hi every body!
I am a bit confused about thses terms.
For example when we say layer 3 device, that means it can understand upto layer 3 information, anything beyond layer 3 is greek for layer 3 device.
But then we find layer 3 device , for example router using access list to filter, or identify the traffic based on ports.
My question being layer 3 device, router should not be able to identify or filter the traffic based on ports,(udp or tcp),as there are above layer 3 and thus be greek to router. But this is not the case in realty.Similarly, we find layer 2 switch filtering traffic based on ip addresses. Again being layer 2 , switch device should not be able to do that as ip address is in layer 3.
Does anyone care to elaborate on that?
thanks a lot and have a nice day!
Wow, what a coincidence. I just asked a similar question regrding L2 switches with QoS configs on them that use L3/L4 ACLs to match traffic.
Go to the this thread and read it; I think it will help you.
It's a general label used to describe the major functionality of the device.
As technology develops, features are added.
In the "good old days," a Layer two switch was truly just a fast, multi-port bridge. As the technology evolved, feature were added to address the needs of a larger network (enabled by the base technology, like switching).
For layer 2, some of the features added later were for things like multicast control (cgmp, igmp), flood/broadcast control, ACL capability, multi-link ...
Same thing for routers at layer 3. As new technologies emerged, and network diameters grew, features were developed and integrated beyond the base functionality (like PIM, HSRP/VRRP, tunneling ...)
So, some of the labeling is just legacy notation, some is describing a class of device, that by description gives a general indication of where it might fit within the larger network.
A layer 3 switch, by basic function is a fast multi-port router ... but the additional functionality usually added to the L3 switch and/or the broader classes of interfaces generally available to a router distinguish them as separate classes of device, and describe different roles within a typical network.