I have an odd problem with two of my MikroTik routers. They are running as x86 VMs under Ubuntu KVM.

Setup:
- Ubuntu 12.04 LTS running KVM. Each firewall is on a separate Ubuntu machine.
- Two MikroTik routers running 5.24
- Ether1: Public interface with public IP (dedicated and VRRP). All inbound traffic uses the VRRP public IP, no issues.
- Ether2: Internal interface with internal IP (dedicated and VRRP). There are mapped to a physical interface on the Ubuntu machine that has various VLAN's configured. The VLAN interface is set up on Ubuntu and the VLAN interface is used in the KVM configuration so the MikroTik is not "aware" of the VLAN.
- Running NAT on the public VRRP interface, no problems there
- Publishing (dst-nat) rule for inbound SMTP to a Microsoft NLB address.

Everything works great except for an internal Microsoft NLB address. Here is the problem that occurs:

- Router 1: Can ping internal MS NLB (192.168.0.5) without issue. Manual telnet to a port on that IP works. Never has an issue communicating with the internal MS NLB address.
- Router 2: Cannot ping internal MS NLB (192.168.0.5). ARP entry exists in the ARP table but the ping fails. Forcing ping to come from the dedicated IP also times out.

It doesn't appear to be any issue with the NLB since all of the other machines on the VLAN can ping and access 192.168.0.5 which would also seem to eliminate the switch as a problem.

The packet sniffer shows traffic going out ether2 when traffic is initiated from router2. But no ping replies.

I was wondering if anyone had any ideas on why this would happen or ideas of what to look at more closely?

This only happens with the Microsoft NLB address.

I created a new MikroTik VM on the same Ubuntu machine with the problem VM (unable to ping NLB address). This MikroTik x86 didn't have VRRP and had the same interfaces set up. This VM also was unable to ping the NLB (192.168.0.5).

I set up another MikroTik VM on the Ubuntu machine that didn't have any issues and it was able to ping the NLB without issues.

The problem appears to be with my KVM configuration on Ubuntu so I'll dig through that issue. No issues with MikroTik.

If anyone has suggestions, feel free to post them but clearly this is an issue with the KVM configuration.