mjhjmtu

I'm running an Ubuntu server and I have plugged it into my local network. I've modified the /etc/network/interfaces file to look like this:

auto eth3
iface eth3 inet static
 address 192.168.1.15
 netmask 255.255.255.0
 gateway 192.168.1.1
 dns-nameservers 8.8.8.8

The interface comes up and shows the correct info. The network cards at hardware level are blinking and showing traffic. I can ping localhost.

I have run tcpdump on the interface and I'm seeing network traffic coming off card. By all accounts the network is up and running and I don't see any errors.

However, When I try to ping any computers on the network or try to ping back to this computer from other computers it is like it doesn't exist. I've been working with linux servers for 10+ years and never seen anything like this. Anyone have any ideas of what I might check?

ip a output:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
 valid_lft forever preferred_lft forever
 inet6 ::1/128 scope host 
 valid_lft forever preferred_lft forever
2: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
 link/ether 00:25:90:0a:eb:08 brd ff:ff:ff:ff:ff:ff
3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
 link/ether 00:25:90:0a:eb:09 brd ff:ff:ff:ff:ff:ff
 inet 192.168.1.10/24 brd 192.168.1.255 scope global eth3
 valid_lft forever preferred_lft forever
 inet6 fe80::225:90ff:fe0a:eb09/64 scope link 
 valid_lft forever preferred_lft forever
4: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100 
 link/none 
 inet 10.9.8.1 peer 10.9.8.2/32 scope global tun0
 valid_lft forever preferred_lft forever

ifconfig output:

eth3 Link encap:Ethernet HWaddr 00:25:90:0a:eb:09 
 inet addr:192.168.1.10 Bcast:192.168.1.255 Mask:255.255.255.0
 inet6 addr: fe80::225:90ff:fe0a:eb09/64 Scope:Link
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:1433 errors:0 dropped:0 overruns:0 frame:0
 TX packets:1115 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000 
 RX bytes:179713 (179.7 KB) TX bytes:128624 (128.6 KB) 
 Interrupt:17 Memory:feae0000-feb00000 

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:10 errors:0 dropped:0 overruns:0 frame:0
 TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:0 
 RX bytes:590 (590.0 B) TX bytes:590 (590.0 B)

tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 
 inet addr:10.9.8.1 P-t-P:10.9.8.2 Mask:255.255.255.255
 UP POINTOPOINT RUNNING NOARP 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:100 
 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

You have an active point-to-point VPN as can be seen by tun0; the VPN might be messing with local connectivity.

Many VPNs use what is know as full tunnel and mess with local connectivity for security reasons e.g. the "problems" you are describing are there by design, they are part of the intended security policy.

If you want to have local traffic, you have to turn off the VPN, but then you lose connectivity from whatever the other side that VPN is talking to.

Also the tun and dropped message packets on diagnostic data is a clue something fishy is going on. Seems that something/some software/a kernel module is dropped packets by design.