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34 Cards in this Set
- Front
- Back
OSPF: Define LSU
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Link state update: packet that holds topology information, LSAs
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OSPF: Define LSA
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Link state advertisement. Information stored in the link-state database. |
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OSPF: Define Area
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A contiguous grouping of routers and routers interfaces. Routers in an area seek to learn all topology information about that area.
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OSPF: Define Area Border Router (ABR)
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A router that has interfaces in two distinct OSPF areas, one of which must be the backbone area. |
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OSPF: Define Backbone Router
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A router that has at least one interface connected to the backbone area, area 0. |
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OSPF: Define Internal Router
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A router that has interfaces connected to only one area. |
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OSPF: Define Designated Router
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On multiaccess interfaces (LAN), an OSPF router elected to play the key role in the database exchange process. |
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OSPF: Define Backup Designated Router
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On multiaccess interfaces (LAN) the BDR monitors the DR and is prepared to take over if the DR should fail.
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What are the basic IOS commands for configuring OSPF?
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#router ospf <process-id>
#network <net-addr> <wildcard> area <x> |
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What are the three major steps in the OSFP process?
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1. Neighbor discovery
2. Topology exchange (full network map) 3. Route computation - SPF algorithm |
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Do OSPF process-ids need to match in order to become neighbors?
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No.
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What is the OSPF procedure for choosing a router-id?
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1. Specified by #router-id <ip>
2. Highest IP address of up/up loopback interface 3. Highest IP address of up/up interface |
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What transport protocol is used by OSPF?
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IP, protocol type 89. Does not use TCP or UDP
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How is the OSPF router metric calculated?
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The cumulative cost of all outgoing interfaces in a route. Cost based on bandwidth by default.
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On which routers does OSPF support manual route summarization.
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Only on ABRs and ASBRs
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On which routers does OSPF support auto-summarization
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None. Never.
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What are the two OSPF timers used to determine convergence?
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1. Hello-timer (10 on LAN)
2. Dead timer (4 * Hello) |
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What are the three OSPF authentication types, and which is the default?
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Type 0 = No Authentication (default)
Type 1 = Clear Text Type 2 = Message Digest (MD5) |
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What is the maximum length of an OSPF authentication key?
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16 characters
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Does OSPF support authentication key-chains or time-based keys?
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No
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What are two ways to create a stable OSPF router id?
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1. set with #router-id
2. setup loopback interface |
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Describe the OSPF Type 1 LSA
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Router LSA.
LSID = Router-id Each router creates 1 for itself and floods through area. Lists RID and IP addresses on that router. ABRs create 1 for each area. |
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Describe the OSPF Type 2 LSA
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Network LSA
LSID = DRs IP addr in subnet Created by DR, for each multiaccess-network (LAN) LAN represented as a pseudonode, aka transit network Lists each router connected to pseudonode |
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What are the rules for electing an OSPF DR and BDR?
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1. Highest priority, based on interface mode command #ip ospf priority <n>
2. Highest RID 3. Follow same rules for BDR |
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When is an OSPF DR/BDR election held?
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If no DR/BDR exists, election held.
If DR fails, BDR becomes DR and new election is held for BDR. If BDR fails, same... No election when priorities change |
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Describe the OSPF Type-3 LSA
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Summary LSA.
LSID = Subnet number Created by ABR to summarize an area and advertise into other areas. |
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What are the three internal ospf LSA types?
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1. Router
2. Network 3. Summary |
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How does the OSPF routing algorithm differ for inter-area routes and intra-area routes?
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Inter-area routing uses distance-vector logic.
Intra-area routing uses SPF |
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What is the OSPF formula to calculate an interface cost?
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reference-bandwidth K / interface-bandwidth K
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What is the default OSPF reference bandwidth?
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100 Mbps
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What is the command and units to set the OSPF reference bandwidth?
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#auto-cost reference-bandwidth <x>
Units are M |
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What is the command to set the OSPF cost on an interface?
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#ip ospf cost <x>
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What is the default OSPF cost for a serial sub interface?
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Same as the serial interface.
1544 |
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What is the command to set the OSPF bandwidth on an interface?
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#bandwidth <x>
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