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Accepted
Johannes Ernst
Asked: 2013-07-29 20:16:37 +0800 CST

libvirt guest cannot reach outside world

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My server connects to the public internet via eth0 (50.131.xxx.xxx). The same server connects to the LAN via eth1 (192.168.138.1 on 192.168.138.0/24) On the same server, I run libvirt, which created another subnet at 192.168.122.0/24. The currently only guest is at 192.168.122.10.

I'm trying to get routing on the server set up, and I'm stuck.

From my laptop on the LAN (192.168.138.18), I can ssh into the guest, the server, and the public internet. However, I can only partially do the reverse: From my guest, I can ssh into the server but I cannot ssh into the laptop, or reach the public internet.

This is Ubuntu 12.04 LTS on the server, and 13.04 on the guest.

On the guest:

guest> traceroute serverfault.com
 1  192.168.122.1 (192.168.122.1)  0.644 ms  0.577 ms  0.564 ms
 2  * * *

(and so forth)

Here's some data that hopefully helps somebody more knowledgeable than me.

guest> ip r
default via 192.168.122.1 dev eth0 
192.168.122.0/24 dev eth0  proto kernel  scope link  src 192.168.122.10 

server> cat /proc/sys/net/ipv4/ip_forward 
1

server> ifconfig
eth0      Link encap:Ethernet  HWaddr 6c:f0:49:0e:09:b2  
      inet addr:50.131.xxx.xxx  Bcast:255.255.255.255  Mask:255.255.252.0
      UP BROADCAST RUNNING MULTICAST  MTU:576  Metric:1
      RX packets:670219 errors:0 dropped:0 overruns:0 frame:0
      TX packets:532895 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:271653035 (271.6 MB)  TX bytes:70403086 (70.4 MB)
      Interrupt:41 

eth1      Link encap:Ethernet  HWaddr 00:c0:49:fa:1f:da  
      inet addr:192.168.138.1  Bcast:192.168.138.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:539044 errors:0 dropped:0 overruns:0 frame:0
      TX packets:563204 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:72237497 (72.2 MB)  TX bytes:272391132 (272.3 MB)
      Interrupt:19 Base address:0x2000 

lo        Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      UP LOOPBACK RUNNING  MTU:16436  Metric:1
      RX packets:14143 errors:0 dropped:0 overruns:0 frame:0
      TX packets:14143 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:8000728 (8.0 MB)  TX bytes:8000728 (8.0 MB)

virbr0    Link encap:Ethernet  HWaddr 52:54:00:9e:51:10  
      inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:1655 errors:0 dropped:0 overruns:0 frame:0
      TX packets:2067 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:188811 (188.8 KB)  TX bytes:242584 (242.5 KB)

vnet0     Link encap:Ethernet  HWaddr fe:54:00:cf:1f:41  
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:1655 errors:0 dropped:0 overruns:0 frame:0
      TX packets:4105 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:500 
      RX bytes:211981 (211.9 KB)  TX bytes:348362 (348.3 KB)

server> brctl show
bridge name bridge id          STP enabled  interfaces
virbr0      8000.5254009e5110  yes          virbr0-nic
                                            vnet0

server> ip route
default via 50.131.xxx.1 dev eth0  metric 100 
50.131.xxx.0/22 dev eth0  proto kernel  scope link  src 50.131.xxx.xxx 
192.168.122.0/24 dev virbr0  proto kernel  scope link  src 192.168.122.1 
192.168.138.0/24 dev eth1  proto kernel  scope link  src 192.168.138.1 

server> virsh net-list
Name                 State      Autostart
-----------------------------------------
default              active     yes       

server> virsh net-edit default
<network>
 <name>default</name>
 <uuid>ddc855bf-8794-f4de-f1f9-7480edf9f419</uuid>
 <forward mode='route'/>
 <bridge name='virbr0' stp='on' delay='20' />
 <mac address='52:54:00:9E:51:10'/>
 <ip address='192.168.122.1' netmask='255.255.255.0'>
  <dhcp>
   <range start='192.168.122.100' end='192.168.122.254' />
   <host mac='52:54:00:cf:1f:41' name='guest.example.com' ip='192.168.122.10' />
  </dhcp>
 </ip>
</network>

server> tail /etc/sysctl.conf
...
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

I also run ufw. It says:

server> ufw status verbose
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing)
New profiles: skip


To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere
53/tcp                     ALLOW       192.168.138.0/24
53/udp                     ALLOW       192.168.138.0/24
21                         ALLOW       192.168.138.0/24
192.168.138.0/24           ALLOW       192.168.138.0/24
192.168.122.0/24           ALLOW       192.168.138.0/24
192.168.138.0/24           ALLOW       192.168.122.0/24
192.168.122.0/24           ALLOW       192.168.122.0/24

To me, it sounds like something really obvious, but then, not to me it seems ...

-- Added: The behavior is the same even if I disable ufw. But here is the output of iptables-save:

# Generated by iptables-save v1.4.12 on Mon Jul 29 08:57:10 2013
*mangle
:PREROUTING ACCEPT [4511095:1341076448]
:INPUT ACCEPT [79374:20510726]
:FORWARD ACCEPT [4428917:1318506209]
:OUTPUT ACCEPT [72504:23698077]
:POSTROUTING ACCEPT [4501421:1342204286]
-A POSTROUTING -o virbr0 -p udp -m udp --dport 68 -j CHECKSUM --checksum-fill
COMMIT
# Completed on Mon Jul 29 08:57:10 2013
# Generated by iptables-save v1.4.12 on Mon Jul 29 08:57:10 2013
*nat
:PREROUTING ACCEPT [33012:2764507]
:INPUT ACCEPT [16436:1476129]
:OUTPUT ACCEPT [10423:864202]
:POSTROUTING ACCEPT [10487:868042]
-A POSTROUTING -s 192.168.138.0/24 -o eth0 -j MASQUERADE
-A POSTROUTING -s 192.168.138.0/24 -o eth0 -j MASQUERADE
COMMIT
# Completed on Mon Jul 29 08:57:10 2013
# Generated by iptables-save v1.4.12 on Mon Jul 29 08:57:10 2013
*filter
:INPUT DROP [1335:71456]
:FORWARD ACCEPT [3360867:988924571]
:OUTPUT ACCEPT [18:936]
:ufw-after-forward - [0:0]
:ufw-after-input - [0:0]
:ufw-after-logging-forward - [0:0]
:ufw-after-logging-input - [0:0]
:ufw-after-logging-output - [0:0]
:ufw-after-output - [0:0]
:ufw-before-forward - [0:0]
:ufw-before-input - [0:0]
:ufw-before-logging-forward - [0:0]
:ufw-before-logging-input - [0:0]
:ufw-before-logging-output - [0:0]
:ufw-before-output - [0:0]
:ufw-logging-allow - [0:0]
:ufw-logging-deny - [0:0]
:ufw-not-local - [0:0]
:ufw-reject-forward - [0:0]
:ufw-reject-input - [0:0]
:ufw-reject-output - [0:0]
:ufw-skip-to-policy-forward - [0:0]
:ufw-skip-to-policy-input - [0:0]
:ufw-skip-to-policy-output - [0:0]
:ufw-track-input - [0:0]
:ufw-track-output - [0:0]
:ufw-user-forward - [0:0]
:ufw-user-input - [0:0]
:ufw-user-limit - [0:0]
:ufw-user-limit-accept - [0:0]
:ufw-user-logging-forward - [0:0]
:ufw-user-logging-input - [0:0]
:ufw-user-logging-output - [0:0]
:ufw-user-output - [0:0]
-A INPUT -i virbr0 -p udp -m udp --dport 53 -j ACCEPT
-A INPUT -i virbr0 -p tcp -m tcp --dport 53 -j ACCEPT
-A INPUT -i virbr0 -p udp -m udp --dport 67 -j ACCEPT
-A INPUT -i virbr0 -p tcp -m tcp --dport 67 -j ACCEPT
-A INPUT -j ufw-before-logging-input
-A INPUT -j ufw-before-input
-A INPUT -j ufw-after-input
-A INPUT -j ufw-after-logging-input
-A INPUT -j ufw-reject-input
-A INPUT -j ufw-track-input
-A FORWARD -d 192.168.122.0/24 -o virbr0 -j ACCEPT
-A FORWARD -s 192.168.122.0/24 -i virbr0 -j ACCEPT
-A FORWARD -i virbr0 -o virbr0 -j ACCEPT
-A FORWARD -o virbr0 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -i virbr0 -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -j ufw-before-logging-forward
-A FORWARD -j ufw-before-forward
-A FORWARD -j ufw-after-forward
-A FORWARD -j ufw-after-logging-forward
-A FORWARD -j ufw-reject-forward
-A OUTPUT -j ufw-before-logging-output
-A OUTPUT -j ufw-before-output
-A OUTPUT -j ufw-after-output
-A OUTPUT -j ufw-after-logging-output
-A OUTPUT -j ufw-reject-output
-A OUTPUT -j ufw-track-output
-A ufw-after-input -p udp -m udp --dport 137 -j ufw-skip-to-policy-input
-A ufw-after-input -p udp -m udp --dport 138 -j ufw-skip-to-policy-input
-A ufw-after-input -p tcp -m tcp --dport 139 -j ufw-skip-to-policy-input
-A ufw-after-input -p tcp -m tcp --dport 445 -j ufw-skip-to-policy-input
-A ufw-after-input -p udp -m udp --dport 67 -j ufw-skip-to-policy-input
-A ufw-after-input -p udp -m udp --dport 68 -j ufw-skip-to-policy-input
-A ufw-after-input -m addrtype --dst-type BROADCAST -j ufw-skip-to-policy-input
-A ufw-after-logging-input -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] "
-A ufw-before-forward -j ufw-user-forward
-A ufw-before-input -i lo -j ACCEPT
-A ufw-before-input -m state --state RELATED,ESTABLISHED -j ACCEPT
-A ufw-before-input -m state --state INVALID -j ufw-logging-deny
-A ufw-before-input -m state --state INVALID -j DROP
-A ufw-before-input -p icmp -m icmp --icmp-type 3 -j ACCEPT
-A ufw-before-input -p icmp -m icmp --icmp-type 4 -j ACCEPT
-A ufw-before-input -p icmp -m icmp --icmp-type 11 -j ACCEPT
-A ufw-before-input -p icmp -m icmp --icmp-type 12 -j ACCEPT
-A ufw-before-input -p icmp -m icmp --icmp-type 8 -j ACCEPT
-A ufw-before-input -p udp -m udp --sport 67 --dport 68 -j ACCEPT
-A ufw-before-input -j ufw-not-local
-A ufw-before-input -d 224.0.0.251/32 -p udp -m udp --dport 5353 -j ACCEPT
-A ufw-before-input -d 239.255.255.250/32 -p udp -m udp --dport 1900 -j ACCEPT
-A ufw-before-input -j ufw-user-input
-A ufw-before-output -o lo -j ACCEPT
-A ufw-before-output -m state --state RELATED,ESTABLISHED -j ACCEPT
-A ufw-before-output -j ufw-user-output
-A ufw-logging-allow -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW ALLOW] "
-A ufw-logging-deny -m state --state INVALID -m limit --limit 3/min --limit-burst 10 -j RETURN
-A ufw-logging-deny -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] "
-A ufw-not-local -m addrtype --dst-type LOCAL -j RETURN
-A ufw-not-local -m addrtype --dst-type MULTICAST -j RETURN
-A ufw-not-local -m addrtype --dst-type BROADCAST -j RETURN
-A ufw-not-local -m limit --limit 3/min --limit-burst 10 -j ufw-logging-deny
-A ufw-not-local -j DROP
-A ufw-skip-to-policy-forward -j ACCEPT
-A ufw-skip-to-policy-input -j DROP
-A ufw-skip-to-policy-output -j ACCEPT
-A ufw-track-output -p tcp -m state --state NEW -j ACCEPT
-A ufw-track-output -p udp -m state --state NEW -j ACCEPT
-A ufw-user-input -p tcp -m tcp --dport 22 -m comment --comment "\'dapp_OpenSSH\'" -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -p tcp -m tcp --dport 53 -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -p udp -m udp --dport 53 -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -p tcp -m tcp --dport 21 -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -p udp -m udp --dport 21 -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -d 192.168.138.0/24 -j ACCEPT
-A ufw-user-input -s 192.168.138.0/24 -d 192.168.122.0/24 -j ACCEPT
-A ufw-user-input -s 192.168.122.0/24 -d 192.168.138.0/24 -j ACCEPT
-A ufw-user-input -s 192.168.122.0/24 -d 192.168.122.0/24 -j ACCEPT
-A ufw-user-limit -m limit --limit 3/min -j LOG --log-prefix "[UFW LIMIT BLOCK] "
-A ufw-user-limit -j REJECT --reject-with icmp-port-unreachable
-A ufw-user-limit-accept -j ACCEPT
COMMIT
# Completed on Mon Jul 29 08:57:10 2013
linux

1 Answers

  1. Best Answer

    Have you set the ip address of the guest machine statically?

    Make sure it has a correct default route aswell.

    Please provide the output from ip r or netstat -ra on the guest.

    Can you ping hosts on your local network (the 192.168.138.1) from the guest? Then try to ping one step further away from the guest. An easy host to remember is 8.8.8.8 at google.

    Since there may be a NAT issue, where you only NAT the 192.168.138.0 network.

    See theese two lines in UFW.

    -A POSTROUTING -s 192.168.138.0/24 -o eth0 -j MASQUERADE
-A POSTROUTING -s 192.168.138.0/24 -o eth0 -j MASQUERADE
    • 2