The MPLS-OPS Archive

["M. ELK" <elkou141061@hotmail.com>]

Hi

Consider the following :

PE1-----Netw cloud1 --P1-------Netw Cloud2---P2---Netw Cloud3--PE2 .

TE1 LSP between PE1 to  P1 , TE2 LSP between P1 to P2 , TE3 LSP between P2 
to PE2 .

(Targetd LDP between PE1& P1 , P1 & P2 , and P2 and PE2 ) .

Say when we trace the LDP LSP of PE2 from PE1 .

is the trace output = P1,P2,PE2 ,let us call it  "Plain trace"

or

The trace outpt is all transit nodes actually traversed= .
PE1,Nodes In ntew cloud1 , P1 ,Nodes in netw cloud2 ,P2,Nodes in netw 
cloud3,PE2 .
let us call it "Recursive Trace" .

My question :

1- when the "LSP trace"  wording is used , is it mean "Plain trace" or 
"Recursive trace" ??
2- My guess that the operator shoud be given the option to request either 
the "Plain Trace"
   or the "Recursive Trace" .
   For the above setup : say P1 advertise label L1 for PE2 FEC to PE1 .
   "Plain Trace"= PE1 will increment the TTL value for L1 and not the top 
most labels (labels above
    - ie: nearest the top - L1 in the stack  ) . The top most labels (above 
L1) will have TTL=255 .
      we assume that all TE LSP are pipe or short pipe model .

    "Recursive Trace" =
PE1 will increment the top most label while any label beneath this top most 
loabel will have TTL=1 .
By this PE1 , will trace all nodes in Netw_Cloud1 and P1 .
say this occur at TTL=10 ,and the reply will be from P1 .
at TTL=11 , the reply will also come from P1 , this indicate to PE1 that it 
is now to start to
increment the TTL of the label beneath the top most label . ie: the next 
attempt the top
most label will have TTL=11 , and the label beneath (L1 in our case) will 
have TTL=2 .
But since TE LSP's are pipe or short pipe the output of the trace will be :
Nodes in Netw_cloud1,P1,P2,PE2 .
we will not be able to find out the nodes in netw_cloud2 and nodes in 
netw_cloud3 ??

is this a correct conclusion ?? .
How we could trace nodes in netw_cloud2 and netw_cloud3 ??

3- My guess that "Recursive trace" is only possible if the TE LSP's are 
Uniform model , but in this
   case "Plain trace" is not possible .
   is the above a true statement ???.

Brgds

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