OSPF commands

Question 1

how to configure RID

Answer 1

en- conf t- router ospf 1- router-id 192.168.255.254(ip-addr)

Question 2

how to configure loop back address for routers

Answer 2

en-conf t- int loop 0- ip addr 192.196.255.254 (ipaddr)

Question 3

how to show all ospf info (what does it all show)

Answer 3

sh ip protocol
- show Royer ID
loopback adds
connected ip’s in which aread

Question 4

how to show neighbouring ospf

Answer 4

sh ip ospf neighbor

Question 5

How to configure routes to connected networks

Answer 5

en-conf t- router ospf 1 - network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.0 0.0.0.254 area 0
(network network-address wildcard-ask area area-id)
-ospf area is a group of routers that share link state info

Question 6

What is all part of the OSPF packet heacder

Answer 6

• Router ID
• Area id
• type of code for ospf packet type

Question 7

What is part of the IP packet header

Answer 7

-source ip addr, destination ip addr, protocol field set to 89

Question 8

OSPF packet types (5)

Answer 8

LAP

Question 9

OSPF interface priority command

what does that priority ave to be to ensure it is not a DR?

Answer 9

in config- if- ip ospf priority (0-255)
0- not able to be dr or bdr
1 deafult value
higher priority= DR

Question 10

what is OSPF costs

Answer 10

used to determine best route

cost based on bandwidth- 10*8/ bandwidth

Question 11

Router ID determined in the following order

Answer 11

• uses ip addr configured with the ospf router-id command
• if none configured- router chooses highest ip of any loopback interface
  -if none- router chooses highest ctive ip addr of physical interfaces
  (use sh ip protocol to see details)

Question 12

5 important ospf route sources and administractive distance

Answer 12

Connected - 0
Static - 1
ospf - 110
rip - 120

Question 13

Hello packets help to do what?
What is a DR
& BDR

Answer 13

Hello protocol packets contain info used to elect DR + BDR
DR- Designated router- responsable to update all other ospf routers
bdr- takes over is DR fails
** point to point links never have a DR****

Question 14

Hello packet does what?

Answer 14

• discovers neighbours and builds adjacencies between them
  b4- 2 routers can be adjacent they must have same values for :
• Hello interval, dead interval and Network type
  -HI_multicast=( 224.0.0.5) sent ever 30s
  DI- default is 4x hello time

Question 15

Database description (DBD) does?

Answer 15

checks database synchronization b/w routers

Question 16

Link-state request (LSR)

Answer 16

Requests specific link state records from router to router

Question 17

Link0state Update (LSU)

Answer 17

sends specifically requested link state records

Question 18

Link state acknowledgement (LSAck)

Answer 18

acknowledges other packet types

Question 19

The solution to LSA flooding is DR& DDR by?

Answer 19

routers are elected to send and receive LSA

• DRothers send LSA via multicast 244.0.0.6 to DR&BDR
• DR forwards LSA via multicast addr 244.0.0.5 to all other routers

Question 20

What is adjacency?

Answer 20

relationship b/w 2 routers that permit direct exchange of router updates
only shared routing info to adjacent neighbours

Question 21

Designated router

Answer 21

elected when OSPF routers are connected to the same broadcast network to minimize the number of adjacent networks & t publicize received routing info on a broadcast network or link

• elected the highest priority router
• all routers on the same network have synced routing tables

Question 22

Neighborship database

Answer 22

list of ospf routers where hello packets are sent

router id + state maintained on each router in db

Question 23

topological database

Answer 23

contains info from all the LSA Packets

computes the shortest path

Question 24

how is Router ID - RID configured

Answer 24

the ip addr used to identify the router
- cisco chooses RID by using highest ip add of loopback interfaces
if none then the highest ip of a physical interface

Question 25

neighbours

Answer 25

2 or more routers on a common network

must have same configurations: area id: stub area flag, hello and dead intervals

Question 26

what is a Link

Answer 26

Network or router interface assigned to any given network

will have up or down state and ip addr

Question 27

OSPF’s best features

Answer 27

• allows doe the creation of areas
• minimizes routing update traffic
• flexible, versatile, scalable
• supports vlsm/cidr
• offers an unlimited hopcount
• open + support multivendor deployment

Question 28

OSPF helps to

Answer 28

• confine network instability to single areas
• reduce overhead
• speeds up convergence

Question 29

OSPF must have?

Answer 29

• area 0 - the backbone
• Area border router (ABR)- router that connects other areas to the backbone
  Autonomous system boundary router- connecting multiple autonomous systems together

Question 30

Link State Advertisement LSA

Answer 30

OSPF data packet containing link state and routing info

ospf router exchanges LSA packets to adjacent routers

Question 31

OSPF area

Answer 31

• groups of networks and routers
• routers in same area share area id
• area id associated w/ specific interfaces on router
• area id can help scalability

Question 32

Broadcast/ multicast

Answer 32

allo multiple devices to connect or access same network

DR & BDR must be assigned

Question 33

Non Broadcast multi access (NBMA)

Answer 33

• this type of network allows multi-access without broadcast ability

Question 34

Point to mutipoint

Answer 34

network topology made up of a series of connection b/w single interface on one router and multiple destination router

Question 35

OSPF operations (3)

Answer 35

• neighbor + adjacent initialization
  _ LSA flooding
  _SPF tree calculations