1. When EIGRP returns a stuck in active (SIA) message, it means that it has not received a reply to a query. An EIGRP neighbour (or neighbours) have not replied to the query for that route.
2. When the SIA occurs, the router clears the neighbour that did not reply to the query.

This is normal. On point-to-point and point-to-multipoint networks, there are no designated routers (DRs) or backup designated routers (BDRs).

1. EIGRP – 224.0.0.10
2. OSPF – for all the routers – 224.0.0.5
3. OSPF – initial multicast – only for DR and BDR – 224.0.0.6

1. Type-1 LSAs are router LSAs and are generated by each router for the area to which the router belongs.
2. Type-2 LSAs are network LSAs and are generated by the DR and BDR.

1. Broadcast, multi-access networks: Ehternet, token ring. Single mode operation.
2. Point-to-point : T1 CAS, ISDN BRI/PRI, single operation mode, no DR/BDR.
3. Non-broadcast multi-access(NBMA) networks: Frame realy, ATM, MPLS. Five modes of operation.