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ARP entry / No MAC entry


Would appreciate very much if somebody could help me understand this!

Had a problem where 2 printers were on the same subnet and vlan. One printer responded to ping from the Layer 3 core switch on the LAN. The other printer did not. Thats not the weird thing (it seems printer's default gateway was not correctly configured).

What I found hard to understand is that the non-working printer had a fresh ARP entry on the Layer3 switch BUT NO MAC TABLE ENTRY.

What I don't understand is how the layer 3 switch could learn the printer's IP-->MAC mapping and yet not know which interface the MAC address hung off.

If the Layer3 switch is receiving a reply to its ARP requests then it is therefore receiving frames from the printer, so how could it not have added an entry to its MAC table?

With the printer that was responding to pings, there was both an ARP entry AND a MAC table entry on the Layer3 switch.

Please help me, this is really doing my head in....

Any suggestions appreciated.


  • Other Network Infrastructure Subjects

Re: ARP entry / No MAC entry


you could have different timers for CAM table and ARP table. So CAM could forget entries quicker than ARP.

Hope this helps! Please rate all posts.