Lab 1 - OSPF Point-to-Point Mode - Solution

Lab 1 - OSPF Point-to-Point Mode - Solution
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) 
Q5:
Are hello packets sent using unicast or multicast?
Answer:
    Since point-to-point connections support multicast (like broadcast networks), multicast 224.0.0.5 is going to be used when sending hello packets. 

    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. 
    Q8:
    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
    Q9:
    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
    Also, their hello and dead interval timers must be tweaked. They use 30/120 whereas point-to-point use 10/40.

    Q10:
    Without using the 'network' statement, how can you advertise the subnet 10.1.1.0/24?
    Answers:
    Quick solutions could be:
    1. The interface command: 'ip ospf 1 area 0' (here 1 is the process ID).
    2. Redistribution of connected networks into OSPF.
    As for the solution to the tasks, here goes...

    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
    !

    R3 Configuration:
    !
    interface Loopback0
     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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