Lab 34 - OSPF Discard Route

Lab 34 - OSPF Discard Route
Di Posting Oleh : Simple Learning
Kategori : Core Technologies OSPF Routing

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:

• 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

Advertise these subnets in area 13 with their configured network mask.

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.

Lab Solution

Task 1

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

Advertise these subnets in area 13 with their configured network mask.

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

!

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

!

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

!

Verification:

Pic. 3 - R1's Routing Table: Discard Route Created.

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.

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

!

Pic. 4 - R1's Routing Table: Discard Route Removed.

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