RIP route selection question

[dannan lin]

hi:

i am doing experiment with RIP.

the toppology is as follow

The RIP v2 set up was successful however when i try to  trace the packet , i realised the  the router on the right  always send packet via S3/0

why didn't it choose fa1/0 ? 

is it some kind of load balance? 

thanks in advance.

[Vaibhava Varma]

Hi Dannan

This does not seem to be any kind of load-balancing to me personally. Can you please share the output of below command

"sh ip route 1.1.1.1"  and "sh ip rip database "

Regards

Varma

[vipinrajrc]

Hi,

it is definetly not a load balace, since RIP is using hop count as metric.

Could you please provide output of "sh ip route"

Thanks

Vipin

[dannan lin]

thanks for your reply.

I think it could be load balance as well.  because i ran "trace 1.1.1.1 " command several times ,router choosed different port.

the output looks like below

  1   21.1.1.1        6 msec    3 msec    1 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   12.1.1.1        10 msec   5 msec    6 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   21.1.1.1        11 msec   4 msec    4 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   12.1.1.1        11 msec   6 msec    6 msec

below is the routing table:

     1.0.0.0/24 is subnetted, 1 subnets

R       1.1.1.0 [120/1] via 21.1.1.1, 00:00:28, FastEthernet1/0

                [120/1] via 12.1.1.1, 00:00:28, Serial3/0

     2.0.0.0/24 is subnetted, 1 subnets

C       2.2.2.0 is directly connected, Loopback0

     12.0.0.0/24 is subnetted, 1 subnets

C       12.1.1.0 is directly connected, Serial3/0

     21.0.0.0/24 is subnetted, 1 subnets

C       21.1.1.0 is directly connected, FastEthernet1/0     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 21.1.1.1, 00:00:28, FastEthernet1/0
                [120/1] via 12.1.1.1, 00:00:28, Serial3/0
     2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Loopback0
     12.0.0.0/24 is subnetted, 1 subnets
C       12.1.1.0 is directly connected, Serial3/0
     21.0.0.0/24 is subnetted, 1 subnets
C       21.1.1.0 is directly connected, FastEthernet1/0

if it is loadbalance ?  what kind of loadbalance is this ? (process based? )

is there any particular rule to choose which port to send packet first?

thanks for your help .

[Vaibhava Varma · Accepted solution]

Hi Dannan

RT has two equal cost paths for 1.1.1.1 and hence it has to load-balance but may be seems somewhere my understanding on interpreting the trace ouput is incoherent with the LB. This is a traffic which is originating from the router and not a transit traffic and hence should be process-switched on a round-robin basis.

Can you please try to traceroute multiple times with different source IPs ie once Source as 21.1.1.2 ( take 2 snapshots) and then source as 12.1.1.2 (take two snapshots)  and post the results.

Regards

Varma

[vipinrajrc · Accepted solution]

Hi,

R       1.1.1.0 [120/1] via 21.1.1.1, 00:00:28, FastEthernet1/0

                [120/1] via 12.1.1.1, 00:00:28, Serial3/0

From here it is clear that the remot n/w is learned by using two interface and it is of same cost. Since it is haveing same cost it will loadbalance with an algorithm called " round robin load balance".

Also RIP can support up to 6 equal path( 4 by default).

HTH

Please rate this post if you find this helpful

Thanks

Vipin

[dannan lin]

thanks guys,

\

it is a loadbalance , but i still want to know if there is any particular rule to use certain port to send packet first . in my case, why it aways choose 21.1.1.1 ????

below is my trace output :

Router#
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   21.1.1.1        30 msec   11 msec   1 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   12.1.1.1        33 msec   5 msec    6 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   21.1.1.1        25 msec   2 msec    5 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   12.1.1.1        21 msec   3 msec    3 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   21.1.1.1        25 msec   5 msec    3 msec   
Router#trace 1.1.1.1
Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1   12.1.1.1        24 msec   5 msec    4 msec   

thanks.

[Kishore Chennupati]

Hi Danna,

it is a loadbalance , but i still want to know if there is any particular rule to use certain port to send packet first . in my case, why it aways choose 21.1.1.1 ???? 

You can use something called PBR(policy based routing) where you can specify which interface the packet should exit from your device using "set-interface " command

please see the below link.

http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qcpolicy.html

HTH

Kishore