Re: Fragment question again ..

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