How is the mac for the rootbridge chosen on a Cat5000?

[snitram]

Hello,

as generally known in a switched lan the rootbridge is elected concerning priority and in case of a tie concerning the lowest mac.

Regarding the output of "sh spant <vlan>" on a Cat5000 I can get the see the mac of the rootbridge.

Switch (enable) sh spant 300

VLAN 300

Spanning tree enabled

Spanning tree type ieee

Designated Root 00-50-d1-33-c5-2b

Designated Root Priority 8192

Designated Root Cost 3

This leads me to my question. Where is this mac coming from at a Cat5000? What rules does apply concerning the election of the mac. Any ideas welcome.

Best regards, Snitram

[mtorelli · Accepted solution]

Snitram,

The Cat5000 chooses the spanning-tree mac-addresses from the set built into the eprom on the switch chassis. Use the command "show sprom chassis" to show the list of mac-addresses.

5500 (enable) show sprom chassis

Serial EEPROM Contents:

EEPROM valid : 55aa

EEPROM version: 0

Serial Number : 129405064

H/W Version : 1.1

MAC Addresses : 00-e0-fe-de-7b-00 (through 00-e0-fe-de-7e-ff)

MAC Addr Size : 1024

Model String : WS-C5500

Chassis Type : 8 (13 Slot Switch)

HW Changes : 0000

Mfg Date : 04/18/1997

Engineer Use : 0

EEPROM checksum: a514

The first mac address in the list is used for VLAN 1 and the next for VLAN 2 and so on.

5500 (enable) show spantree 1

VLAN 1

Spanning tree enabled

Spanning tree type ieee

Designated Root 00-e0-fe-de-7b-00

Designated Root Priority 32768

Designated Root Cost 0

Designated Root Port 1/0

Root Max Age 20 sec Hello Time 2 sec Forward Delay 15 sec

Bridge ID MAC ADDR 00-e0-fe-de-7b-00

Bridge ID Priority 32768

Bridge Max Age 20 sec Hello Time 2 sec Forward Delay 15 sec

Mike

[snitram]

Hi Mike,

many thanks; this fully answers my question.

Best regatds, Martin

[milan.kulik]

Hi,

do you know the same secret for Cat4000, Cat6000, Cat2900/3500XL?

Thanks and regards,

Milan

[mtorelli]

Milan,

On a catalyst 6000 running in the hybrid mode, the command is the same as on the cat5000. On a catalyst 6000 running in the integrated IOS mode the command is "sh catalyst6000 chassis-mac-addresses".

For the cat4000 supervisor I (WS-X4012) and supervisor II (WS-X4013) these mac-addresses come from the supervisor module rather than from the chassis. So, you can get them from the show module command. Look at the mac-addresses associated with module 1. For the cat4000 supervisor III (WS-X4014) and supervisor IV (WS-X4015), you can get them from the command "show idprom chassis". Look at the output of MAC Base=.

Finally, for the Catalyst 2900XL/3500XL switches you can look at the output of "show version". Scroll down to where it reads Base Ethernet MAC-Address:

Mike