Ethernet address on two trunked switches at the same time
I have two access layer switches sharing a dot1q trunk ( a port channel with four members), and an HP blade server with one connection (a port channel with two members) into each.. The blade server's connections into each switch is also a dot1q trunk tagging just one vlan. In each connection from the blade server to each switch the mac addresses look very much alike. I determine this by writing a script to log into both switches at once and run the "show mac add int" command on each port channel to the blade server. In tcpdumps the commands are sent typically about .1 - .4 seconds apart on average.
So if the "show mac addr int" command is being run .1 - .4 seconds apart on each switch and have a number of mac addresses in common, would this indicate that these ethernet addresses are flapping in a way that might cause interruptions in packet delivery? Some are experiencing missed pings. No VPCs are used in this configuration - just a pair of either 6509 or 7018 switches connected via a dot1q port channel.
It sounds to me like what you are trying to achieve is network teaming on the HP Blade Server whereby you can have a connection to two different switches.
Natively something like this would cause problems because both switchports (or portchannels) would see the same L2 Address which would then confuse upstream switches as they would not know where to forward frames to. I believe the HP servers may allow this type of setup but it requires a specific config on the teaming element to prevent a single MAC address being shown on two different ports.
I believe this is causing problems, and our group doesn't currently support it and I'm waiting to find out from the vendor if they're attempting it. My question is whether or not the output of a "show mac addr int" issued on the two switches a few tenths of a second apart is a sufficient indicator of a mac address being on two trunked switches at once, something I don't think should work.
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