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Webcast-Catalyst9k
New Member

MAC Address table --> "system" type entries

Hello,

Maybe someone could give me a definition or explanation of the mac-address table entries of "system" type ?

I find on many switches many entries with the broadcast address ffff.ffff.ffff defined by the system.

show mac address-table interface Gi1/16

Multicast Entries

vlan    mac address     type    ports

-------+---------------+-------+--------------------------------------------

  41    ffff.ffff.ffff   system Gi1/16,Gi1/23,Gi1/24,Gi3/7,Gi3/11,Gi3/16

                                Gi3/20,Gi3/23,Gi3/29,Gi3/47,Gi4/12,Gi4/13

                                Gi4/14,Gi4/22,Gi4/47,Gi7/23,Gi7/45,Gi7/47

                                Gi8/5,Gi8/6,Po6

Thanks !

4 REPLIES
Cisco Employee

MAC Address table --> "system" type entries

Hello Alex,

In my understanding, these entries are placed into the MAC address table to make sure that certain multicast and broadcast frames are (also) delivered to the CPU of the switch. Otherwise, broadcasts and specific multicasts (think CDP, VTP, STP and many more) would be simply switched through the switch without being processed by its CPU and in turn, the IOS. If you have a look at the show mac address-table without the interface specification, you will see that these specific multicast and broadcast MAC addresses have "CPU" as their outgoing interface.

Best regards,

Peter

New Member

MAC Address table --> "system" type entries

Ok, but the STP frames are sent to the MAC address of  01-80-C2-00-00-00, and CDP, VTP, DISL, PAgP, and DTP: 01-00-0C-CC-CC-CC, not to broadcast addresses.

And also, you are stating that all the broadcast frames are processed in software, and not in hardware ?

Thanks !

Cisco Employee

Re: MAC Address table --> "system" type entries

Hi Alex,

Ok, but the STP frames are sent to the MAC address of   01-80-C2-00-00-00, and CDP, VTP, DISL, PAgP, and DTP: 01-00-0C-CC-CC-CC,  not to broadcast addresses.

Correct. And they are also put into the MAC address table:

Switch# show mac address-table

          Mac Address Table

-------------------------------------------

Vlan    Mac Address       Type        Ports

----    -----------       --------    -----

All    0100.0ccc.cccc    STATIC      CPU

All    0100.0ccc.cccd    STATIC      CPU

All    0180.c200.0000    STATIC      CPU

All    0180.c200.0001    STATIC      CPU

All    0180.c200.0002    STATIC      CPU

All    0180.c200.0003    STATIC      CPU

All    0180.c200.0004    STATIC      CPU

All    0180.c200.0005    STATIC      CPU

All    0180.c200.0006    STATIC      CPU

All    0180.c200.0007    STATIC      CPU

All    0180.c200.0008    STATIC      CPU

All    0180.c200.0009    STATIC      CPU

All    0180.c200.000a    STATIC      CPU

All    0180.c200.000b    STATIC      CPU

All    0180.c200.000c    STATIC      CPU

All    0180.c200.000d    STATIC      CPU

All    0180.c200.000e    STATIC      CPU

All    0180.c200.000f    STATIC      CPU

All    0180.c200.0010    STATIC      CPU

All    ffff.ffff.ffff    STATIC      CPU

And also, you are stating that all the broadcast frames are processed in software, and not in hardware ?

Thanks !

Well, somebody from Cisco should give a definitive answer here but as far as my understanding goes, while the broadcasts/multicasts are not replicated by CPU, they are - at least for selected multicast/broadcast MAC addresses - delivered to the CPU together with being flooded through appropriate switchports. At least that is what the output of the show mac address-table tells me.

By the way, is what you originally posted really the output of the show mac address-table interface command? I've tried to replicate that on my 3560 but the format of the output was quite different.

Best regards,

Peter

New Member

Re: MAC Address table --> "system" type entries


I got the output from a WS-C4510R-E switch, and the nice part is that I don't see the CPU entries at all in the mac address table. Probably its something related to this model only.

Funny part is that I try to see on a 6500 switch and I do not see anything.

xxxxxx#  show mac address-table  | inc CPU

xxxxxx#  show mac address-table  | inc system

xxxxxxx#  show mac address-table  | inc fff

xxxxxx#

On WS-C3550-48-SMI I see only the CPU entries, without the ffff.

On WS-C3560-24TS the same...

2950 the same, only CPU.

Anyway I think it differs from model to model the way the mac address table is designed for 'view'. Until now I only saw 4500 that has both fff entries and CPU entries in the mac address table.

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