Re: Fragment question again ..

Nope, "last fragment" is the fragment that has the last byte of the
initial packet. There is one and only one of those.

The other fragments have MF=1, even those that are "last sub fragments"
if this means anything.

-Carlos

GAURAV MADAN @ 27/9/2010 7:09 -0300 dixit:
> That's what I meant Carlos .. Sorry if I am not understanding you .
>
> If what you are saying is true ; the last router will get more than
> one Fragment with MF = 0
>
> Again stating example
>
> Frag 1 : 1500 byte
> Frag 2 : 1500 byte
> Frag 3 : 1500 byte
> Frag 4 : 500 byte
>
> Frag 1 ,2 , 4 goes on PATH # 1
> Frag 3 goes on PATH # 2
>
> At beginning MF =1 in frag 1 , frag 2 , frag 3 .. Frag 4 has MF = 0 (
> no more fragments )
>
> Now for fragment that goes on path # 2 is furthur fragmented .
>
> 3.1 : 500 bytes
> 3.2 : 500 bytes
> 3.3 : 500 bytes
>
> 3.1 and 3.2 has MF =1 and 3.3 has MF = 0
>
> Therefore at receiving router ; Frag 4 as well as frag 3.3 has MF = 0
> This leads to problem
>
> Thnx
> Gaurav !
>
> On Mon, Sep 27, 2010 at 3:34 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
>> 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
>>>>>>>
>>>>>>> _______________________________________________________________________
>>>>>>> Subscription information may be found at:
>>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> --
>>>>>> 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
>>

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