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What will happen If a switch received non Ethernet traffic


I need your advise please regarding below

What will happen If a switch received non Ethernet traffic ; lets say CLNS traffic

Will switch drop these packets or forward it to all ports ; i.e. same behavior for Ethernet traffic with unknown destinations ????

Appreciate your quick response

Many Thanks

Sherif Ismail

VIP Mentor

CLNS lives on a higher layer then Ethernet (it can be transported by Ethernet).

But back to your question: If it is something that is not Ethernet, then the switch can't recognize it and will discard it.

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Hello Sherif,

Non-Ethernet traffic would mean frames of a different type - Token Ring, HDLC, PPP, Frame Relay, ATM, LAPB, ... A frame that is not of an Ethernet type can be generated only by a network card that is itself of a different type. An Ethernet card is unable to send a non-Ethernet frame (at least a correctly working one). As each data link layer technology uses a different physical layer, even if you somehow managed to have, say, a Token Ring card connected to an Ethernet switch, they would not hear each other or just consider the signals coming from the opposite device as unintelligible gibberish. They would be totally unable to understand and process frames encoded into these signals.

So the differences in the physical layer would practically prevent any sensible communication of the two devices. But even if somehow the frames sent by one device could be read by the other, because of differences in the frame formats, none of the devices would be processing it correctly. It is highly likely that the Frame Check Sequence field (the checksum) is computed differently for different link layer technologies, and it may even be located in different places. Thus, a FCS field computed by one device would not match the FCS computed by the second device. Therefore, frames of a particular type would most probably be considered as corrupted frames by the second device, and they would be dropped.

In the highly unlikely event that the frames would be accepted and the FCS was somehow correct even though the entire frame is of a different type, the receiving device would not be able to tell the difference, and it would simply try to process the frame as if it was a frame it understands. What could happen now is a pure speculation - virtually anything that can happen to a frame during switching operation (dropping, switching out a particular port, flooding).

Karsten is very correct - the CLNP is a network layer protocol and is inserted into Ethernet frames. Hence, using CLNP does not change the Ethernet frame type, and an Ethernet frame carrying a CLNP packet would be switched through a switch just like any other frame, based on its destination MAC address.

Best regards,




Many thanks for your excellent reply .. much appreciated

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