| Description |
This article shows how to fix the OSPF adjacency issue with the error 'packet duplicated (slave)' on one side and 'Neighbor state is less than Exchange' on the other side. |
| Scope |
FortiGate. |
| Solution |
The error will look like the below screenshot under Log & Report -> Router Events and the OSPF adjacency state from 'get router info ospf neighbor' will be in exstart.
The error will be visible as well from the output of 'OSPF debug logs'. with below commands:
diagnose ip router ospf all enable diagnose ip router ospf level info diagnose debug enable To disable the debug:
diagnose debug disable
The cause of this issue is MTU.
config router ospf config ospf-interface set mtu-ignore enable <----- end
If this did not fix the issue, then go for option 2:
execute ping-options source x.x.x.x <----- IP address assigned to this side of the link execute ping-options data-size xxxx <----- data size [0,65507]. execute ping-options df-bit yes <----- set DF bit to 1. execute ping y.y.y.y <----- IP address assigned to the other side.
Note the max data size on which the ping was successful with 'df-bit yes' and configure the link MTU to that value:
config system interface edit <name> <----- OSPF interface. set mtu-override enable set mtu xxx <-- the max data size obtain from ping test. end
Change the MTU on both sides. If the link is a VPN tunnel, configure the MTU override under the IPSec interface and not on the physical interface, so other traffic is not impacted by this change.
Restart the OSPF process after the interface MTU has been adjusted, and the neighbors should come up and show FULL. |
