 mscolin@guest:~$ ping 10.0.10.2 PING 10.0.10.2 (10.0.10.2) 56(84) bytes of data. 64 bytes from 10.0.10.2: icmp_seq=1 ttl=64 time=0.257 mscolin@guest:~$ ping 1.1.1.1 PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data. --- 1.1.1.1 ping statistics --- 9 packets transmitted, 0 received, 100% packet loss, time 7999msRunning tcpdump on host during tests (pinging host>guest, guest>world, guest>host) showing no reply:
colin@host:~$ sudo tcpdump -nni br0 icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on br0, link-type EN10MB (Ethernet), capture size 262144 bytes 15:57:52.684722 IP 10.0.10.2 > 10.0.10.13: ICMP echo request, id 29324, seq 1, length 64 15:57:52.684953 IP 10.0.10.13 > 10.0.10.2: ICMP echo reply, id 29324, seq 1, length 64 15:57:53.683713 IP 10.0.10.2 > 10.0.10.13: ICMP echo request, id 29324, seq 2, length 64 15:57:53.683891 IP 10.0.10.13 > 10.0.10.2: ICMP echo reply, id 29324, seq 2, length 64 15:58:10.697087 IP 10.0.10.13 > 1.1.1.1: ICMP echo request, id 1620, seq 1, length 64 15:58:11.705736 IP 10.0.10.13 > 1.1.1.1: ICMP echo request, id 1620, seq 2, length 64 15:58:18.482031 IP 10.0.10.13 > 10.0.10.2: ICMP echo request, id 1622, seq 1, length 64 15:58:18.482061 IP 10.0.10.2 > 10.0.10.13: ICMP echo reply, id 1622, seq 1, length 64 15:58:19.481024 IP 10.0.10.13 > 10.0.10.2: ICMP echo request, id 1622, seq 2, length 64 15:58:19.481052 IP 10.0.10.2 > 10.0.10.13: ICMP echo reply, id 1622, seq 2, length 64 ^C 10 packets captured 10 packets received by filter 0 packets dropped by kernelHost config:
colin@host:~$ ifconfig br0 Link encap:Ethernet HWaddr 00:fd:45:fc:85:d8 inet addr:10.0.10.2 Bcast:10.0.255.255 Mask:255.255.0.0 inet6 addr: fe80::2fd:45ff:fefc:85d8/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:121153422 errors:0 dropped:715 overruns:0 frame:0 TX packets:65107786 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:172509978566 (172.5 GB) TX bytes:16134433818 (16.1 GB) br-df15cee8a6f6 Link encap:Ethernet HWaddr 02:42:74:28:3f:82 inet addr:172.20.0.1 Bcast:172.20.255.255 Mask:255.255.0.0 inet6 addr: fe80::42:74ff:fe28:3f82/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:158611 errors:0 dropped:0 overruns:0 frame:0 TX packets:402715 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:14673553 (14.6 MB) TX bytes:62211023 (62.2 MB) docker0 Link encap:Ethernet HWaddr 02:42:85:6b:5d:cd inet addr:172.17.0.1 Bcast:172.17.255.255 Mask:255.255.0.0 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:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) eno1 Link encap:Ethernet HWaddr 00:fd:45:fc:85:d8 inet6 addr: fe80::2fd:45ff:fefc:85d8/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:122992881 errors:0 dropped:14310 overruns:0 frame:0 TX packets:71313707 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:174820231625 (174.8 GB) TX bytes:16827079661 (16.8 GB) Interrupt:16 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:65536 Metric:1 RX packets:5163328 errors:0 dropped:0 overruns:0 frame:0 TX packets:5163328 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1 RX bytes:3075521109 (3.0 GB) TX bytes:3075521109 (3.0 GB) veth142ebf2 Link encap:Ethernet HWaddr 72:71:cc:8a:71:ff inet6 addr: fe80::7071:ccff:fe8a:71ff/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:111842 errors:0 dropped:0 overruns:0 frame:0 TX packets:278641 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:11860403 (11.8 MB) TX bytes:44222087 (44.2 MB) veth4bb7c84 Link encap:Ethernet HWaddr fe:17:53:a6:ea:ca inet6 addr: fe80::fc17:53ff:fea6:eaca/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:232661 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:18124977 (18.1 MB) veth7a2885b Link encap:Ethernet HWaddr d6:1c:ff:48:9d:e6 inet6 addr: fe80::d41c:ffff:fe48:9de6/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:232659 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:18124809 (18.1 MB) vnet0 Link encap:Ethernet HWaddr fe:54:00:7e:9d:e0 inet6 addr: fe80::fc54:ff:fe7e:9de0/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2800 errors:0 dropped:0 overruns:0 frame:0 TX packets:1339 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:267912 (267.9 KB) TX bytes:2975296 (2.9 MB)colin@host:~$ cat /etc/network/interfaces # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). source /etc/network/interfaces.d/* # The loopback network interface auto lo iface lo inet loopback # The primary network interface #auto eno1 #iface eno1 inet static #address 10.0.10.2 #netmask 255.255.0.0 #gateway 10.0.0.1 #dns-nameservers 10.0.0.1 # Bridge auto br0 iface br0 inet static address 10.0.10.2 netmask 255.255.0.0 gateway 10.0.0.1 dns-nameservers 1.1.1.1 bridge_ports eno1 bridge_stp off bridge_fd 0 bridge_maxwait 0colin@host:~$ sudo iptables -L -n -v [sudo] password for colin: Chain INPUT (policy ACCEPT 87M packets, 121G bytes) pkts bytes target prot opt in out source destination Chain FORWARD (policy DROP 2630 packets, 264K bytes) pkts bytes target prot opt in out source destination 5346 1299K DOCKER-USER all -- * * 0.0.0.0/0 0.0.0.0/0 5346 1299K DOCKER-ISOLATION-STAGE-1 all -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED 0 0 DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0 1278 872K ACCEPT all -- * br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED 0 0 DOCKER all -- * br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 1438 164K ACCEPT all -- br-df15cee8a6f6 !br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- br-df15cee8a6f6 br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT 49M packets, 16G bytes) pkts bytes target prot opt in out source destination Chain DOCKER (2 references) pkts bytes target prot opt in out source destination 0 0 ACCEPT tcp -- !br-df15cee8a6f6 br-df15cee8a6f6 0.0.0.0/0 172.20.0.3 tcp dpt:9000 0 0 ACCEPT tcp -- !br-df15cee8a6f6 br-df15cee8a6f6 0.0.0.0/0 172.20.0.4 tcp dpt:8181 Chain DOCKER-ISOLATION-STAGE-1 (1 references) pkts bytes target prot opt in out source destination 0 0 DOCKER-ISOLATION-STAGE-2 all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0 1438 164K DOCKER-ISOLATION-STAGE-2 all -- br-df15cee8a6f6 !br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 5346 1299K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 Chain DOCKER-ISOLATION-STAGE-2 (2 references) pkts bytes target prot opt in out source destination 0 0 DROP all -- * docker0 0.0.0.0/0 0.0.0.0/0 0 0 DROP all -- * br-df15cee8a6f6 0.0.0.0/0 0.0.0.0/0 1438 164K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 Chain DOCKER-USER (1 references) pkts bytes target prot opt in out source destination 5346 1299K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0Guest config:
colin@guest:~$ ifconfig eth0 Link encap:Ethernet HWaddr 52:54:00:7e:9d:e0 inet addr:10.0.10.13 Bcast:10.0.255.255 Mask:255.255.0.0 inet6 addr: fe80::5054:ff:fe7e:9de0/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1057 errors:0 dropped:256 overruns:0 frame:0 TX packets:2384 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2950816 (2.9 MB) TX bytes:228448 (228.4 KB) 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:65536 Metric:1 RX packets:141 errors:0 dropped:0 overruns:0 frame:0 TX packets:141 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1 RX bytes:22109 (22.1 KB) TX bytes:22109 (22.1 KB)colin@guest:~$ cat /etc/network/interfaces # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static address 10.0.10.13 netmask 255.255.0.0 network 10.0.0.0 broadcast 10.0.255.255 gateway 10.0.0.1 dns-nameservers 8.8.8.8 8.8.4.4I've been trying for weeks to solve this, but can't seem to make any headway.
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stratus about 4 yearsIn my case, I was using the default NAT interface and had the same problem. Same solution:
sudo iptables -I FORWARD -i virbr0 -o virbr0 -j ACCEPTThanks for sharing! -
coergo over 3 yearsMy exact issue on Ubuntu 20.04 after installing Docker then trying to get the bridged network working for KVM.
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erwin over 2 yearsTHANK YOU!!! THANK YOU!!! I've been fighting with this same issue in various permutations for weeks... Why in the world does every guide covering kvm setup leave out this step??? Anyway, if you've on Ubuntu 21.10 and later you need to use:sudo iptables-legacy -I FORWARD -i br0 -o br0 -j ACCEPT(same command, justiptables-legacyinstead of justiptables)
