05-19-2009 10:50 AM - edited 03-06-2019 05:48 AM
I have a circular network loop using MST. The switches are connected via dual gigabit fiber in an etherchannel bundle.
I had to re-run fiber connecting 2 of the switches, so I shut down the port-channel interface between them. Now that I have all of the cabling back in place, will there be any interruption of service when I re-enable the etherchannel link?
I understand that MST touts speed as one of its key selling points, but this is an extremely high availability environment and even a few seconds of downtime could be catastrophic.
In my mind, it shouldn't be any different than how MST would operate if a cable were to be removed from a switch, which is something I've tested and worked perfectly. I just can't afford any gotchas here. UDLD is enabled on both switches; aside from that all relevant information should be below.
In short, here is a simple diagram.
A--------B
| |
D--------C
The port channel interface between switch A and D is administratively shut down. When I re-enable it, will it disrupt any traffic?
Here is my configuration:
A:
MST Config:
!
spanning-tree mst configuration
name CLV-Region
revision 10
instance 1 vlan 2-6, 15, 20-23, 30, 40, 50, 100, 200
!
spanning-tree mst 0-2 priority 8192
Interface config:
CLV-MDF-SW-01#sh run int gi1/16
Building configuration...
Current configuration : 311 bytes
!
interface GigabitEthernet1/16
description CLV-IDF2-SW-01 Uplink
switchport trunk encapsulation dot1q
switchport mode trunk
service-policy output autoqos-voip-policy
qos trust cos
auto qos voip trust
tx-queue 3
bandwidth percent 33
priority high
shape percent 33
channel-group 2 mode on
end
CLV-MDF-SW-01#sh run int gi1/17
Building configuration...
Current configuration : 311 bytes
!
interface GigabitEthernet1/17
description CLV-IDF2-SW-01 Uplink
switchport trunk encapsulation dot1q
switchport mode trunk
service-policy output autoqos-voip-policy
qos trust cos
auto qos voip trust
tx-queue 3
bandwidth percent 33
priority high
shape percent 33
channel-group 2 mode on
end
CLV-MDF-SW-01#sh run int po2
Building configuration...
Current configuration : 139 bytes
!
interface Port-channel2
description CLV-IDF2-SW-01 Uplink
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
end
D:
MST Config:
!
spanning-tree mode mst
spanning-tree loopguard default
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
!
spanning-tree mst configuration
name CLV-Region
revision 10
instance 1 vlan 2-6, 20-23, 30, 40, 100, 200
!
spanning-tree mst 0-2 priority 24576
Interface config:
!
interface GigabitEthernet0/1
description CLV-MDF-SW-01 Uplink
switchport trunk encapsulation dot1q
switchport mode trunk
shutdown
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
priority-queue out
mls qos trust cos
auto qos voip trust
channel-group 1 mode on
end
CLV-IDF2-SW-01#sh run int gi0/2
Building configuration...
Current configuration : 321 bytes
!
interface GigabitEthernet0/2
description CLV-MDF-SW-01 Uplink
switchport trunk encapsulation dot1q
switchport mode trunk
shutdown
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
queue-set 2
priority-queue out
mls qos trust cos
auto qos voip trust
channel-group 1 mode on
end
CLV-IDF2-SW-01#sh run int po1
Building configuration...
Current configuration : 102 bytes
!
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
shutdown
end
All in all it seems like a no brainer, but I'd rather someone with more MST experience comment on this. I've goofed before by adding a VLAN and causing an instance recalculation (outage!) and would rather not have to explain something like that again.
Thanks,
Jason
05-19-2009 12:33 PM
Hello Jason,
I don't know if it is an error on reporting but the two lists of vlans associated to mst 1 don't match:
you have the same region name, the same rev. number but I see
A:
instance 1 vlan 2-6, 15, 20-23, 30, 40, 50, 100, 200
D:
instance 1 vlan 2-6, 20-23, 30, 40, 100, 200
vlan 50 is missing here so if you connect them they will treat each other as belonging to a different MST region and using CST.
I think you need to make configurations identical before trying to connect them.
More probably it is just an editing error.
Hope to help
Giuseppe
05-19-2009 12:49 PM
It's not an editing error; I just haven't had a downtime window to add VLAN 50 to the rest of my switches. It hasn't been a problem with any of my other switches in the loop, so I'm assuming having the same instance name will suffice.
05-19-2009 01:26 PM
Hello Jason,
as far as I know it is not enough because the MST BPDU contains a special hash calculated using the vlan to instances mapping.
if the hash values don't match the switches think they are in different MST region.
You have two MST regions already.
see
MST-enabled switches only form an MST region if they have a matching VLAN-to-IST mapping, MST configuration name, and MST revision. If any of these three fails, the port will be flagged as a boundary port.
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094366.shtml
Hope to help
Giuseppe
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