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New Member

Gigastack redundant link

I have GigaStack'ed a 3550 a 3524 and a 3548 together with 3 cables.

I need to set the 3524 Gigastack link 2 as redundant link , but there is

a specific command to do it ? How it decides which is the redundant link ?

I believe its cause of the mac address , the higher one is redundant .

I've also tried to set on the 3550 GigabitEthernet0/2 mac as "0004.b7cf.dc9a"

but the bia do not change , mac address is 0004.b7cf.dc9a

(bia 000a.b7cf.dc9a), so the redundant link.

Please help .

Regards,

Patrizio

3550: is spanning tree primary master

c3550-i9q3l2-mz.121-13.EA1.bin

GigabitEthernet0/2 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 000a.b7cf.dc9a (bia 000a.b7cf.dc9a)

Description: Gigastack Trunk

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Half-duplex, 1000Mb/s

Link type is autonegotiation, media type is CX Gigastack

output flow-control is off, input flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

GigaStack module(0.2) in GBIC slot. link1 is up, link2 is redundant link

3524: is spanning tree secondary master

c3500xl-c3h2s-mz.120-5.WC7.bin

GigabitEthernet0/2 is up, line protocol is up

Hardware is Gigabit Ethernet, address is 0005.9bcb.b59a (bia 0005.9bcb.b59a)

Description: Gigastack Trunk

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Auto-duplex (Half), 1000Mb/s, media type is CX_GIGASTACK

output flow-control is off, input flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

GigaStack module(0.2) in GBIC slot. link1 is up, link2 is up

3548: is spanning tree tertiary master

c3500xl-c3h2s-mz.120-5.WC7.bin

GigabitEthernet0/2 is up, line protocol is up

Hardware is Gigabit Ethernet, address is 0006.285b.2a72 (bia 0006.285b.2a72)

Description: Gigastack Trunk

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Auto-duplex (Half), 1000Mb/s, media type is CX_GIGASTACK

output flow-control is off, input flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

GigaStack module(0.2) in GBIC slot. link1 is up, link2 is up

8 REPLIES

Re: Gigastack redundant link

Hi,

use

spanning-tree priority ....

config command to define STP root in your network (the lowes number is the winner)

and

int ....

spanning-tree vlan ... cost .....

to determine the redundant line.

See http://www.cisco.com/warp/public/473/5.pdf for details.

Regards,

Milan

New Member

Re: Gigastack redundant link

Hi,

i've already configured STP and the relative redundant line.

The problem is that link 2 is made redundant by the loop breaking

algorithm , see http://www.cisco.com/warp/public/473/150.html for details.

The loop breaking algorithm occurs between the GigaStack GBICs by exchanging

MAC addresses using their A- and B-ports. The winner of the election will

become the master loop breaker and disable its port 2. The winner of the

election is the one with the lowest byte-order reversed MAC address.

If a gig port has the MAC address 00:d0:79:6b:ee:01, the the byte-order

reversed MAC address is 01:EE:6b:79:d0:00.

But even if I change the mac address does not work , maybe you have to reload all the switch after .

Regards,

Patrizio

Re: Gigastack redundant link

Hi Patrizio,

the "loop breaking algorithm" is something new for me. I've always thought the only STP was involved in loop breaking.

But if you read carefully the last paragraph of the material you mentioned (http://www.cisco.com/warp/public/473/150.html) there is:

"To find out which switch will disable its B-port, issue the sh int gig x/y command on each switch and make note of the MAC address IN PARENTHESIS (the one that says BIA and then a MAC address). With this information, perform the byte-order reversing operation and then compare them to find the smallest one. The smallest one will be the master loop breaker and will disable it's port 2."

So it says the bia (burnt-in-address) MAC address is used. Changing the port MAC address won't help you.

I think that if you want the B-port of another switch to get blocked the only way is to move the stacking GBIC from one switch to the other. To be clear:

If your switches are A, B, C and the B-port on switch C is being blocked now and you want the B-port on switch A to get blocked, swap the stacking GBICs between switches C and A.

Regards,

Milan

New Member

Re: Gigastack redundant link

Hi Milan,

i was wondering what BIA means , thank you for the explanations , but if isee the switch all the MAC are inherited from the switch itself.

Hardware is Gigabit Ethernet 0/2, address is 000a.b7cf.dc9a (bia 000a.b7cf.dc9a)

Hardware is Gigabit Ethernet 0/1, address is 000a.b7cf.dc99 (bia 000a.b7cf.dc99)

Hardware is Fast Ethernet 0/1 , address is 000a.b7cf.dc81 (bia 000a.b7cf.dc81)

Base ethernet MAC Address: 00:0A:B7:CF:DC:80

Should I change the MAC of the switch?

There is any way to see the MAC of the GBIC ?

Regards,

Patrizio

Re: Gigastack redundant link

Hi,

it really seems that the "bia" addresses are all inherited from the base MAC address nad there is no GBIC MAC address.

So I would try to change the base MAC address.

It's defined in env_var file on the flash.

It should be possible to change it by set MAC_ADDR command.

But I've never done it. It's probably necessary to do it in ROM mode.

Regards,

Milan

New Member

Re: Gigastack redundant link

Hi Milan,

but looking at the mac of the switch , if I've done right the reversed-order :

0005.9bcb.b580 3524

0006.285b.2a40 3548

000a.b7cf.dc80 3550

00:05:9B:CB:B5:80 3524

00:06:28:5B:2A:40 3548

00:0A:B7:CF:DC:80 3550

40:2A:5B:28:06:00 3548-reversed

80:B5:CB:9B:05:00 3524-reversed

80:DC:CF:B7:0A:00 3550-reversed

Should break the loop the 3548 , instead it break the loop the 3550 !

Regards,

Patrizio

Re: Gigastack redundant link

Patrizio,

the addresses you are considering are the base MAC addresses?

If yes, you should have used the interface MAC addresses!

So

3550: 000a.b7cf.dc9a

3524: 0005.9bcb.b59a

3548: 0006.285b.2a72

byte reversed:

3550: 9a:dc:cf:b7:0a:00

3524: 9a:b5:cb:9b:05:00

3548: 72:2a:5b:28:06:00

But still 3548 should be the winner.

It seems to me there is a mistake in the Master Loop Breaker algorithm description (the only one article on CCO) and that the highest byte-reversed address is the winner.

Regards,

Milan

New Member

Re: Gigastack redundant link

Hi Milan,

yes wrongly I've used the base MAC address , but I agree with you in both case the 3458 should be the winner , but as you see it wins the 3550 , higher win , a good question for Cisco about the Master Loop Breaker algorithm !

Thanks a lot.

Regards,

Patrizio

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