Double replies to ping

RouterOS General
1

Well this is a weird one…two replies to the same ping request sent.

Have an RB493, with ROS 5.7 and the firmware is upgraded to the latest version as well.

eth ports 3, 4, & 5 are set with eth2 as their ‘master’ port - in other words, 2, 3, 4, & 5 are set up as a switch.

Eth2 has two IP blocks. xxx.115.84.130/30 (so it’s gateway is xxx.115.84.129) and it has xxx.115.84.134/30 (it’s gateway is xxx.115.84.133)

In the routing table…0.0.0.0/0 gateway= xxx.115.84.129, xxx.115.84.133

In the local telco central office, we have a rather large cisco. That is the device the above RB493 is talking to. It has the corresponding gateway IP addresses on virtual interfaces.

On the cisco, I have set ARP to none, reply only, proxy-arp, and enabled.

I used the same settings (different combinations) on the MT RB493.

It does not matter what I ping, or what the above setting combinations are, I will get two replies for each ping sent.

Now I must also tell you here that I previously had a pc based 2.28 (yep - it was very OLD) with the exact (well exact as you can get in going from 2.28 to 5.7) configuration that only received 1 reply with each ping sent. The ONLY difference was that there was a switch (el’ cheapo dlink 5 port) in between the two DSL lines and the PC router.

I am in a quandry as to what this may be…I am leaning towards the RB as that is the only thing that has changed from the previous setup.

Any thoughts out there on this rather strange phenomena?

Thanks guys.

2

For all of you wanting to know why this is happening…read on.

I had originally removed the ‘el-cheapo’ switch I had had in place between the two DSL lines and my ‘main’ router Ethernet interface when I installed the new RB493 because I had set a number of Ethernet ports on the RB493 to emulate switch ports.

This appeared to work fine at first…but the the double ping replies showed up (showed up when I was testing ping to another device). Which I eventually tracked down to my Cisco at the central office replying to the ping request (remember now this is a layer 2 function, replying to the MAC address). Since my Cisco could ‘see’ both IP addresses and the RB could see both IP addresses of the Cisco, when I pinged something from the RB493, it ‘heard’ the answer from the Cisco twice…rather a sticky wicket in my opinion.

At any rate there seemed no way to stop this rather annoying behavior. Nothing I did on either the Cisco or the RB493 could stop the ping replies from being ‘heard’ twice.

I just installed another switch (Dell 16 port) and guess what…the unmanaged Dell switch keeps the reply from being heard twice…just like the ‘el-cheapo’ switch had done when I was using ROS 2.8 PC version…

There was one more thing that popped up during this whole evolution…there was a client that was playing second life…some type RPG…anyway, everytime this client chatted to another player his ‘chat’ showed up twice on his screen and the player to whom he was chatting to. Also, whenever he brought something, he would end up buying two of whatever it was. As you can imagine, this was rather annoying for the client!!

I just thought before all you inquiring minds starting pulling your hair out after having put some ports in to switch mode I’d let you know that switch mode isn’t exactly perfect under the current Mikrotik ROS version (5.7).