Which two of the following are contained in an OSPF hello packet? (Choose two.)
A.
hello interval
B.
dead interval
C.
ex-start
D.
link-state update
Explanation:
Hello Packet:Hello packets are OSPF packet Type 1. These packets are multicast periodically to 224.0.0.5 multicast address on all interfaces (unicast on virtual-links) enabling dynamic discovery of neighbors and maintain neighbor relationships. On broadcast and NBMA networks, Hello packets are used to elect DR and BDR.
Network Mask – Subnet mask of the advertising OSPF interface. For unnumbered point-to-point interfaces and virtual-links, it is set to 0.0.0.0 (4-bytes)
HelloInterval – Interval at which Hello packets are advertised. By default, 10 seconds for point-to-point link and 30 seconds for NBMA/Broadcast links (2-bytes)
Options – The local router advertises its capabilities in this field. (1-byte)
Rtr Pri – The Priority of the local router. It is used for DR/BDR election. If set to 0, the router is ineligible for the election. (1-byte)
RouterDeadInterval – The Dead Interval as requested by the advertising router. By default, 40 seconds for point-to-point link and 120 seconds for NBMA/Broadcast links (4-bytes)
Designated Router – The IP address of the current DR. Set to 0.0.0.0 if no DR is elected yet. (4-bytes)
Backup Designated Router – The IP address of the current BDR. Set to 0.0.0.0 if no BDR is elected yet. (4-bytes)
Neighbor – The Router IDs of all OSPF routers from whom a valid Hello packet have been seen on the network.The following is a sample packet capture of an OSPF Hello packet.
The fields Area ID, HelloInterval, RouterDeadInterval and Authentication information (AuType & Authentication) should match on neighbors to form adjacency. For example, when the Hello interval is changed on a router, the receiving router does not accept the Hello packet due to mismatch of Hello timer. The following message is displayed.
