1. Ospf cannot use secondary ip to establish neighbor relationships
2. Only when the secondary ip and primary ip are in the same area can they be declared
3. There can be multiple DRs in an area, but there can only be one DR in a broadcast domain.
4. Ospf does not support unnumbered ip on the p2p link
5. Distribute-list can prevent routes from inserting into routing tables in the inbound direction, but cannot prevent lsa from entering lsdb. That is why outbound distributed-list does not work on the link state routing protocol, because it cannot prevent lsa from sending. But there are also special cases, when doing outbound distributed-list on Asbr, for example, ospf to eigrp, because outbound distributed-list can prevent routes from being sent.
6. You can use passive-interface to prevent the establishment of neighbor relationships
7. On the p2p link, even if the IP addresses of the two routers are not in the same network segment, they can establish neighbor relationships.
8. The routing order of ospf (from high to low): intra > inter > e1 > e2
9. How to set the router to DR without using the ip ospf priority command? router-id 223.255.255.255. Why not 255.255.255.255? Because bgp can only recognize 223.255.255.255.255. If you set a router-id greater than 223.255.255.255, there will be a problem with the redistribution between bgp and ospf (when doing redistribution between bgp and ospf, bgp and ospf must use the same router-id)
Some other redistribution notes:
1. Redistribution is only done once on the same router. If you redistribute the rip into ospf and then redistribute the ospf into isis, then the rip routes entering ospf will not automatically enter isis, so you need to redistribute the rip into isis.
2. When doing redistribution, you must add metric, because router does not know how to convert metrics of different protocols.
2. Only when the secondary ip and primary ip are in the same area can they be declared
3. There can be multiple DRs in an area, but there can only be one DR in a broadcast domain.
4. Ospf does not support unnumbered ip on the p2p link
5. Distribute-list can prevent routes from inserting into routing tables in the inbound direction, but cannot prevent lsa from entering lsdb. That is why outbound distributed-list does not work on the link state routing protocol, because it cannot prevent lsa from sending. But there are also special cases, when doing outbound distributed-list on Asbr, for example, ospf to eigrp, because outbound distributed-list can prevent routes from being sent.
6. You can use passive-interface to prevent the establishment of neighbor relationships
7. On the p2p link, even if the IP addresses of the two routers are not in the same network segment, they can establish neighbor relationships.
8. The routing order of ospf (from high to low): intra > inter > e1 > e2
9. How to set the router to DR without using the ip ospf priority command? router-id 223.255.255.255. Why not 255.255.255.255? Because bgp can only recognize 223.255.255.255.255. If you set a router-id greater than 223.255.255.255, there will be a problem with the redistribution between bgp and ospf (when doing redistribution between bgp and ospf, bgp and ospf must use the same router-id)
Some other redistribution notes:
1. Redistribution is only done once on the same router. If you redistribute the rip into ospf and then redistribute the ospf into isis, then the rip routes entering ospf will not automatically enter isis, so you need to redistribute the rip into isis.
2. When doing redistribution, you must add metric, because router does not know how to convert metrics of different protocols.