BPDU Inconsistencies with different vendors

[JohnTylerPearce]

Hey Guys,

I've been trying to fully understand the concept for the whole day. I ended up reading a very good article on INE about this same subject, but just wanted to make sure I understand the theory behind it.

Let's say I have 60 switches in a FLAT vlan enviornment, with a mixed switch enviornment of around 5 Brocade switches. Now, lets say the brocade switches are running RSTP while the other switches are all Cisco switches running RPVST+ .

The connects between the switcehs are access ports and not trunk ports. So from my understanding, the Cisco switches are going to be sending out BPDUs out of it's native vlan untagged, on destination MAC Address of (0180.c200.0000) which from my understanding is the IEEE STP standard. Now, I'm assuming that the Brocade switches would send out the IEEE standard, since it's native vlan is 1 as well, to (0180.c200.0000). I'm assuming in this instance, the connectivity should no really have any issues with BPDU-incompatibility.

Now, what if some of these Brocade switches were installed, with some Cisco switches that have ports configured to go to the brocade switches on access ports. So the Cisco switches like I said above are running RPVST+,  and since they are configured as 802.1q, and on the native vlan as well, I"m assuming they will send out the following BPDUs to the destination MAC addresses.

- (0180.c200.0000)

- (0100.0ccc.cccd)

I'm assuming the Brocade will not understand this RPVST+ (Really PVST+) BPDU, and would treat it as a multicast, and forward it out all ports except the one it was received on. Now, the brocade, I would assume would send the IEEE STP BPDU Destination MAC of (0180.c200.0000).

Do I have that whole Destination MAC theory down?

Also what types of issues would you expect to see from this kind of setup?           

[daniel.dib · Accepted solution]

I believe you have the theory down. Some potential issues:

• Slower convergence for non VLAN 1 VLANs
• Potential for bridging loops if VLAN 1 is not allowed on trunk

Do you have the option of running MST?

There is a document attached to this thread that was written for Cisco - Dell compatibility, but the theory should be the same.

https://supportforums.cisco.com/thread/2078934

Daniel Dib
CCIE #37149

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[JohnTylerPearce]

Daniel,

I know the backbone of MST, so to speak, is RSTP. But I"m assuming that's no RPVST+ obviously, just your standard RSTP. So I would assume a switch configured for MST, would send out BPDUs on Destination MAC Address of (0180.c200.000), whether its an access port or trunk port?

I plan on reading that thread a little later today, thanks for linking it.

[daniel.dib]

Yes, that is correct. BPDU is sent via the CIST untagged to the mentioned destination MAC address.

Here is a sample packet capture for you:

http://packetlife.net/captures/MSTP_Intra-Region_BPDUs.cap

Daniel Dib
CCIE #37149

Please rate helpful posts.

[JohnTylerPearce]

Daniel,

Thanks for the help and the link. They were all very helpful,