need help about subinterface and BW issue

[Dr.X]

hi,

i would like to ask a question

what is the relation between the bandwidth for a subinterface when i perform a subinterface, i mean point to point , and multipoint.

as an example , if i have a serial interface s0/0 , we know that the bw = 1.5 mbps for that physical interface.

now when i make 5 subinterface , 2 multipoint and 3 point to point .

how does the bw is redistributed , imean "1.5 mbps " to the other interfaces after performing subinterfaces ???

another question,can we use the physical interface if we perfomed any subinterface on thaT PHYSICAL interface ???

regards

[Joseph W. Doherty]

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The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

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Posting

If you're asking what (serial) subinterfaces will default their logical bandwidth, I don't recall.  It might be the same as the parent interface.

In actual usage, each subinterface, assuming no other subinterfaces are passing traffic, should be able to use the full physical interface bandwidth.

Can you use the parent interface if subinterfaces are defined/used?  Believe you usually can.

[Dr.X]

you mean that all logicals interfaces assume that it is unique and have the access to full bw ???

another question , can i say that the 1.5 mpbs "full bw" is being shared by logical interfaces when many logical interfaces works in the same time ???

regards

[lucentmoon]

Any one subinterface can use the full 1.5 bandwidth,  But multiple subinterfaces cannot exceed a total of1.5mbps traffic on the physical line.  So if you have 2 subinterfaces both set to use 1.5mbps you will probably run into congestion, as the physical interface can only handle 1.5mbps TOTAL.  Therefor it is best to set the bandwidth of your subinterfaces to total 1.5mbps.  for example 2 subinterfaces @ 768kbps, or 3 subinterfaces at 512, etc.

[Dr.X]

it is recognized that the subinterfaces cant access more that the physicl bw and this is a logical idea

but you may gave me new info which is , the bw between subinterfaces is not shared and congestion may occur, and to solve this issue , i have to se the bw manually.

is there any misunderstanding in what i ve typed .???

thanks alot for your preciuos information & help

[Joseph W. Doherty · Accepted solution]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

Subinterfaces do share the physical interface's available bandwidth.

It doesn't matter what subinterface interface bandwidth is set to for normal subinterface sharing, as this configuration statement is only a logical setting.

It does matter, though, if you shape or police subinterfaces.  It can matter if your dynamic routing protocol selects subinterfaces based on logical bandwidths.