Re: Fragment question again ..

So you mean to say that whenever furthur fragmentation takes place ..
MF is set to 1 in all sub-fragments ?

On Mon, Sep 27, 2010 at 2:56 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
> 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
>>>
>>>
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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 - 15:17:52 ART