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unicast traffic from other ports

eelarry
Occasional Contributor

unicast traffic from other ports

Hi,

I'm looking at Wireshark captures from an HP 1800 with older firmware.

What I'm seeing violates the expected behavior of a switch port, that the only traffic a switch port should see besides unicast traffic to/from the host on that port is broadcast, multicast, or unknown unicast.

Has anyone else seen this behavior on an HP switch with old firmware? Thanks.
4 REPLIES
Pieter 't Hart
Honored Contributor

Re: unicast traffic from other ports

>>> What I'm seeing violates the expected behavior of a switch port, that the only traffic a switch port should see besides unicast traffic to/from the host on that port is broadcast, multicast, or unknown unicast.<<<

I think your view of "excpected behaviour" is in error.
What's your interpretation of broadcast traffic?

Broad cast traffic is destined to ALL destinations.
Only the receiving end knows it doesn't want this traffic. The switch can't!
So the switch MUST(/can only) forward this to all connected ports.

That's why broadcast traffic is a potential problem on a (large) network.
Vlan's can be used to decrease broadcast traffic. when using vlan's broadcast traffic is sent to all ports only within ports that are member of this vlan.

Similar goes for multicast (just call it broadcast within a subnet).
eelarry
Occasional Contributor

Re: unicast traffic from other ports

What I said was in my original statement was:

the only traffic a switch port should see besides unicast traffic to/from the host on that port is *broadcast*, *multicast*, or *unknown unicast*.

Your reply doesn't acknowledge having read that statement.
Pieter 't Hart
Honored Contributor

Re: unicast traffic from other ports

yes you're right, i didn't read the post right.

But then what is your question?
what unexpected traffic do you see in your capture?

Maybe these are non-tcp/ip packets?
Other protocols may send packets not falling in the cattegories multicast, or unknown unicast
eelarry
Occasional Contributor

Re: unicast traffic from other ports

Admittedly, at the time, I was fishing for answers, and I finally found it: this result was created by a virtual multicast mac address from a Microsoft load balancer.