switch speed question

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1

Hi

Can you share your experience what is fastest Gig switch?

I see there is CEF feature in cisco.

ls it big different when i enable it in switch vs other switch?

ls there any problem?

Thank you

2

Can you elaborate a bit on your question? The fastest "Gig switches" can do 1GB full speed on the port. There are many that can do that.
Do you have a particular density you need to do full speed with? Any particular features? Are you looking at any particular models now, in others words have you
even begun to explore this before posting here? Are you looking at Layer 3 switching, I assume you are since you are asking about CEF. Every manufacturer has a way
of switching the packets, Cisco uses CEF, and yes if you enable CEF its a big difference vs. a netgear gig switch from best buy, but I think you are wanting more of an answer than that
and you just need to give us some more info.

Brian

3

Hi,

It depends on how heavily loaded your switch is expected to be, for instance
two machines using the switch will be able to get a full 1Gbps, however
depending on the backplane (switching fabric), it limits how many ports will
receive full 1Gbps when the switch is congested, e.g. a 2 gig backplane
against a 24 gig.

Regards,

Bruce

4

Note that the traffic to a switch is bi-directional (full duplex) - so
a 24 port gigabit switch can max out its 32 Gig backplane, if all 24
ports have a gig coming in and going out (24 X 2 is 48, more than the
32 gig backplane).

This isn't immediately apparent - the other day someone at my work
asked the exact question "Why's the 32 gig backplane > the 24 ports on
the switch?"

5

That isn't always true. Some switches are already speced as full. It's best to read the product docs or speak with a rep to be sure.

tv

6

Arista claims to have the fastest 1/10 Gig 24 and 48 port 1RU switch,
with a backplane capacity guaranteeing 10 Gig full duplex line rate per
port.

Cisco's CEF is local only and functions to download the arp cache and
routing table into ASICs for hardware switching; but look at Cisco's
NSF/SSO for cases where adjacent devices are all defined in the same
packet forwarding state machine.

7

Eric Gearhart wrote:

....

Note that the traffic to a switch is bi-directional (full duplex) - so
a 24 port gigabit switch can max out its 32 Gig backplane, if all 24
ports have a gig coming in and going out (24 X 2 is 48, more than the
32 gig backplane).

....
  

I think your math is faulty. While there may be 24G going in and 24G
going out, there is only 24G crossing the backplane. You can't count a
bit twice (once on in and once on out). Its the same bit.

8

Once upon a time, Roy <r.engehausen@gmail.com> said:

I think your math is faulty. While there may be 24G going in and 24G
going out, there is only 24G crossing the backplane. You can't count a
bit twice (once on in and once on out). Its the same bit.

Not every bit in results in just one bit out. Broadcast, multicast,
flooding for unknown MACs (or switching failures), ...