I have an Ubuntu 14 LTS server that has been in production for about 6 months.

Today I was making a routine tweak to the network configuration and everything went sideways. I have 4 vlan network interfaces that suddenly won't route traffic. I can't ping anything on any of those network interfaces.

I have rebooted the server several times and even restored to a backup from last night before I made any changes, but nothing will get these working.

At first I thought the problem may have been created by the datacenter network engineers, but I have added a couple Windows boxes to one of the vlans and they are communicating between each other fine, but can't ping the freeswitch on the vlan. UFW is disabled.

I have a eth0 which has two IP addresses and which continues to work fine:

auto eth0
iface eth0 inet static
hwaddress ether 00:50:56:b1:23:b0

auto eth0:0
iface eth0:0 inet static

I have 3 vlans which are point-to-point circuits coming in on dedicated interfaces ( I have obfuscated the public ip addresses ):

auto eth2
iface eth2 inet static
hwaddress ether 00:50:56:b1:71:7a
post-up route add -net netmask gw

auto eth3
iface eth3 inet static
hwaddress ether 00:50:56:b1:1c:cd
post-up route add -net netmask gw

auto eth4
iface eth4 inet static
address 144.?.?.206
hwaddress ether 00:50:56:b1:3d:10
post-up route add -net 199.?.?.67 netmask gw 144.?.?.205

There's a 4th vlan which is the one we tried to turn up today, I have removed the "post-up route add" because when I tried to add it, that's when things went sideways:

auto eth1
iface eth1 inet static
hwaddress ether 00:50:56:b1:82:59

Here is the routing table ( I obfuscated the public ip address ):

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface         UG    0      0        0 eth0   U     0      0        0 eth2   U     0      0        0 eth3
144.?.?.204 U     0      0        0 eth4   U     0      0        0 eth1   U     0      0        0 eth0 UG    0      0        0 eth2 UG    0      0        0 eth3
199.?.?.67      144.?.?.205 UGH   0      0        0 eth4

eth3 ( ) has been in production the longest. I have added two Windows computers to that vlan for troubleshooting purposes as and and they can ping each other but neither can ping, and the ubuntu server just gets this when trying to ping one of them:

itas@FreeSWITCH2:~$ ping
PING ( 56(84) bytes of data.
From icmp_seq=1 Destination Host Unreachable
From icmp_seq=2 Destination Host Unreachable
From icmp_seq=3 Destination Host Unreachable

Based on that ping output, it appears to be selecting the right interface, because is the ip on that interface, however "sudo tcpdump -i eth3" never shows a single packet in or out and "sudo tcpdump -i any icmp" shows this:

20:10:52.378575 IP > ICMP host unreachable, length 92

This looks like the icmp rejection never touches the "wire" ( this is a vmware environment ). Wireshark on the windows boxes never sees the icmp echo requests and I have configured VMware to allow promiscuous. One of the Windows boxes is on the same host and the other test one is on a different host.

From everything I've read, this looks like it should be a problem with the routing table, but I can't seem to find a problem with the routing table, and I can't seem to convince this box to send a packet out on eth3 or any of the vlan interfaces.

I'm at a complete loss as to what's wrong with all these network interfaces.

  • What does ifconfig -a eth3 show do you see any IPs on eth3 from arp -a? Can you ping Have you checked your VM settings? Are those interfaces in bridged mode? – meccooll Dec 2 '16 at 19:58
  • @meccooll I found the problem. Somehow my network adapters got shuffled and weren't in the same order any more. I thought the hwaddress field in /etc/network/interfaces allowed me to pin an interface to a nic but instead it allows me to overwrite the mac address. I have switched to a single nic using 8021q in ubuntu directly to avoid something like that from being able to happen again. – royce3 Dec 6 '16 at 12:18

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