Another good read on the same topic.https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13684-12.html

Hi @mfatty  The simple solution to this problem is to use same MTU on both end routers running OSPF in the case of Cisco Routers. Although this becomes a bit complex when different vendor equipment is being used as each vendor may implement implement...