Catalyst 9407 StackWise Virtual Multi-Chassis Ether Channel STP Loop

barkerh · ‎11-05-2018

Esteemed Cisco Community,

I have two identical Catalyst 9407s with IOS 16.9 Fuji. This IOS is the first to support StackWise Virtual (SWV) on the 9407 hardware. My licenses support SWV. I have taken my first foray into this marvelous new world, and now I am clueless at the prompt. My tale begins below.

What has been done already with success:

- Connection of two SVL ports between supervisors

- Programming of two SVL ports

- StackWise Virtual has been configured and is working

- Connection of two ports between Supervisors to be programmed as Multi-Chassis Etherchannel (MEC)

The MEC is intended to be used for the Dual-Active Detection (DAD) Links. I programmed them as individual ports previously (assuming this is the "Fast-Hello" method):

interface TenGigabitEthernet1/3/0/3
stackwise-virtual dual-active-detection

interface TenGigabitEthernet2/3/0/3
stackwise-virtual dual-active-detection

This all seems to work.

The problems begin when I attempt to configure the DAD links in a port channel. I am trying to configure it this way because the IOS-XE documentation indicates MEC with PAgP is the desired method for DAD under SWV.

So, I re-program and reload the switches and attempt to perform the following configuration:

interface range TenGigabitEthernet1/3/0/3,TenGigabitEthernet2/3/0/3
description stackwise-virtual dual-active-detection

channel-group 1 mode desirable

interface port-channel1

description Dual-Active-Detection PAgP MEC

shut

exit

stackwise-virtual
dual-active detection pagp
dual-active detection pagp trust channel-group 1

exit

interface port-channel1

no shut

Then I issue "show stackwise dual-active-detection pagp":

#show stackwise-virtual dual-active-detection pagp
Pagp dual-active detection enabled: Yes
In dual-active recovery mode: No

Channel group 1
Dual-Active Partner Partner Partner
Port Detect Capable Name Port Version
Te1/3/0/3 No None None N/A
Te2/3/0/3 No None None N/A

The port channel also shows down:

#show int po1
Port-channel1 is down, line protocol is down (notconnect)
Hardware is EtherChannel, address is 0000.0000.0000 (bia 0000.0000.0000)
Description: Dual-Active Detection MEC
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255

Looking at reasons that the etherchannel is down, I discover spanning-tree detected a loop and starts blocking VLAN 1:

#sh spanning-tree blockedports

Name Blocked Interfaces List
-------------------- ------------------------------------
VLAN0001 Te2/3/0/3, Te2/3/0/4

Number of blocked ports (segments) in the system : 2

I would expect this behavior since the switch sees itself as a single unit, so now a link between chassis is a loop. However, the sample configurations do not indicate anything about spanning-tree or loops, they just say to program it and it shall work.

What am I missing? I was under the impression the MEC was functionally similar to the vPC in NX-OS. I am not sure how to program a PAgP MEC between the two supervisors if the chassis sees it as a loop and starts blocking ports. Naturally, I desire to adhere to Cisco's recommended configuration.

What am I missing? I have followed the IOS-XE 16.9 Fuji instructions for Dual-Active-Detection using PAgP to the letter. Any suggestions are appreciated and welcome.

Thank you!!!!!!

balaji.bandi · ‎11-05-2018

Where is the domain Id configured, post the full configuration or follow below guide example :

http://nexp.com.ua/technologies/ios-xe/cat9k-stackwise-virtual/

BB

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barkerh · ‎11-05-2018

Hello Good Sir,

Thank you for the quick response, I apologize for being remiss.

Here is the stackwise-virtual configuration:

stackwise-virtual
domain 1
dual-active detection pagp trust channel-group

Cheers!

mateens · ‎11-06-2018

*the device should be rebooted for the configuration changes to take effect.

and according to documentation the config is done on one single interface.

mateens · ‎11-06-2018

SUMMARY STEPS
1. enable
2. configure terminal
3. interface TenGigabitEthernet interface
4. channel-group group_ID mode desirable
5. exit
6. interface port-channel channel-group-id
7. shutdown
8. exit
9. stackwise-virtual
10. dual-active detection pagp
11. dual-active detection pagp trust channel-group channel-group id
12. exit
13. interface port-channel portchannel
14. no shutdown
15. end
16. write memory
17. reload

barkerh · ‎11-06-2018

Hello again,

Thank you for your swift and informed responses.

I reloaded the switch after the changes. I have reloaded this stack more times than I have ever rebooted any Cisco product. :-)

So this is what I understand from the responses (thank you again!):

* Do not program the second interface on the second chassis' supervisor *

I backed out of all the config and started over. To recap:

I have a physical connection run between the two chassis supervisor blades (sup is in slot 3):

chassis 1: ten1/3/0/3 ----------- chassis 2: ten2/3/0/3

I then programmed only the first interface in the set:

interface TenGigabitEthernet1/3/0/3
description Dual-Active Detection MEC member
channel-group 1 mode desirable

exit

interface port-channel1

shut

exit

stackwise virtual

dual-active-detection pagp

dual-active-detection pagp trust channel-group 1

int po1

no shut

No configuration was entered on interface TenGigabitEthernet 2/3/0/3. I now have the following ("show stackwise-virtual dual-active-detection pagp"):

Channel group 1
Dual-Active Partner Partner Partner
Port Detect Capable Name Port Version
Te1/3/0/3 No None None N/A

And spanning-tree is still doing what it is designed to do:

Name Blocked Interfaces List
-------------------- ------------------------------------
VLAN0001 Te2/3/0/3

The MEC does not appear to work as advertised by the documentation.

I will have to move forward with the individual links programmed for DAD, as the switch does not appear to be able to distinguish between a DAD link and a regular link so it sees a loop and blocks the second interface. Perhaps I have missed some preliminary config prior to setting the two switches up as a stackwise-virtual pair. In any event, thank you to the Cisco Community for all of your help, perhaps this feature is still under development since this is the first IOS to support SWV in these devices. Thank you once again for all of your help!

mateens · ‎11-15-2018

dual-active detection using Enhanced PAgP has been implemented to assist in dual-active detection and is configured with the downlink facing peers not with the chassis # 2.