Differences between current version and previous revision of Layer3Switching.
Other diffs: Previous Major Revision, Previous Author, or view the Annotated Edit History
| Newer page: | version 5 | Last edited on Wednesday, March 24, 2004 6:23:07 am | by AristotlePagaltzis | |
| Older page: | version 4 | Last edited on Wednesday, March 10, 2004 3:55:50 pm | by DavidHallett | Revert |
@@ -1,19 +1,9 @@
-A layer 3 switch also
makes packet switching (forwarding) decisions based on Layer
3 Addressing
as well as layer 2 packet switching (forwarding) decisions. A very common mistake is the layer 3 switch's function is often compared with the functions of a router
.
+A layer 3 switch makes packet switching (forwarding) decisions based on both layer
3 addressing
as well as layer 2 packet switching (forwarding) decisions.
-There
are fundamental differences between
a router and a
layer 3 switch.
+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:
-A layer 3 switch is not a multi-port router, however
, a Cisco
layer 3 switch like a Cisco Catalyst 3550 series switch
and a Cisco Catalyst 3750 switch can be configured
as a multi-port
router, a pure
layer 3 switch, or a hybrid router/layer 3 switch
.
+; __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.
+; %%% __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.
+; %%% __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)
.
-Firstly, a router only makes packet switching (forwarding) decisions at
layer 3, whereas
a layer 3 switch makes a packet switching (forwarding) decisions at both layer 2 and layer 3.
-
-
-A layer 3 switch supports VTP (vLAN Trunking Protocol), a router doesn't, even though it does support 802.1q and ISL vLAN Trunks, that is only done
as an end point
, (just like a NIC that also supports 802.1q or ISL).
-
-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). Interfaces on a
router are seen as router interfaces, apart from creating bridge groups
.
-
-
-in
Cisco Catalst
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 it's
own switching processor which are the
dCEF[1
] modules in the Cisco world.
(aCEF[2]
modules uses
the switching processor on the Supervisor
card).
-
-----
-[1] dCEF = distributed Cisco Express Forwarding
-[2] aCEF = accelerated Cisco Express Forwarding
+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).
