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mac-address-table synchronize

Dears

Would like your assistance please regarding command "mac-address-table synchronize"

My understanding is that it syncs CAM table between different DFCs & RSP PFC

 

So If we are having only one DFC there would be no need for this command. It will only be useful in case we are having several DFCs or there is a communication between DFC and ports connected in RSP.

1- Correct ?

 

2- Is SVI interface considered to be part of DFC or PFC ?

I am asking this cause if part of PFC then this command would be needed

 

Many Thanks

Regards

Sherif Ismail

7 REPLIES

DearsAny idea ? Thanks

Dears

Any idea ?

 

Thanks

Cisco Employee

Sherifismail,I see that its

Sherifismail,

I see that its already been answered anyway again:

My understanding is that it syncs CAM table between different DFCs & RSP PFC

==Answer is yes.

 

So If we are having only one DFC there would be no need for this command. It will only be useful in case we are having several DFCs or there is a communication between DFC and ports connected in RSP.

1- Correct ? 

Answer: No you still required. else sometime you might see the mac address present in the software and not on the module.

 

2- Is SVI interface considered to be part of DFC or PFC ?

I am asking this cause if part of PFC then this command would be needed

Answer: I would believe it would be part of PFC.

 

HTH

 

Hi EdMany thanks for your

Dears

Many thanks for your replies

Sorry i didnt see first reply probably a problem in mobile update.

 

1- One last thing please would there be any router memory worries if i configured this command as now CAM table for whole modules will be synced.

 

2- As I understand if this command is not configured unicast flooding will occur thus links with low bandwidth may be affected, right ?

 

Many thanks for your assistance

 

Regards

Sherif Ismsil

 

Cisco Employee

Hi,1- One last thing please

Hi,

1- One last thing please would there be any router memory worries if i configured this command as now CAM table for whole modules will be synced.

Answer: no router memory worries. 

2- As I understand if this command is not configured unicast flooding will occur thus links with low bandwidth may be affected, right ?

Answer:Yes you are right. I had seen this very badly.

 

HTH

Regards

Inayath

Hi InayathMany thanks .. You

Hi Inayath

Many thanks .. You are a network saver :)

This may explains the myth of unicast flooding we had in our network. According to documentation this behavior should only occur If we are having asymmetric routing or HSRP with load-balancing. In our case we had HSRP routers where all active groups were in one router so theoretically we  should not have unicast flooding especially that we are having one DFC ES+ card and no ports connected to RSP ports.

But now my guess (thanks to your replies) this happened cause SVI interfaces are part of PFC so flooding will occur between DFC & L3 SVIs @ PFC. So in our case either "mac-address-table synchronize" or adjusting CAM to be equal that of ARP would have solved the issue. I have applied the 2nd one cause was still studying the effect of "mac-address-table synchronize"

Hope my analysis is correct :)

Once again many thanks

One thing that is still a

One thing that is still a myth for me why we didn't encounter any unicast flooding on standby HSRP router.

My understanding is that when flooded traffic reaches R2 (standby router) it should also be flooded , right ?

 

Many thanks in advance

Regards

Sherif Ismail

Cisco Employee

Sherifismail,For both

Sherifismail,

For both questions: The command is useful to sync the MAC address tables between the RSP and DFC or DFCs, even if there is only one as they have their own.

Kind regards,

- Ed

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