MPLS TE Bandwidth and Priority

Question

Hi everybody
Hopefully, everyone is doing great.  I stumbled upon the following link on MPLS TE bandwidth and priority:
http://blog.ipexpert.com/2009/05/27/mpls-te-bandwidth-and-priority/
it was a very good read.  But I am left with one question. How does R2 decide which tunnel to drop? In the example, R2 drops tunnel 1, but how does R2 decide which one to drop?
Thanks and have a great sunday

Answer 1

Hi Thanveer
I hope you are doing fine.  Here is what i found  in a book ( traffic engineering with MPLS by Eric, Ajay, great book, still reading it)
There are two priorities:
1) set up priority
2) hold prioritity
Based on the book the code works this way
Imagine we have two tunnels already established and are passing through R3
t1, set up priority 6 hold priority 5
t2 set up priority 6 hold priority 4
Let say R3 just receives a RSVP path  request for  a new tunnel, lets call it tunnel 3 with set up priority 4 hold priority 6. This tunnel requires a bandwidth which R3 can not accommodate without dropping one of the established tunnels.
Router will take t3's set up priority ( 4) and compares it against the current  established tunnel's hold priorities where lower the number means higher the priority. In our example, set up priority of tunnel 3  is 4 and R3  compares it against both hold priorities of established tunnels. R3 then concludes it has to drop t1 to accommodate t3 ( set up priority of tunnel3 is higher than the hold priority of tunnel1)
++++++++++++++++++++++++++++++++++++++++++++++++++++++
what is not cleared is how will router 3 behave if all the established tunnels have same hold priority i.e 4 and a request for a new tunnel i.e t3 comes with the set up priority of 4?
Not sure if R3 just randomly picks any established tunnel and drops it or there is some move involved process that R3 goes through to decide which tunnel gets dropped.
Lets hope somebody way smarter than me might chime in :)
Have a great weekend