SG500 showing the same MAC address on more than one port?

[danielj80]

My ISP has been helping me troubleshoot a problem we've been having with an interaction between our SG500 stack on their HP customer premises equipment.

I have the SG500 stack partitioned into two VLANS. 8 ports on VLAN11, and the rest on VLAN1. Both are native, untagged VLANs so they should only carry traffic for their own VLAN with no mixing. I also route between these VLANs on the stack.

VLAN11 switch ip: 10.76.20.20

VLAN1 switch ip: 10.1.1.1

I've taken a port from each VLAN, and plugged it into the ISP's HP switch, where there are matching separated VLANs which then connect to a remote datacenter through a MPLS.

Here's the issue: the SG500 seems to be presenting the base mac address on both ports of the ISP's HP switch. This confuses the HP switch, and I end up having packets drop into a black hole. This is the output from the HP switch showing the SG500 stack's base mac moving between ports within a few seconds:

HP# show mac-address 8843e1-af7085

Status and Counters - Address Table - 8843e1-af7085

  MAC Address : 8843e1-af7085

  Located on Port : 15

HP# show mac-address 8843e1-af7085

Status and Counters - Address Table - 8843e1-af7085

  MAC Address : 8843e1-af7085
  Located on Port : 11

Any idea what is going on here? It's as if the SG500 is using the same MAC for both its IP addresses.

Thanks!

[Tom Watts · Accepted solution]

Hi Dani, the only MAC address advertised by the SX300/500 series should be the system MAC. If you do show mac address-table on the SX500 you should see the same MAC for both VLAN. I do not know why this is confusing the HP switch unless it is not handling the tag vlan correctly between switches.

-Tom
Please mark answered for helpful posts

[danielj80]

Tom,

Indeed, the HP switch was not indexing on MAC and VLAN properly. The ISP replaced the switch with a one from Juniper, and the problem went away.

[ZaidShaikh]

Hi guys,

i am trying to find the IP add associated to mac on cisco sg500 switch port. i am performing these to

#sh mac address-table interface GigabitEthernet1/1
Aging time is 300 sec

Vlan Mac Address Port Type
-------- --------------------- ---------- ----------
1 34:64:a9:10:d6:16 gi1/1/1 dynamic

#sh arp mac-address 34:64:a9:10:d6:16

Total number of entries: 1

VLAN Interface IP address HW address status
--------------------- --------------- ------------------- ---------------

There is no entry showing in it. Can anyone guide me