STP on MSM466 devices

[ciscoworlds]

Hi. I'm working on a topology in which we want to use a wireless link with two MSM466-R devices as backup. I want to know that if these devices act like a L2 switch and send/receive STP BPDUs. I saw the STP option, but I'm not sure about the options that are available regarding STP. actually I want to change the STP port cost on these devices to make them to select the wireless link as root port. in my topology and after establishing second link, the wireless link that was up before, becomes "Locked" and from my veiwpoint, it is locked by STP to prevent loops. but after the priomary wired links goes down, the wireless link don't come up automatically. my topology is attached to post. tnx a lot.

[Peter_Debruyne]

Hi,

In general the STP implementation on MSM is not very advanced, so I prefer to use a classic network device behind the AP mesh to perform the L2 functions, this means no STP on the APs (they should transport STP packets as data packets over the mesh link).

Depending on the devices used you should be able to use:

* xSTP: run direct xSTP between the 3800 and backbone switch. This will give you the path cost tuning option on the 3800.

* LACP: put the 2 links in a link-agg, configure the mesh AP link to 100Mbps , wired connection to 1Gbps. LACP will select the link with highest speed and revert to other link if main link is down. Use LACP short timers for faster detection (default LACP is 30s hello)

* if device supports ethernet OAM ( not on provision, but available on comware): use OAM for fast link failure detection. Can be useful if 2 meshed links are used in a link-agg (done by the switches) and fast link failure is required.

HTH, best regards,Peter

[ciscoworlds]

Hi. tnanks for your reply. can I configure MSM466-R APs to act like a bridge in order to completely eliminate their effect on STP? if this is the case, our scenario gets simpler solution.

and another point is that, as I know, with many vendors, like Cisco and extreme (Enterasys), that the ports participate in etherchannel (LACP) just when they share some common parameters that Speed, Duplex, STP cost, VLANS allowed to trasfer, etc among physical ports. 

[Peter_Debruyne]

Hi,

* when stp is not enabled on the AP, it should act as a transparent 'hub' from STP point of view, resulting in the 2 switches seeing each other as STP peers.

* You are correct on the LACP rules (except STP cost, STP runs on the link-agg parent interface, not on the member ports), so in case you set the switch to AP link to 100Mb, LACP would leave that port unselected (not used), since a better port (the direct Gigabit link) is available. When the direct Gigabit link fails however, the 100Mb link is the only remaining candidate, so LACP would set it to selected.

Other parameters (vlans etc) must be set equally on all member ports of course.

HTH,Peter