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CCNA Volume 1 > Vol 1 Part 6: OSPF > Flashcards

Vol 1 Part 6: OSPF Flashcards

1
Q

What are the 4 routing protocols used for learning routes?

A
  1. RIP
  2. EIGRP
  3. OSPF
  4. BGP
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2
Q

If more than one possible route exists to reach one subnet, what does a router do to pick the appropriate route?

A

It picks the best route based on a metric.

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3
Q

What are the two major IP routing protocols?

A

Interior gateway protocol (IGP) and exterior gateway protocol (EGP)

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4
Q

What is IGP designed to be used with?

A

Inside a single autonomous system, (AS) ie a company, a website, etc.

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5
Q

What is EGP designed to be used with?

A

Between different autonomous systems ie. apple and microsoft, spectrum and comcast etc.

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6
Q

What are the three main branches of IGPs?

A
  1. Distance Vector (AKA Bellman-Ford)
  2. Advanced Distance Vector (AKA Balanced Hybrid)
  3. Link-state
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7
Q

What are the 3 categories of the distance vector IGP?

A
  1. RIPv1
  2. RIPv2
  3. IGRP (Cisco proprietary)
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8
Q

What kind of IGP is OSPF?

A

Link-state

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9
Q

What Cisco proprietary IGP (no longer cisco proprietary) is faster than OSPF, and what kind of IGP is it considered?

A

EIGRP. It is a Hybrid/Advanced Distance Vector

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10
Q

What metric does RIPv2 use when picking the best route?

A

Hop count (number of routers/hops between a router and the destination subnet)

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11
Q

What metric does OSPF use when picking the best route?

A

Cost (sum of all the interface cost settings for all links in a route, with the cost defaulting based on interface bandwidth)

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12
Q

What metric does EIGRP use when picking the best route?

A

Composite of bandwidth and delay (calculated based on the route’s slowest link and the cumulative delay associated with each interface in the route)

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13
Q

Which IGPs are classless (sends mask in updates/supports VLSM)?

A

RIPv2, EIGRP, and OSPF. RIPv1 is NOT classless.

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14
Q

Which IGPs support manual summarization and which ones do not?

A

RIPv2, EIGRP, and OSPF support manual summarization. RIPv1 does not.

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15
Q

When two companies use different routing protocols such as OSPF and EIGRP and they MUST communicate, what must happen so that each router has the appropriate routes?

A

route redistribution

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16
Q

What does OSPF use to exchange data about networks between routers?

A

Link State Advertisements (LSAs)

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17
Q

What command is used to show the LSA database?

A

Show ip ospf database

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18
Q

How often do routers re-flood each LSA?

A

Every 30 minutes

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19
Q

What are the three phases that OSPC uses to accomplish LSA exchange and calculate routes?

A
  1. Become neighbors
  2. Exchange LSA databases
  3. Adding the best routes by running the SPF algorithm, based on the local copy of the LSA Database (LSDB)

Remember! A router can calculate the best routes from that routers perspective and add it to its own IPv4 routing table!

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20
Q

What must be in place in order to become neighbors with another router?

A
  1. Same data link and use OSPF
  2. Same VLAN, serial link, or ethernet WAN link
  3. Use OSPF hello messages between routers
  4. OSPF parameter compatibility
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21
Q

What command is used to see a router’s neighbord?

A

show ip ospf neighbor

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22
Q

What does a router have that is unique to in and identifies it on the network?

A

A router ID (RID). It is simply the router’s IPv4 address.

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23
Q

How does a router obtain a neighbor’s RID?

A

With a Hello message

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24
Q

The Hello message follows an IP packet header with IP protocol BLANK?

A

type 89

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25
Q

Hello packets are sent to a multicast IP of BLANK for all OSPF speaking routers

A

244.0.0.5

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26
Q

What two timers MUST be the SAME for all routers on a link in order to establish a neighbor relationship?

A

The Hello and Dead timers

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27
Q

When establishing neighbors, both routers start down and then enter what state? And what happens after each router is in this state?

A
  1. INIT

2. The routers send RIDs between each other

28
Q

Once both RIDs are seen, the routers enter what state (hint: its the state after INIT)?

A

2-WAY

29
Q

If a router does not have an LSA, it will ask for it specifically to get the details of the network information it contains. The message that sends the LSAs is called what?

A

Link Status Updates (LSUs)

30
Q

What is happening on a router if it is in the loading state?

A

It is loading the LSAs it needs

31
Q

What is meant when two routers are in the full state?

A

They are fully adjacent and have identical LSDBs

32
Q

How often is the hello timer?

A

Every 10 seconds (by default)

33
Q

How often is the dead timer?

A

4 times the hello (default of 4*10=40 seconds)

34
Q

On ethernet links, the OSPF protocol elects two types of routers. What are these two routers called, and what do they do?

A

The Designated Router (DR)- Responsible to ensure that all routers get a copy of each LSA
The Backup Designated Router (BDR)- takes over for the DR in the event that it fails

35
Q

What is the multi cast address for all SPF DRs?

A

226.0.0.6

36
Q

What term is used to refer to a non-DR?

A

DROTHER

37
Q

What is true about DROTHER routers with respect to their relationship between each other?

A

All DROTHERs will be 2-WAY with each other. This means they do not update or exchange LSDBs with each other.

38
Q

What area is the typical default area for OSPF?

A

Area 0 (the backbone area). REMEMBER! All other areas must connect to area 0!

39
Q

What command is used to see a router’s LSBD?

A

show ip ospf database

40
Q

What are the three types of LSAs and what do they do?

A

Type 1. router LSA- used for each router in the area
Type 2. network LSA- used for each network that has a DR plus on neighbor of the DR. This is the LSA that is flooded by the DR.
Type 3. summary LSA- used to summarize the areas for other routers. It is sent out by the Area Border Router (ABR)

41
Q

What is an area border router?

A

An OSPF router with interfaces connected to the backbone area and to at least one other area

42
Q

What are the contents of a router LSA?

A

RID, interfaces, IP address/mask, current interface status

43
Q

What are the contents of a network LSA?

A

DR and BDR ip addresses, subnet ID, mask

44
Q

What are the contents of a summary LSA?

A

Subnet ID, mask, RID of ABR that advertises the LSA

45
Q

What command is used to enter the OSPF configuration mode?

A

router ospf #

46
Q

When configuring the OSPF router-ID, what two commands can you use?

A
  1. router-id x.x.x.x

2. interface loopback 0 (with an IP/mask)

47
Q

What must you do to enable OSPF v2 on an interface?

A

Use one or more “network x.x.x.x x.x.x.x area x” commands matched by the configured address and mask

48
Q

What do wildcard masks do?

A

Give the local router its rules for matching its own interfaces

49
Q

What are the types of Wildcards?

A
  1. 0.0.0- matches only one IP exactly
  2. 0.0.255- matches the first three octets
  3. 0.255.255- matches the first two octets
  4. 222.222.222- matches the first octet
  5. 255.255.255- ignores everything. NOT recommended.
50
Q

What does the “FULL/ - “ neighbor state mean?

A

The neighbor state is full, but the - means that the link does NOT use a DR/BDR. This is most likely used in a point to point configuration.

51
Q

What does the “FULL/DROTHER” neighbor state mean?

A

The router is a full neighbor with a router that is neither a DR or BDR. This implies that the local router is a DR or BDR.

52
Q

What does the “show ip protocols” command do?

A

Provides a brief and very useful summary of any routing protocol running

53
Q

What does the “show ip ospf interface” command do?

A

Verifies if the router enabled OSPF on the interface with details

54
Q

What does the “show ip ospf interface brief” command do?

A

Verifies if the router enabled OSPF on the interface with a summary

55
Q

What does the passive-interface command do when enabled, and why do we do it?

A

It configures the router to not send or respond to hello packets, but it will still advertise the network on the interface defined. We may do this on a layer 2 switch or for a router on a link with no other router. This allows us to advertise the network, but not spend time with hello packets that simply aren’t necessary.

56
Q

What is a default route with respect to OSPF and why do we use it?

A

A route used for all traffic going to the internet. We want all of our routers to have a default route so that all packets destined to locations in the internet go to the one router that is connected to the internet.

57
Q

How do we create and flood a default route?

A

default-information originate

REMEMBER! This is only configured on your edge/internet router

58
Q

What are the 3 ways we can change the OSPF interface cost?

A
  1. ip ospf cost x
  2. changing the interface bandwidth with the “interface bandwidth x” command. Should be avoided if possible.
  3. changing the OSPF reference bandwidth with the auto-cost reference-bandwidth ref-bw with a unit in Mbps. Ideally you’d set the bandwidth tot he highest supported bandwidth interface speed.
59
Q

How do we load balance on OSPF?

A

Using the maximum-paths x command where the x value sets the number of permitted routes in the routing table. Our x value is defaulted to 1, and can be no higher than 4.

60
Q

What are the to different network types based on interface in OSPF?

A

Broadcast and point-to-point

61
Q

Which type of network uses a DR/BDR and which type does no?

A

A broadcast network will use a DR/BDR, but a point-to-point network will not

62
Q

What command is used to change the network type?

A

ip ospf network

63
Q

What command is used to wipe a router’s OSPF database?

A

clear ip ospf process

64
Q

What command is used to change the router’s OSPF priority?

A

ip ospf priority x where x is a value between 0 and 255. The default priority is 1, and the higher priority means that the router is more likely to become the DR. A priority value of 0 means that the router will NEVER participate in DR/BDR elections.

65
Q

If two routers have mismatching network types, they can still become neighbors. They will also exchange LSDBs. What, however, will not happen?

A

The routers will not add IP routes to the IP routing table, meaning the neighbor relationship is unusable as the routers are never added.

CCNA Volume 1 (8 decks)

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