Re: Fragment question again ..

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
>
>
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Received on Mon Sep 27 2010 - 11:18:00 ART