I know the CAM table in a switch holds MAC addresses and the ports that are associated with the respective MAC addresses. There are no such thing as CAM addresses from my knowledge, so why is it called CAM table and not MAC table?
Switch – Why is the CAM table in a switch called CAM table and not MAC table even though it holds MAC addresses
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Good question. I'll answer it with an animation:
When Host A sends the frame, the switch does not have anything in its MAC address table. Upon receiving the frame, it records Host A's MAC Address to Switch Port mapping. Since it doesn't know where the destination MAC address is, it floods the frame out all ports.
This assures that if host B exists (which at this point, the switch does not know yet), that it will receive it. Hopefully, upon receiving the frame, Host B will generate a response frame, which will allow the Switch to learn the MAC address mapping from the return frame.
You can read more about how a Switch works here (where I took the animation from). I would also suggest reading the entire article series for a closer look at how a packet moves through a network.
One last note regarding the terms Flooding vs Broadcast. A switch never broadcasts frames, a broadcast is not an action a switch can take. A switch can only flood a frame. A broadcast is simply a frame with a destination MAC address of ffff.ffff.ffff. This is often confused because the end effect is the same, but they are actually different.
- The MAC address table relates the source MAC addresses for frames which have come into a port with the port. This lets the switch know to which port it should send frames with that destination MAC address. The MAC addresses are from hosts connected to the ports. The CPU port is the switch itself.
- Static MAC addresses in the MAC address table were manually configured. The dynamic entries in the MAC address table will time out after a while. The table is dynamic and when a frame with a source MAC address comes into a switch the table is updated to reflect that the device with that MAC address is out that port. There can only be a single port for a MAC address. Manually putting an entry in the table bypasses all of that. The switch will automtically have static entries for itself.
- Only allowing traffic destined to a MAC address through a manually configured port will help prevent ARP spoofing problems.
- You can have frames from many different hosts (MAC addresses) come into a single port. This is the case when a hub or switch with many hosts is connected to a switch port.
Best Answer
CAM (Content Addressable Memory) is memory that can be addressed by content, rather than a numeric memory address. You can look up the interface by presenting the memory with the MAC address. This is done in a single CPU cycle vs. the traditional programming of searching through a table, which will cost many CPU cycles.
There is also TCAM (Ternary Content Addressable Memory) that can use a mask. This is particularly useful for IP addressing, and it is used by ACLs or routing tables, among other things.
CAM and TCAM cost much more than standard DRAM, but the performance boost given by them for specific applications can be worth the cost, power, and size compromises you must make.
Since most standard PCs do not include anything like this, you can see how a purpose-built piece of hardware, e.g. router or switch, can have a performance advantage over a standard PC for the purpose of routing or switching.