Annotated edit history of
Layer3Switching version 5, including all changes.
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AristotlePagaltzis |
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A layer 3 switch makes packet switching (forwarding) decisions based on both layer 3 addressing as well as layer 2 packet switching (forwarding) decisions. |
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LindsayDruett |
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AristotlePagaltzis |
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A very common mistake is that layer 3 switch functions are often compared with the functions of a router. A layer 3 switch is not a multi-port router. There are fundamental differences between the two: |
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LindsayDruett |
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AristotlePagaltzis |
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; __Packet switching (forwarding) decisions__ : A router only makes decisions at layer 3, whereas a layer 3 switch makes them at both layer 2 and layer 3. |
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; %%% __VTP (vLAN Trunking Protocol)__ : A router does not support this. It may have a [NIC] with 802.1q or ISL support, but only acts as an endpoint. |
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; %%% __Interfaces__ : On a router they are seen as router interfaces, apart from creating bridge groups. A layer 3 switch routes packets between vLANs (and the vLANs are seen as router interfaces), the switchports are either 802.1q or ISL trunk ports, or belong to a particular vLAN (either statically assigned, or dynmically assigned using 802.1x). |
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LindsayDruett |
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AristotlePagaltzis |
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Note that [Cisco] layer 3 switches like a [Cisco] Catalyst 3550 or 3750 series can be configured as multi-port routers, pure layer 3 switches, or hybrid router/layer 3 switches. When you get to [Cisco] Catalyst 4000 series and upwards, those switches are referred to as multi-layer switches, as they traditionally have separate routing and switching processors. These days, we are looking at each line card having its own switching processor (called dCEF (distributed [Cisco] Express Forwarding) modules in the [Cisco] world; aCEF (accelerated CEF) modules use the switching processor on the supervisor card). |
