Re: Fragment question again ..

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
>>>>>>
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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
Received on Mon Sep 27 2010 - 15:39:06 ART