Prerequisites: CCNP level skills.
Personal Note!
A horrible tragedy happened in Japan today. Earthquake (8.8 on Richter scale) hit this country and sparked tsunami. It is a terrible event of cataclysmic proportions.
My great sympathy to all who have suffered due to this unexpected calamity.
Note!
When OSPF summarizes prefixes (area range or summary-address) it installs a discard route in the routing table (pointing to NULL0). This is a loop prevention mechanism that prevents a router from sending the traffic to a network/subnet with a shorter match if no more specific route exists in the routing table.
Topology
Pic. 1 - OSPF Topology.
Icons designed by: Andrzej Szoblik - http://www.newo.pl
Task 1
Configure the following loopback interfaces on R3:
Task 2
Configure the following loopback interfaces on R3:
- Loopback 1: 10.0.0.1/24
- Loopback 2: 10.0.1.1/24
- Loopback 3: 10.0.2.1/24
- Loopback 4: 10.0.3.1/24
Task 2
On R1 summarize Loopbacks 1-4. Make sure the summary route does not overlap with other addresses. Check R1's routing table to find out what was installed after configuring this summarization.
Task 3
Make sure R1 does not have a summary address pointing to NULL0 interface (discard route) in its routing table. The reachability should be maintained.
Task 3
Make sure R1 does not have a summary address pointing to NULL0 interface (discard route) in its routing table. The reachability should be maintained.
Lab Solution
Task 1
R3 Configuration:
Verfication:
Task 2
Configure the following loopback interfaces on R3:
- Loopback 1: 10.0.0.1/24
- Loopback 2: 10.0.1.1/24
- Loopback 3: 10.0.2.1/24
- Loopback 4: 10.0.3.1/24
R3 Configuration:
!
interface Loopback1
ip address 10.0.0.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback2
ip address 10.0.1.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback3
ip address 10.0.2.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback4
ip address 10.0.3.1 255.255.255.0
ip ospf network point-to-point
ip address 10.0.0.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback2
ip address 10.0.1.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback3
ip address 10.0.2.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback4
ip address 10.0.3.1 255.255.255.0
ip ospf network point-to-point
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
network 10.1.13.3 0.0.0.0 area 13
network 10.0.0.0 0.255.255.255 area 13
network 172.16.103.3 0.0.0.0 area 13
router-id 3.3.3.3
log-adjacency-changes
network 10.1.13.3 0.0.0.0 area 13
network 10.0.0.0 0.255.255.255 area 13
network 172.16.103.3 0.0.0.0 area 13
!
Verfication:
Pic. 2 - R1's Routing Table.
Task 2
On R1 summarize Loopbacks 1-4. Make sure the summary route does not overlap with other addresses. Check R1's routing table to find out what was installed after configuring this summarization.
R1 Configuration:
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
area 13 range 10.0.0.0 255.255.252.0
network 10.1.12.1 0.0.0.0 area 0
network 10.1.13.1 0.0.0.0 area 13
network 172.16.101.1 0.0.0.0 area 0
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
area 13 range 10.0.0.0 255.255.252.0
network 10.1.12.1 0.0.0.0 area 0
network 10.1.13.1 0.0.0.0 area 13
network 172.16.101.1 0.0.0.0 area 0
!
Verification:
Pic. 3 - R1's Routing Table: Discard Route Created.
Make sure R1 does not have a summary address pointing to NULL0 interface (discard route) in its routing table. The reachability should be maintained.
R1 Configuration:
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
no discard-route internal
area 13 range 10.0.0.0 255.255.252.0
network 10.1.12.1 0.0.0.0 area 0
network 10.1.13.1 0.0.0.0 area 13
network 172.16.101.1 0.0.0.0 area 0
router-id 1.1.1.1
log-adjacency-changes
no discard-route internal
area 13 range 10.0.0.0 255.255.252.0
network 10.1.12.1 0.0.0.0 area 0
network 10.1.13.1 0.0.0.0 area 13
network 172.16.101.1 0.0.0.0 area 0
!
Pic. 4 - R1's Routing Table: Discard Route Removed.
