djek2000
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Difference between router and layer 3 switch
Hi there,
I've been reading about layer 3 switching and understand that it is basically routing, done by hardware i.s.o. software like in the more traditional routers.
I've been reading about how all the router functionality that a layer 3 switch can handle but I hardly can't find any information about what layer 3 switches cannot do if compared to routers.
The only thing I found is that routers are still needed to connect to other types of networks.
Anyone know more about this? or can tell me where I can find more information on these differences between routers and layer 3 switches?
Thanx.
I've been reading about layer 3 switching and understand that it is basically routing, done by hardware i.s.o. software like in the more traditional routers.
I've been reading about how all the router functionality that a layer 3 switch can handle but I hardly can't find any information about what layer 3 switches cannot do if compared to routers.
The only thing I found is that routers are still needed to connect to other types of networks.
Anyone know more about this? or can tell me where I can find more information on these differences between routers and layer 3 switches?
Thanx.
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The main difference is that a Layer 3 switch only routes the first packet in a flow. Once the route is determined, the packet forwarding is off-loaded to the switching engine. This leaves the router to perform other tasks and dramitically inreases the perfomance since most of the packets are effectively switched. As lrmoore pointed out, Layer 3 switches tend to leave out some of the more robust routing features that would be more suited to a dedicated routing device, although you can get those features on some L3 switches if you have the $$$$.
ASKER
what you're reverring to is 'route once, switch many'..... i've read about this somewhere.
so how does a the layer 3 switch know if a packet is the first in a flow? Is this taken from a the IP header?
so how does a the layer 3 switch know if a packet is the first in a flow? Is this taken from a the IP header?
The switch maintains a MAC-address table and arp cache. Once the first packet destination is identified, it has to look up the MAC address and identify the port, the just lets the flow out that port...
G'day, djek2000
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