Hello Damien
Thanks for sharing your solution with us… Just a comment on the particular error message you’re getting. This is a somewhat common issue that is encountered when using CEF. The “adjacency fixup” message typically indicates that CEF couldn’t properly find an entry for the next-hop address in its adjacency table, leading to packet drops.
Removing ip cef resolved the issue because it forces the router to revert to process switching, which may handle the packets differently, particularly in simulation environments like EVE-NG with specific IOS versions. But I’m still not quite sure of the reason for your original CEF malfunction. It could be due to incompatibility of the IOS, or maybe some CEF parameter that was configured? If you’re interested, consider doing some troubleshooting with CEF activated, we’d be interested in hearing your results…
I hope this has been helpful!
Laz