strange connectivity issue, symptom is "DUP!" pings

[tschaps]

Phasing in new HP network, chasing down issues. Mainly MSM430 APs, new 5406 Core switch with MSM765zl controller. Multiple VSC's and VLANs, but at this time, nothing access-controlled. The summary of what I've found: if an AP is plugged into certain ports on the 5406, after six minutes, any host connected on the main VSC loses IP connectivity but not the connection. They can ping other hosts on the LAN and WAN as usual, but every ping is returned with DUP! responses, and DNS lookups to the DC do not get a reply. Also, pinging the particular host from elsewhere on the LAN returns the same DUP! responses, starting at the same time (~six minutes) after association. Possibly relevant: the number of DUP! responses to each ping varies with the # of VSC bindings on the test AP. If I only have the main VSC active, everything works. Each additional VSC added adds one "DUP!" response after that six minute period, and again, same exact result pinging 'out' from affected host, or pinging affected hosts IP from elsewhere on the LAN. 

HERE's THE KICKER-- this only happens if the AP is plugged into a port on the lower row on the HP J9536A module. I have tried this dozens of times in the past few days, and this issue occurs only when the AP is plugged into ports B10, B12, B14, B16, or B18. Moving the AP to ports B9, B11, B13, B15, or B17 and this problem does not occur (and yes, the ports are configured identically). I know it sounds crazy, and I wouldn't believe it if I hadn't spent two days with a test AP, a test laptop, and running continuous pings both directions. I have reset the AP to factory defaults twice, but I can rule it out anyway, because this connectivity problem has been vexing me for months with the four APs I have in service plugged into this switch, and I finally noticed the pattern of connectivity issues, moved them all to "top row" ports and started testing with a backup MSM430, hopping ports and tracking behavior in each port. Now, I could fiddle around with VSC settings and radio settings, but I have 56 APs connected in other closets around the school configured the same, plugged into E2910z PoE switches and not having this issue. The difference here comes down to the ports on this 5406. And also, the logging on the AP is set to debug but shows nothing other than the handshakes and other EAPOL events. 

I am going to get in touch with HP about this, but the engineer who designed the network is coming out Monday to look at it. I wanted to run this by this forum to see if it rings a bell with anyone, if anyone's seen similar behavior or if the approximate 6-minute time period correlates to anything. All of you having connectivity issues, too, as seen in other threads here, please try some pinging to see if you get the DUP!'s.

Thanks

[Patrick R]

What is the chassis firmware and which module (V1 or V2).

[tschaps]

Image stamp: /sw/code/build/btm(K_15_06)
Oct 8 2011 17:39:18
K.15.06.0008
85
Boot Image: Primary

5406-1# show modules

Status and Counters - Module Information

Chassis: E5406zl J8697A! Serial Number: SG18Dxxxxx
Allow V1 Modules: Yes

Management Module: J8726A Serial Number: ID132xxxxx Core Dump: YES

Core Mod
Slot Module Description Serial Number Status Dump Ver
---- -------------------------------------- -------------- -------- ----- ---
A HP J9534A 24p Gig-T PoE+ v2 zl Module SG131xxxxx Up YES 2
B HP J9536A 20p GT PoE+/2p SFP+ v2 zl... SG132xxxxx Up YES 2
D HP J9154A Services zl Module SG131xxxxx Up NO 1
F HP J9537A 24p SFP v2 zl Module SG115xxxxx Up YES 2

Thanks, let me know if you need any more information.