Can the nat on an interface cause a gre problem with Cisco router? Eee

RouterOS General
1

Hello,

I want to ask u have a cisco router and Mikrotik router
Both have public IPS BUT the protocol is down on cisco router when I tried to configure GRE tunnel between both of them

I want ask can the Nat on the Mikrotik router is the reason for this problem?

I can ping between the two PUBLIC IPS but the protocol of the GREon cisco is down

Best regards

2

NAT may be the root cause of the problem if the gre tunnel configuration at the Mikrotik side uses a different local address for the GRE packets than the public one.
Another cause of the problem may be a tight firewall at Mikrotik side and keepalive activated at Cisco side.
Yet another problem may be the security update at 6.45.something, after which the Mikrotik firewall started labeling GRE packets with connection-state=invalid.

Show your complete configuration export from the Mikrotik side, the output of /ip firewall connection print detail where protocol~“gre”, and the GRE configuration on Cisco. Before posting, see my automatic signature below on how to properly anonymize the information without breaking its consistency.