OS6200 flat and AOS 1x1 STP mode

[nikolami]

Please, I need a help to clarify following situation. It is regarding OS6200 & AOS switches and STP.

OS6200 switch is connected only with one link to AOS switch. But between core AOS switches exist loop. Is it mandatory to configure flat STP on all switches (since OS6200 supports only flat STP)?
It will be convenient for services in network that we have 1x1 STP between core AOS switches, and to have flat STP just on OS6200. In case when only flat STP is implemented on all devices, blocked STP port is blocked for all VLANs (which limits flexibility for network traffic).

Small network diagram.




What will happen if OS6200 accidently connects to 2 AOS switches (there is a loop). Does OS6200 STP detects this loop and put one uplink port in blocked state? It is important that link between AOS core switches are not blocked. AOS switches have lower STP priority, but only configured per VLAN (I suppose that OS6200’s flat STP will not understand bridge priority per VLAN)?

In this situation is it mandatory to configure MST or flat STP on all switches?

Regards,
nikolami

[silvio]

Is it mandatory to configure flat STP on all switches (since OS6200 supports only flat STP)?

No, it's not mandatory. Between The AOS and LS6200 the BPDU for vlan 1 (=cist) will be used, if you have 1x1 at AOS.
But I prefer a homogenous structure - all the same stp at all switches (f.e. rstp with flat).

I suppose that OS6200’s flat STP will not understand bridge priority per VLAN?

right

Why do you haven't all vlans at all links? Now you haven't any redundance. If one link is broken vlan 1/2 or 3/4 will be lost. Better is to have all vlans at all links.
If you have enought lines/ports you can build LACP between the 9000's for more bw and more redundance.

If you wish load balancing (vlan1+2 via left link and vlan 3+4 at the right one) than you need 1x1 with different priorities for vlan 1/2 and 3/4. But for same STP is better to use MSTP.
Also a good way for load balancing between your 9000s is to use routing instead STP. With OSPF you have the possibility for ECMP. Than you haven't any trouble with your 6200.
regards Silvio

[nikolami]

Why do you haven't all vlans at all links? Now you haven't any redundance. If one link is broken vlan 1/2 or 3/4 will be lost. Better is to have all vlans at all links.
If you have enought lines/ports you can build LACP between the 9000's for more bw and more redundance.

Silvio, I agree with you. If 1x1 STP is used between OS9000 AOS switches then on all links between them should be configured all VLANs. Different bridge priorities per VLAN will perform load balancing between links. In practice, links from one switch to 2 others usually uses the same optic cable. Breaking one link in most cases means that both links from one switch are down. And usually these 2 links uses ports on the same NI module of switch. Of course, 2 links offer flexibility for configuration (e.g. load balancing)-

If you wish load balancing (vlan1+2 via left link and vlan 3+4 at the right one) than you need 1x1 with different priorities for vlan 1/2 and 3/4. But for same STP is better to use MSTP.
Also a good way for load balancing between your 9000s is to use routing instead STP. With OSPF you have the possibility for ECMP. Than you haven't any trouble with your 6200.

Yes, my main dilemma is to use or not MSTP. For now access switches are connected only with one link to core OS9000 switches. So there is no loop between OS6200 and core AOS switches. Problem will be if someone accidently connects one access OS6200 switch to 2 AOS switches OS9000. It will produce loop, and I'm not sure does STP will block link between AOS switches (it should be prevented). In case of using flat STP on OS6200 and 1x1 STP on OS9000, 1x1 priority is not valid, and MAC address of switch will have main role in deciding which switch is root bridge and what port will be blocked (on non-route bridge switch)?!

Since on all 3 OS9000 switches are connected access switches with same VLANs, I think that it will be easier to do L2 design, towards central router / L3 switch. Thank you for idea for routing.

Regards,
Nikolami

[silvio]

In case of using flat STP on OS6200 and 1x1 STP on OS9000, 1x1 priority is not valid, and MAC address of switch will have main role in deciding which switch is root bridge and what port will be blocked (on non-route bridge switch)?!

no, if you configure 1x1 so you configure priority per vlan. So also for vlan 1 (=cist). And this priority will be used for interworking with other switches with flat STP.
regards
Silvio

[nikolami]

Thank you Silvio.

no, if you configure 1x1 so you configure priority per vlan. So also for vlan 1 (=cist). And this priority will be used for interworking with other switches with flat STP.
regards
Silvio

I tested simple scenario - 1 AOS switch and 1 OS6200. On AOS switch is configured 1x1 STP with different bridge priorities for every VLAN (VLAN 1 - 10, VLAN 2 - 20 and VLAN 3 - 30). In begging, OS6200 see root bridge with priority 10.
After that I changed native VLAN on OS6200 trunk port to AOS switch from VLAN 1 to VLAN 2. Of course, on side of AOS switch default VLAN on port to OS6200 is changed from default VLAN 1 to VLAN 2. After that, OS6200 see root bridge with priority 20.

So STP exchange BPDUs over untagged VLAN, and OS6200 switch with flat STP, will see root bridge with priority of untagged VLAN from AOS switch.

regards,

nikolami

[silvio]

thanks for this info/tests .... I didn't know this. But if the behavior is like you have descripted than you'r right that the untagged (native) BPDU will be used from the 6200. That solidifies my opinion to use all the same STP in all the network.
regards Silvio

[nikolami]

Since OS6200 is cisco-like, I think that the following description for Cisco switches is valid for OS6200.

"When a Dot1q VLAN is configured on an interface, a default VLAN 1 is automatically created to process the CST. The default VLAN 1 created is only used for processing spanning tree BPDU packets. Even though these packets are Dot1q untagged, no other untagged data packet will be processed by this VLAN 1. Instead, all of the untagged data packet will be processed by the explicitly defined Native VLAN. If, however, no Native VLAN is defined, VLAN 1 will become the default the Native VLAN 1 (it can also be explicitly defined as Native VLAN 1) to handle all the untagged packets, including CST BPDUs and data packets."

This brings up my old dilemma, what is a diferrence between default and native VLAN
I think that native VLAN is used for carring untagged traffic over trunk link. Default VLAN is used for protocol's packets (STP, CDP, VTP) on Cisco switch.

AOS switches don't have native VLAN for untagged traffic, but uses default VLAN. So for exchanging BPDU packets, must be native VLAN on trunk port on OS6200 be the same as default VLAN on AOS tagged port.

From AOS Network Configuration Guide:
"Native VLAN and OmniSwitch Default VLAN Cisco uses the standard IEEE BPDU format for the native VLAN (i.e., VLAN 1 by default) over an
802.1Q trunk. Thus, by default the Common Spanning Tree (CST) instance of the native VLAN 1 for all Cisco switches and the STP instance for a port's default VLAN on an OmniSwitch will interoperate and successfully create a loop-free topology."

[cedric1]

So you resume all here.

So the best for you is to make a lab with MSTP, and configure some MSTI to make your link effective as with 1*1.

vlan 10, 20 msti 1
vlan 30, 40 msti 2

share root role for each msti

tag all vlans on all links, so in case of link falure traffic will continu to flow.

There is some techtips for 6200 mstp config with 9000.

make the design simple as possible and it will work perfectly (ask Silvio if it is not working ...)
check in knowledgbase

google eservice alcatel-lucent

[cedric1]

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