First, this HAS been covered... a bit in the thread
here, but it's quite old and I'm not sure how y'all feel about thread necromancy here, so I'm starting a new one.
This stems from a particular paragraph (and assosciated figure) in the ISCW Exam Certification Guide (Cisco Press) that simply defies my interpretation and understanding of the whole point of MPLS.
as follows:
The LSP is essentially a tunnel between source and destination for a particular FEC. Zooming out, it would look more like a tunnel with many forks in the road, because it is feasible for two FECs to share a label at one point, then diverge at another.
I've also attached the figure.
My question is simply: HOW!?!? if the whole concept and purpose behind MPLS is that any non edge LSR will forward based ONLY on the label of an incomming packet, then if at any point two FECs use the same inbound label, wouldn't they, from that point on, be effectively the same FEC and have no opportunity to diverge until the labels were popped?
So, are these statements simply wrong? or am I completely loosing my mind here?
Any insight would be appreciated, before my head explodes, thanks
actually, it has occured to me that there's an easy way to visualize what I'm talking about:
(NOTE: periods are spaces, it won't let me leave whitespace, so I have to use periods...)
Based upon MY understanding, you could have this:
FECA-->--->--->\
........................>FECC>--->--->--->Edge LSR
FECB-->--->--->/
but NEVER this:
FECA-->-->-->\
................... /-->FECA-->
......................>FECC>-->-->
FECB-->-->-->/
...................\-->FECB-->
which is pretty much the opposite of what the book is saying, as far as I can tell.
