Just to clarify.. MPLS labels (stack/single label) will be inserted between L2 and L3. so, in case of IP packets encapsulated in MPLS, the packet should look like,
PHY-- L2 header(source/ destination MAC etc)----- MPLS label stack [label1:label2:label3]------------ L3 header (Source/Des IP) in the above format, only Lable3 will have Bos set to 1, indicating it is on bottom of the stack and all other labels have Bos = 0. (we can have any number of labels and the point is the last label-bottom- will have Bos =1) Am i clarified you? Thx, Venkat On Thu, Apr 8, 2010 at 6:39 PM, Cristian Nedelcu < [email protected]> wrote: > ok ..Label 20 will be on Top(on top of ip header). but why with BoS set to > 0? I now that BoS identify identifying label next to the IP header. > > > On Thu, Apr 8, 2010 at 4:01 PM, venkat <[email protected]> wrote: > >> Hi, >> >> 1) when the packet come with label 23, is swapped with label 20..then >> label 16 is pushed onto 20 but in LFIB only the top label is showed? >> >> >>> According to the attachment, the label 23 will be swapped with 16 and >> a label 20 (top label, Bos=0) will be pushed as a top label. >> >> 2) Tag Stack{20 16} .. label 20 will be on top of IP header,BoS set to 1? >> so here the frame will look like this : [L3][20,16][L2] ? >> >> >>>> Label 20 will be on Top. But with Bos= 0. If Bottom of stack (BoS) is >> set to 1, then that label is at bottom of the stack. Middle/top label with >> have BoS = 0. >> Frame looks like as you said [MPLS payload/L3] [20 16] [L2]. >> >> Thx, >> Venkat >> http://ippoint.wordpress.com/ >> >> On Thu, Apr 8, 2010 at 5:22 PM, Marko Milivojevic <[email protected]>wrote: >> >>> On Thu, Apr 8, 2010 at 11:21, Cristian Nedelcu >>> <[email protected]> wrote: >>> > i don't understand verry well this part.. so..check out the output from >>> > attachment >>> > my questions are : >>> > 1) when the packet come with label 23, is swapped with label 20..then >>> label >>> > 16 is pushed onto 20 but in LFIB only the top label is showed? >>> > 2) Tag Stack{20 16} .. label 20 will be on top of IP header,BoS set to >>> 1? >>> > so here the frame will look like this : [L3][20,16][L2] ? >>> >>> In order to fully answer this, some more context would be nice. Just >>> by looking at this output, I would say this is MPLE TE environment >>> (I'd venture a guess that it could even be FRR recovery in action), >>> with 16 being the tunnel label and 20 the actual label applied for the >>> tail-end. The prefix is switched using tunnel label, but tunnel is not >>> a physical interface. When the packet gets to the wire, it needs to >>> have a "real" label, hence additional label on the stack. >>> >>> -- >>> Marko Milivojevic - CCIE #18427 >>> Senior Technical Instructor - IPexpert >>> >>> YES! We include 400 hours of REAL rack >>> time with our Blended Learning Solution! >>> >>> Mailto: [email protected] >>> Telephone: +1.810.326.1444 >>> Fax: +1.810.454.0130 >>> Web: http://www.ipexpert.com/ >>> _______________________________________________ >>> For more information regarding industry leading CCIE Lab training, please >>> visit www.ipexpert.com >>> >> >> >
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