Re: Fragment question again ..

Yes, in all but the last fragment, that keeps generating the last
fragment no matter what.

GAURAV MADAN @ 27/09/2010 6:47 -0300 dixit:
> 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 !
>>>>>
>>>>>
>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>
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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
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>

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