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17 Cards in this Set
- Front
- Back
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What algorithm does OSPF use to calculate metric?
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Dijkstra SPF algorithm
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What information is sent in LSU packets?
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Link state updates contain a subnet number, mask, metric, and other information about the subnet.
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What is the multicast destination address used for OSPF Hello packets?
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224.0.0.5
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What is a Hello packet and what does it contain?
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It allows OSPF neighbors to meet each other. It contains the sending router's RID, Area ID, Hello interval, dead interval, router priority, designated router, backup designated router, and a list of neighbors that the sending router already knows about on the subnet.
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What information MUST two OSPF routers agree on in order to become neighbors?
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Subnet mask. Subnet number. Hello interval. Dead interval. OSPF Area ID.
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What is a DR, and what is its purpose?
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Designated Router. Required for OSPF on LANs, and sometimes Frame Relay and ATM. Essentially, other OSPF routers send their updates to the DR and it distributes them to the other routers on the subnet. The idea is to cut down on redundant OSPF traffic.
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How does OSPF decide whether it needs a DR or not, and how can you control that behavior?
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It depends on the OSPF network type. You can change it with "ip ospf network [type]".
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What is a BDR?
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Backup Designated Router.
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How is a DR elected?
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The router sending the Hello with the highest OSPF Priority setting becomes the DR. If a new router comes on and advertises a higher priority it does not immediately become the DR - it has to wait for the current DR and BDR to fail.
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How can you tell when a router has exchanged its entire link-state database with a neighbor?
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It enters the "Full" state. "show ip ospf neighbor'.
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What is the dead interval?
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If a router doesn't hear a Hello from a neighbor within the dead interval, it assumes the link is down, removes information about that router from its database, and runs the Dijkstra algorithm again.
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What are the issues OSPF faces as it scales to larger networks?
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A larger topology database requires more memory on each router. Processing the larger topology database with the SPF algorithm requires processing power that grows exponentially with the size of the database. A single interface change forces every router to run SPF again.
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How can you mitigate the scaling problems faced by managing OSPF in larger networks?
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Use OSPF areas to limit the amount of information each router needs to know about all the other routers on the network.
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What category routing protocol is EIGRP?
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Balanced Hybrid.
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What is the basic process used by EIGRP to communicate with other routers?
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Neighbor discovery. Full routing update. Continuous Hellos (5 seconds by default on LANs and PPP links). Partial updates when there are changes.
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How does EIRGP avoid loops?
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When it builds the topology table it includes other routes that could be used if the best route fails. The second best is called the successor, and the rest are called feasible successors. If there are no successors in the topology table, the router uses the Diffusing Update Algorithm (DUAL) to send queries to its neighbors to locate another route.
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What tables does EIRGP keep?
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Neighbors table, topology table, and routing table.
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