Similarities between a router and a layer 3 switch.
In essence they both
perform packet switching.
They both use
routing protocols and static routes to reach destinations which are not
directly connected
They both follow the
same process meaning:
They receive a
frame, strip off the layer 2 header
They perform a layer
3 lookup to find the outbound interface and next hop information
They encapsulate the
packet into a new layer 2 frame and transmit the packet.
Differences
between a router and a layer 3 switch.
A router connects
heterogeneous environments where as a layer 3 switch is usually used in
homogeneous environments.
A router uses multi
purpose hardware to switch packets, where as a layer 3 switch uses specialised
hardware (ASCI) to switch packets.
Because a router
uses multi purpose hardware it is
usually slower then a layer 3 switch.
Because a layer 3
switch uses specialised hardware it is generally common to see the switch
catering for only Ethernet environments,
where as a router because it primarily supports heterogeneous environments it
is common to see a router equip with different line cards e.g. frame relay,
isdn, atm, etc to support hetrogenious enviroment.
Adding new features
to a router can be done by just upgrading the software, which is not the case
in a layer 3 switching environment.
Differences between SVI and a routed port.
One of the primary
difference is a routed port do not have any layer 2 protocols enabled such as
STP and DTP
A routed port has a
direct co-relation between its interface status, meaning if a link is down ,
the routed port will be down also.
Where as an SVI
(meaning a vlan interface) is dependant on the ports associated with its vlan,
if there are 3 ports in a vlan, an SVI interface will still be up even if 2 out of the 3 ports are down.
A layer 3 switch can
do 3 additional things compared to a router.
It can switch within
vlan
It can switch
between vlans (inter vlan routing)
It can switch
between a vlan and a routed port (no switch port)
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