Question on limit to dynamically learned MAC addresses per vlan

I'm trying to troubleshoot connectivity problems between a virtual server at a central site and PCs in the same vlan at a remote site. At the central site is several VMWare servers connected to a 3560 switch. The PCs at the remote site need to reach this virtual server, and while most do, some have trouble seeing it.

A common thread seems to be whether the 3560 has been able to learn the MAC address of the PC. If it hasn't, we can put in a static address and everything is OK.

I'm wondering... is there a limit to the number of dynamic MAC addresses that a switch like the 3560 can learn? If so, can that limit be changed, and is the situation the same for static addresses?

Also, is the limit of total MAC addresses for the switch fixed, or can that be changed?


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Just wanted to follow up with some more details on this network set up...

[remote side 4500] ----> (CSME) ----> [central side 4500] ----> (ATM)

----> [central side 8540] ----> [vmware 3560] ----> [vmware server]

the remote side has a vlan, let's call it 321, and the vmware server has a virtual machine set up for vlan 321. Most remote machines find the vmware server, and some find it one minute and not the next.

The remote side has about 330 MAC addresses in the vlan in question. The central side 4500 never seems to learn more than about 200 or so. I'm assuming that the central side 4500 learns mac addresses from the remote side, and passes it through the 8540 (configured for IRB) to the 3560. None of the central side devices seem to learn much more than 200 of the MAC addresses and I'm not sure where that limitation would be. Does anyone have any idea what's going on here?

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I don't recall a per VLAN limit but the MAC adddress table in switches is implemented in hardware and there is a total limit. It is certain to be way more than 330 though thousands and thousands.

Ah! 8540!

Maybe I should have mentioned when I indicated the IRB config earlier that the 8540 etc. was a somewhat problematical device. Wouldn't touch one with a barge pole.

Remember that "missing" MAC addresses do not normally cause a lack of communications since frames to Unknown addresses are flooded out of all ports in the VLAN and so do reach the destination.

I will have a closer look later and see of I can think how to investigate.

Is this the Network with Unicast Flooding Prevention turned on? That simply limits all normal traffic to some level. Maybe that was another thread. Sorry, bit busy right now and cant check. If it is turn it off.

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This issue turned out to be a limit to learned MAC addresses on the CSME (AT&T) side. Increasing the limit made all problems go away... Thanks for your help!

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