Determine bw for VLAN

larkspur

I am using a NetFlow collector. I have set up IP groups to determine how much bandwidth vlan 2 is using.

My question is to accurately determine how much bw a vlan is using do I need to total up the speed that each interface particapting in that vlan is set to?

example:
3 100 meg interfaces in vlan 2 = 300000000 bps

vlan 2 bandwidth capaicty is 300000000 bps.

Would this be correct?

rossonieri#1

hi larkspur,

if you are talking about theoritically full rate data transfer - then yes its about 3x100Meg in VLAN2.
but we use a multiplexing/compression ratio - not all your 3 interfaces talk in the sametime - using the same protocol (different protocol utilize different speed etc), cabling distance, electricity and so on.

cheers.

Paul Boz

It depends more on the bandwidth of your trunk links than anything else. If you have 3 100mb vlan ports that are trunked with a 100mb port and have to send packets across that trunk link your capacity drops down to 100mb. You can't shove 10 pounds of sausage into a 3 pound casing, after all.

larkspur

this is my bad for not providing better info.

core swicth (6509)

trunk links to access\distribution swicthes (3750g's)

trunk link speed is 1 gig.

So there are 3 1 gig trunk links to the 3750's which particpate in vlan 2.

so the total bandwidth for vlan 2 would be 3 gig or 3000000000 bps and not the combined port speed of all interfaces ( server etc..) particapting in vlan2 ?

rossonieri#1

larkspur wrote:

this is my bad for not providing better info.

core swicth (6509)

trunk links to access\distribution swicthes (3750g's)

trunk link speed is 1 gig.

So there are 3 1 gig trunk links to the 3750's which particpate in vlan 2.

so the total bandwidth for vlan 2 would be 3 gig or 3000000000 bps and not the combined port speed of all interfaces ( server etc..) particapting in vlan2 ?

yes - i wished i know about trunk lines more better.

the global def about trunk line is a line (either single nor aggregrate) which carries multiple line.
the main line - is that the carried line BW will never exceed the trunks.

does a cat6500 single 1 gig port will carry a cat2900 24x100meg on their trunk?
the answer is very clear.
cheers.

HTH.