Exclude vlan from MSTAG

[Andreas Martensson]

Hi!

Is it possible to exclude a vlan from MSTAG?

I don't wan't to run spanning tree at all on this vlan. It seems like the only option is to change instance (all vlans are assigned by default to instance 0)?

As i recall MSTAG is still blocking a port somewhere along the access-ring, even if the vlan runs in a separate mstag instance.

I want to have a vlan that is not blocked along the accessring. The vlan does not need to run stp, since we never do bridgeing on the vlan.

And i still want to run MSTAG at the accesring.

Any ideas?

Regads

Andreas Martensson

[Alexei Kiritchenko]

Hello Andreas,

MST Access Gateway is not really running spanning tree. All it does is send pre-canned BPDU into access network at hello timer and snoop the TCN from access network, flush its local MAC address table and trigger VPLS MAC withdrawal accordingly.

You can find more details here:

ASR9000/XR Using MST-AG (MST Access Gateway), MST and VPLS

https://supportforums.cisco.com/docs/DOC-15963

ASR9k running MSTAG don’t block any ports. Those pre-canned BPDUs make the access switches to block their ports.

Configuring MSTAG you define which subinterfaces you want to enable it on,  do not include subinterfaces into MSTPAG config with those VLANs where you don’t want to run it on.

Regards,

/A

[Andreas Martensson]

Hi,

well i did not explain the situation thoroughly, and i realize this is probably not a MSTAG issue, but i give it a shot here anyway.

I have set up a complete MSTAG between two asr9k. The MSTAG is configured at one subinterface per asr9k.

The access swtiches (3560:s) does block a port according to the mst configuation of the switches witch is correct.

I create a new subinterface (vlan) at the asr:s, but the 3560s is blocking this vlan since vlan 1-4094 is configured as a part of the MST.

So, what do i do to not make the switches block this vlan.

I have tried to put the vlan in another MST instance without any luck. A have also tried to do 'no spanning-tree vlan x' at the switch, but without any luck. The 3560 is still blocking the vlan at the same port.

Config at the 3560:s

spanning-tree mode mst

!

spanning-tree mst configuration

name xxx

revision xx

instance 1 vlan 4094

!

sh spanning-tree blockedports

Name                 Blocked Interfaces List

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

MST0                 Gi0/8

MST1                 Gi0/8

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

I recon that it is the MST name and revision that globally connects the switch tho the MSTAG, thus blocking the vlan.

/Andreas

[Alexei Kiritchenko]

Hello Andreas,

From my basic LAN knowledge I know MST always runs Internal Spanning Tree (IST, instance 0). It always exists on ALL ports.

We cannot disable STP on a per vlan basis in MST. Actually, MST is not running per vlan. MST is calculating the topology for several instances, completely independently of the existence of any vlan. Vlans are then mapped to the instances as to the mst configuration.

You may ask LAN switching community gurus to clarify/confirm this.

Regards,

/A

[Sanjeev Rampal · Accepted solution]

Andreas

Take a look at the MSTAG edge mode.

http://www.cisco.com/en/US/docs/routers/asr9000/software/asr9k_r4.1/lxvpn/configuration/guide/lesc41mstp.html#wp1014085

You can put "L3 VLANs" into a separate MSTI and use this mode to ensure that this MSTI is always unblocked. This may address what you are looking for.

[Andreas Martensson]

Actually, this is just what i was looking for!

Thanx!

/Andreas