Di Posting Oleh : Simple Learning
Kategori : Core Technologies Fundamentals OSPF Routing Video
Prerequisites: CCNP level skills.
This post contains the answers and configuration for the LAB 1.
Answers
Q1:
What is the default OSPF mode of operation on F1/0 interface?
Answer:The default OSPF mode of operation is 'broadcast'.
Q2:
Are hello packets sent using unicast or multicast?
Answer:
Hello packets will use multicast 224.0.0.5.
Q3:
Does F1/0 interface participate in DR/BDR election? Why?
Answer:Yes, since broadcast and NBMA interfaces do participate in DR/BDR election unless have been configured with the priority=0.
The reason for electing DR/BDR on broadcast and NBMA networks is to limit the propagation of LSAs. DRother routers establish full adjacency with DR and BDR only. DRothers establish 2-way adjacency with other routers in DRother role.
Q4:
What is the default OSPF mode of operation on S0/1 interface?
Answer:The default encapsulation on S0/1 is HDLC which is point-to-point protocol.
The default OSPF mode is point-to-point. This is the default OSPF mode on the following:
- Interfaces running point-to-point protocols (HDLC, PPP)
- Subinterfaces configured as point-to-point (int s0/1.point-to-point)
Are hello packets sent using unicast or multicast?
Answer:
Q6:
Does it participate in DR/BDR election? Why?
Answer:
OSPF point-to-point mode does not participate in the election of DR/BDR since there are only two routers echanging LSAs. There is no excess of LSA exchanges typical for multi-access networks.
Q7:
What are the default hello and dead interval timers used on F1/0 and S0/1?
Answer:
On both interfaces the timers are:
- hello=10 seconds
- dead=40 seconds.
Is there any other OSPF mode of operation that could work with the default OSPF mode on F1/0? What would you have to do to make it work?
Answer:
The default OSPF mode on broadcast networks is broadcast.
You can configure OSPF-enabled interface with NBMA mode which also elect DR/BDR. In order to make them work together you have to adjust the timers as they are not same between these two modes. NBMA mode uses:
- hello=30 seconds
- dead=120 seconds
Is there any other OSPF mode of operation that could work with the default OSPF mode on S1/0? What would you have to do to make it work?
Answer:The default OSPF mode on S0/1 (HDLC encapsulation) is point-to-point.
The "somewhat" compatible modes of operation with the 'point-to-point' are:
- point-to-multipoint
- point-to-multipoint nonbrodcast
Q10:
Without using the 'network' statement, how can you advertise the subnet 10.1.1.0/24?
Answers:Quick solutions could be:
- The interface command: 'ip ospf 1 area 0' (here 1 is the process ID).
- Redistribution of connected networks into OSPF.
Pic. 1 - OSPF Point-to-Point Topology.
Icons designed by: Andrzej Szoblik - http://www.newo.pl
R1 Configuration:
!
interface Loopback0
ip address 172.16.101.1 255.255.255.0
!
interface Serial0/1
ip address 10.1.13.1 255.255.255.0
!
router ospf 1
log-adjacency-changes
network 10.1.1.1 0.0.0.0 area 0
network 10.1.13.0 0.0.0.255 area 0
!
ip address 172.16.101.1 255.255.255.0
!
interface Serial0/1
ip address 10.1.13.1 255.255.255.0
!
router ospf 1
log-adjacency-changes
network 10.1.1.1 0.0.0.0 area 0
network 10.1.13.0 0.0.0.255 area 0
!
R3 Configuration:
!
interface Loopback0
ip address 172.16.103.3 255.255.255.0
!
ip address 172.16.103.3 255.255.255.0
!
interface Serial0/1
ip address 10.1.13.3 255.255.255.0
!
router ospf 1
log-adjacency-changes
network 10.1.3.3 0.0.0.0 area 0
network 10.1.13.0 0.0.0.255 area 0
!
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