OSPF Flashcards

1
Q

What are the 7 states OSPF neighbors go through?

A
  • Down
  • Attempt / Init
  • 2-way
  • EXSTART
  • Exchange
  • Loading
  • Full
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2
Q

In OSPF, what are the 5 types of LSAs?

A
  • Type 1 - Router LSA
  • Type 2 - Network LSA
  • Type 3 - Summary LSA
  • Type 4 - Summary ASBR LSA
  • Type 5 - External LSA
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3
Q

Which 5 items in the OSPF Hello protocol must match in order for an adjacency to form?

A
  • Hello and Dead Timers
  • Area ID
  • OSPF Area Type
  • Subnet
  • Authentication (if used)
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4
Q

What are the 4 Router Roles?

A
  • Backbone Routers
  • ASBR - Autonomous System Boundary Router
  • ABR - Area Border Router (also considered a Backbone Router)
  • Internal Router
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5
Q

What are the 3 Packet Types that are used during Database Synchronization?

A
  • DD - Database Description packets
  • LSR - Link-state Request packets
  • LSU - Link-state Update packets
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6
Q

What is a Type 1 LSA?

A
  • Name: Router LSA
  • Flooded to: Other routers in SAME AREA
  • Contains: Status of all the router’s Links in that area
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7
Q

What is a Type 2 LSA?

A
  • Name: Network LSA
  • Flooded by: DRs
  • Flooded to: SAME AREA
  • Contains: the state of other routers on the SAME NETWORK
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8
Q

What is a Type 3 LSA?

A
  • Name: Summary LSA
  • Flooded by: ABRs
  • Flooded to: an area that is EXTERNAL to the one where they were generated.
  • Contains: Networks and Inter-area Routes, IP address and RID of the sending ABR
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9
Q

What is a Type 4 LSA?

A
  • Name: Summary ASBR LSA
  • Flooded by: ABR
  • Flooded to: All areas EXTERNAL to where the LSA was generated.
  • Contains: Info letting all other OSPF Areas know how to get to the ASBR
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10
Q

What is a Type 5 LSA?

A
  • Name: External LSA
  • Flooded by: ASBR
  • Flooded to: everywhere
  • Contains: routes that are EXTERNAL to the OSPF Autonomous System
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11
Q

What are 3 features of an OSPF Hello packet itself?

A
  • follows IP packet header with protocol 89
  • sent via multicast 224.0.0.5 (all OSPF routers)
  • OSPF routers listen for them to find out about new neighbors
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12
Q

What 3 conditions have been met when a pair of neighbors reach 2-Way State?

A
  • They’ve exchanged Hellos
  • The parameters listed in the Hellos match.
  • They appear in each others neighbor table.
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13
Q

What is an LSA?

A
  • An LSA is a data structure, NOT a packet
  • Link State Advertisement
  • LSAs are sent to other routers in Link State Update packets (LSUs)
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14
Q

What is an Inter-area route?

A

A route to a subnet that is NOT in the local routers AREA.

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15
Q

What is an Intra-area route?

A

A route to a subnet that IS in the local routers AREA.

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16
Q

What is happening in the Down State?

A
  • Router initializing OSPF and chooses RID
  • Runs OSPF on interfaces configured for OSPF
  • Collects info to put in a Hello packet
17
Q

What is happening in the Attempt / Init state?

A
  • router has sent out Hello’s and is waiting for a response
  • if a neighbor goes down the router will try to re-establish neighborship by sending another Hello. This is Attempt.
18
Q

What is happening in the 2-Way State?

A
  • Both routers have exchanged HELLOs and matched config parameters
  • Both have exchanged Neighbor Tables and see each other
  • They’ve added each other to their Neighbor Tables
19
Q

What is happening in the EXStart State?

A
  • Master / Slave relationship created. Highest RID is Master. Master has to initiate exchange process.
  • Agree on initial sequence numbers
20
Q

What is happening in EXCHANGE State?

A
  • Routers send each other a list of LSAs in DD packets
  • The router checks the list of LSAs looking for LSAs that it doesn’t have.
  • LSRs are exchanged asking for networks they don’t already have
21
Q

What is happening during the Loading State?

A
  • Actual routing information is exchanged.
  • LSAs are exchanged in LSU packets
22
Q

What happens in the Full State?

A
  • Both routers are done exchanging LSAs
  • LSDBs on both routers are identical
23
Q

How is a Default Route configured in OSPF?

A
  • The route has to be in the routing table.
  • Configuration:
    • router ospf 10
      • default-information originate
24
Q

How can OSPF advertise a Default Route regardless of whether the route is in the routing table?

A
  • router ospf 10
    • default-information originate always
25
Q

What is the OSPF formula for calculate an interface cost?

A

100 MB / bandwidth

So, a serial interface running at 1MB would have an interface cost of 100. (100/1=100)