I have a 4-switch stack of Alcatel Omniswitches connected to an HP 5412 core via 8 uplinks; these are ports D11-D18. Unfortunately, the client did not yet give me access to the Alcatels, but a request has been sent out. Meanwhile, I am seeing a high amount of TX/RX traffic on several ports in IMC regarding the core. An example: enter image description here

In past experience, this is generally indicative of a loop of some sort. (Note: This is a school, and students have been known to intentionally plug in an Ethernet cord from one wall to another. We have plans to re-mediate this, believe me.)

The setup is rather simplistic in that there are a total of 324 Cisco WAPs, each connected to one of the four switches in the Alcatel stack with a 1 Gbit uplink. Now, on the core, when I run:

show lldp info remote-devices D11

(for each port. I did it one by one instead of a range to specify).

Each port from D11-D17 shows the MAC address of the Alcatel stack as well as the port to which it is connected in a fashing like:

PortId       : 2024 // Switch #2 port 24

and so on. On port D18, however, the last port in the LAG, I see every single WAP. This is the case with both CDP and LLDP:

enter image description here

Is this normal behavior?

  • I guess port D18 would be connected to port 3024 of the Alcatel stack, but maybe there is some misconfiguration for port D18 in the HP core? Can you also show the spanning tree configuration and status of those interfaces? – xpto Feb 5 '16 at 2:39
  • In my opinion, device connected in D18 port is acting like a L1 device. I mean, in a normal Switching infraestructure you should only see ONE lldp device per port. Maybe, D11-D17 are not forming a part of the lag and they are blocked by STP but it just guessing. We need a show stp and show interfaces status for HP an Alcatel devices. – KorXo Feb 5 '16 at 18:22
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 10 '17 at 2:58

Firstly, it does look very much like you have had a broadcast/multicast storm and an external loop would do it. So, some sort of mitigation with spanning tree, loop protection, multicast rate limiting sounds like a plan.

With LLDP, the packets are sent to addresses in the IEEE reserved multicast range, which should not be forwarded by an intermediate switch. So, in a switched network you should only see direct neighbours. With CDP, the announcements are sent to a multicast address in Cisco's range, which by default will be forwarded. So seeing multiple CDP devices on one port is normal in a multivendor environment.

Your problem is that you are assuming that when you type show lldp info it shows LLDP information. Actually, on the HP 5412, CDP and LLDP share a common database. You just see different views of it with show lldp info and show cdp.

When the LLDP information is derived from CDP announcements, it is usually less complete. So even on the short report, you have a column (Chassis-ID, I believe) missing on all ports except D14 and D15. If anything, the thing that puzzles me is why you have only 2 LLDP entries and not 8. Certainly the behaviour on port D18 is expected, if slightly quirky.

TL;DR Turn off the CDP receiver or mentally filter what show lldp tells you on Procurve.

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