Re: Fragment question again ..

Gaurav,
Please don't change my words. I said it will not set MF=0, i.e., it will
set MF=1 in all fragments because non of the new fragments is a last
fragment, and it knows that.
Identification should be the same as the incoming fragment too.

You can test this if you feel different.
-Carlos

GAURAV MADAN @ 27/09/2010 2:48 -0300 dixit:
> Hi Carlos
>
> Any router which is fragmenting a larger pkt in small is supposed to
> write 3 things :
>
> 1) Identification
> 2) Flag bits ( 3 bits including DF , MF )
> 3) Offset .
>
> Hence when you say that router which is fragmenting the already
> fragmented packet will not write Flag bits is NOT CORRECT .
> Thats what i feel .
>
> Thnx
> Happy !
>
> On Mon, Sep 27, 2010 at 12:59 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
>> Happy,
>> MF = 0 means this is last fragment for initial packet. The second
>> fragmentation of a non last fragment will not set MF = 0 in any
>> fragment. Offsets are also from the begining of the packet always, as
>> you describe.
>>
>> Also, there is no hierarchy of fragments, just fragments.
>>
>> -Carlos
>>
>> Happy Singh @ 26/09/2010 6:29 -0300 dixit:
>>> R1 -------------- R2 -------------- R3
>>> | |
>>> | |
>>> | |
>>> R4---R5----R6------R8-----------
>>>
>>>
>>> Hi All
>>>
>>> Last week I discussed a few points abt fragmntation in IP networks .Thnx for
>>> all help . Here is a interesting scenario which i wanted to clearify
>>>
>>> Let 5000 byte pkt is rx on R1 . R1 makes 4 fragments : 1500 , 1500 , 1500 ,
>>> 500
>>>
>>> Let is sends Frag 1 ( offset 0 ) , Frag 3 ( offset 3001 ) , fragment 4 (
>>> offset 4501 ) to link1
>>> Let it sends Frag 2 ( offset 1501) to link 2
>>>
>>> Last fragment on link 1 will have MF = 0 ; others will have MF = 1 ( MF =
>>> more fragments )
>>>
>>> Now the pkt that goes via R4--R5--R6--R8 is required to be further
>>> fragmented ( due to even smaller MTU )
>>> Let it is broken as frag 1 ( offset 1501) ; frag 2 ( offset 2001) ; frag 3 (
>>> offset 2501 ) : 4 sub-fragments of 500 bytes each .
>>> Now these will have MF = 1 and fragment with offset 2501 will have MF = 0
>>>
>>>
>>> Question is : AT assembling router (R3) ; we are getting 2 fragments with
>>> MF = 0 . This will cause problem because if fragment 4 ( offset 4501 ) with
>>> MF = 0 is recieved before frag # ( offset 2501 ) then it might assume that
>>> since MF = 0 ; I am not expecting any other fragments .
>>>
>>> Please tell me how is this taken care of in routers ?
>>> I hope I have made my question clear ,
>>>
>>> Thnx
>>> Happy !
>>>
>>>
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>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
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>>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net