OSPF Path Selection explained

Lessons Discussion
58

Hi ,

I want load balance my icmp traffic over ospf on attached topology , so that number of icmp req/res should be shared equaly on GigabitEthernet1/0 and GigabitEthernet2/0 . i understand currently all icmp traffic(50 req and 50 res packets) getting forwarded/received through the link R1-R2 as ospf taking lowest router id of 10.1.1.2(R2) compared 10.1.1.3(R3) . How to achieve loadbalace the traffic so that i can get 50 Req + Res on the link R1-R2 and similarly 50 Req + Res on R1-R3 ?

Sending traffic

R1#ping  200.200.200.200 source loopback 0 repeat 50

Type escape sequence to abort.
Sending 50, 100-byte ICMP Echos to 200.200.200.200, timeout is 2 seconds:
Packet sent with a source address of 100.100.100.100
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 100 percent (50/50), round-trip min/avg/max = 48/63/80 ms

  1. i have tried with maximum-paths 2 on R1 , below is my observations :
    50 icmp reply packets on the link from R1-R2 . And 50 ICMP Request on the link R1-R3 (shown as no response found on wireshark capture)

  2. i have deleted maximum-paths 2 config and tried with command traffic-share min across-interfaces command → 50 icmp Req and 50 responses through the link R1-R2 . (Same beha)

  3. I configured R1 and R6 maximum-paths 2, behaviour is the same as case 1 as above.

Below is the common config for R2,R3,R4 and R5 :

router ospf 100
 router-id 10.1.1.2
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area 0
!

On R1 : Extra interface is interface loopback 0 --100.100.100.100

R1#sho ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
10.1.1.3          1   FULL/DR         00:00:33    192.168.13.3    GigabitEthernet2/0
10.1.1.2          1   FULL/DR         00:00:33    192.168.12.2    GigabitEthernet1/0

R1#sho ip route 200.200.200.200
Routing entry for 200.200.200.200/32
  Known via "ospf 100", distance 110, metric 4, type intra area
  Last update from 192.168.13.3 on GigabitEthernet2/0, 00:13:23 ago
  Routing Descriptor Blocks:
    192.168.13.3, from 10.1.1.6, 00:13:23 ago, via GigabitEthernet2/0
      Route metric is 4, traffic share count is 1
  * 192.168.12.2, from 10.1.1.6, 00:13:23 ago, via GigabitEthernet1/0
      Route metric is 4, traffic share count is 1

On R6 : Extra interface is interface loopback 0 --200.200.200.200

R6#sho ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
10.1.1.5          1   FULL/DR         00:00:36    192.168.56.5    GigabitEthernet2/0
10.1.1.4          1   FULL/DR         00:00:31    192.168.46.4    GigabitEthernet1/0

R6#sho ip route 100.100.100.100
Routing entry for 100.100.100.100/32
  Known via "ospf 100", distance 110, metric 4, type intra area
  Last update from 192.168.56.5 on GigabitEthernet2/0, 00:19:52 ago
  Routing Descriptor Blocks:
    192.168.56.5, from 10.1.1.1, 00:19:52 ago, via GigabitEthernet2/0
      Route metric is 4, traffic share count is 1
  * 192.168.46.4, from 10.1.1.1, 00:19:52 ago, via GigabitEthernet1/0
      Route metric is 4, traffic share count is 1

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