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AUsquirrel
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Joined: Fri Feb 21, 2014 10:28 pm

Strange Ping problem

Sun May 22, 2022 12:32 pm

Hi Everyone,
I have a really strange network problem that I have run out of ideas to fault find so am asking for suggestions. I have a dude server and it can't communicate with one of my other routers. I have been investigating it and found some interesting results when using ping and traceroute to locate the problem

The Setup:

All routers are running RouterOS 7.2.3

I have three routers A, B and C. Router A has the Dude server.
A and B are connected by a /30 subnet. This is a normal router to router link with two VLANS, a management and a traffic VLAN.
B and C are connected by a wireguard link also with a /30 subnet and no VLANs.
All three routers have one or more /24 subnets connected to them and you can ping to any subnet from any other subnet except when blocked by a firewall rule. I can ping from A to B and B to A to both IPs in router link and to the connected subnets were permitted. I can ping from the subnet connected to A to both ends of the B-C wireguard link and the gateway IP for the router C /24 subnet as well as to devices on that subnet. So from what I can tell all the routes are correct.

The two things that aren't happening are that I can't ping from router A to either interface on router C, wireguard and gateway nor to the subnet connected to it. I also can't ping from Router C to the link IP addresses for the traffic link on the router A to router B link. I can ping from router C to two of the subnet interface IPs on router A which includes management VLAN IP.

When I use torch I can see the ICMP packets returning from router C to router A from a ping from A to C on the traffic link between A and B. I just get a time out as if the packets are being dropped at the link interface. As all the other pings to the router interface are working, that tend to suggest that the firewalls aren't the issue.
The logs show no indication of any issues and checking the firewall counters show no correlating count to packets dropped or received.

Any pointers on where to look next are greatly appreciated.

Thanks

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