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
Use the configuration from the lab 34 (four loopbacks created).
- Loopback 1: 10.0.0.1/24
- Loopback 2: 10.0.1.1/24
- Loopback 3: 10.0.2.1/24
- Loopback 4: 10.0.1.1/24
Task 2
On R3 advertise the four loopbacks (1-4) as LSA5.
Task 3
Configure R3 so that it sends warning when the number of prefixes reaches 3 redistributed LSAs. But first warning should be sent when 60 percent of the threshold is reached. Check the results.
Task 4
Change the redistributed limit to 3 prefixes. If the number of prefixes redistributed into OSPF exceeds this number the excess should be rejected. Check the results.
Task 5
OSPF process on R1 should not exceed 15% to allow other process to operate. The maximum LSAs R1 can accept is 1500.
Lab Solution
Task 1
R3 Configuration:
R3 Configuration:
Verification:
All four subnets are showing in LDSB on R3 (show ip ospf database external).
Task 3
R3 Configuration:
Note!
Entered a config and after a few seconds the following system messages were sent to console 0.
Verification:
Note!
The 'warning-only' keyword still allows more LSAs than the maximum threshold (here 3 LSA5).
Task 4
R3 Configuration:
Verification:
Note!
Only 3 LSAs Type5 are accepted by OSPF.
Task 5
Use the configuration from the lab 34 (four loopbacks created).
- Loopback 1: 10.0.0.1/24
- Loopback 2: 10.0.1.1/24
- Loopback 3: 10.0.2.1/24
- Loopback 4: 10.0.1.1/24
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
!
interface Loopback2
ip address 10.0.1.1 255.255.255.0
!
interface Loopback3
ip address 10.0.2.1 255.255.255.0
!
interface Loopback4
ip address 10.0.3.1 255.255.255.0
ip address 10.0.0.1 255.255.255.0
!
interface Loopback2
ip address 10.0.1.1 255.255.255.0
!
interface Loopback3
ip address 10.0.2.1 255.255.255.0
!
interface Loopback4
ip address 10.0.3.1 255.255.255.0
!
Task 2
On R3 advertise the four loopbacks (1-4) as LSA5.
R3 Configuration:
!
ip prefix-list LOOPBACKS seq 5 permit 10.0.0.0/22 le 24
!
route-map CONNECTED_TO_OSPF permit 10
match ip address prefix-list LOOPBACKS
!
match ip address prefix-list LOOPBACKS
!
!
Verification:
All four subnets are showing in LDSB on R3 (show ip ospf database external).
Pic. 2 - R3's LSDB Content.
Configure R3 so that it sends warning when the number of prefixes reaches 3 redistributed LSAs. But first warning should be sent when 60% of the threshold is reached. Check the results.
R3 Configuration:
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
redistribute maximum-prefix 3 60 warning-only
redistribute connected subnets route-map CONNECTED_TO_OSPF
network 10.1.13.3 0.0.0.0 area 13
network 172.16.103.3 0.0.0.0 area 13
router-id 3.3.3.3
log-adjacency-changes
redistribute maximum-prefix 3 60 warning-only
redistribute connected subnets route-map CONNECTED_TO_OSPF
network 10.1.13.3 0.0.0.0 area 13
network 172.16.103.3 0.0.0.0 area 13
!
Note!
Entered a config and after a few seconds the following system messages were sent to console 0.
Verification:
Pic. 3 - System Logs.
Note!
The 'warning-only' keyword still allows more LSAs than the maximum threshold (here 3 LSA5).
Pic. 4 - R3's LSDB Has 4 LSA5.
Pic. 5 - R1's routing table.
Change the redistributed limit to 3 prefixes. If the number of prefixes redistributed into OSPF exceeds this number the excess should be rejected. First warning should be sent when the maximum threshold of 3 reaches 60%. Check the results.
R3 Configuration:
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
redistribute maximum-prefix 3 60
redistribute connected subnets route-map CONNECTED_TO_OSPF
network 10.1.13.3 0.0.0.0 area 13
network 172.16.103.3 0.0.0.0 area 13
router-id 3.3.3.3
log-adjacency-changes
redistribute maximum-prefix 3 60
redistribute connected subnets route-map CONNECTED_TO_OSPF
network 10.1.13.3 0.0.0.0 area 13
network 172.16.103.3 0.0.0.0 area 13
!
Verification:
Pic. 6 - LSA Threshold Messages.
Only 3 LSAs Type5 are accepted by OSPF.
Pic. 7 - R3's LSDB Type-5.
Pic. 8 - R3 OSPF Output.
OSPF process on R1 should not exceed 15% to allow other process to operate. The maximum LSAs R1 can accept is 1500.
R1 Configuration:
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
max-lsa 1500
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
max-lsa 1500
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. 9 - Max LSA
