IP address in RRO & discovering downstream label for facility FRR

Consider the case :

R1--a---b--R2--c----d--R3--e----f--R4--g-----h--R5

where a,b,c,d,e,f,g anf h are the ip address of the interface .

the LSP ERO : b,d,f,h

RRO in the path msg :

sent by R1 : a

R2 : a,c

R3 : a,c,e

R4 : a,c,e,g

RRO in the Resv msg :

case 1:

sent by R5 : (h,L5)

R4 : (h,L5),(g,L4)

R3 : (h,L5),(g,L4),(e,L3)

R2 : (h,L5),(g,L4),(e,L3),(c,L2)

case 2 :

sent by R5 : (h,L5)

R4 : (h,L5),(f,L4)

R3 : (h,L5),(f,L4),(d,L3)

R2 : (h,L5),(f,L4),(d,L3),(b,L2)

Where L5 is the label assigned by R5 ,L4 by R4 ..etc .

In case 1 : the RRO in the path msg is identical to RRO in Resv msg ie:

symmetric recording but both do not match the ERO .

in Case 2 : The RRO in the path msg is not identical to the RRO in Resv

msg but RRO in RESV msg match exactly the ERO .

so is it case 1 or case 2 ??

For NNHOP fast reroute :

consider :

R1--a-----b--R2--c----d--R3--e---f--R4--g-----h--R5

| |

i m

| |

|----J--R6--K-----------|

a NNHOP Bypass Tunnel from R2 to R4 is manually created.

the egress (R4) is identified by LO4 (the R-ID

address of R4) . the ERO is : j,m

For labels : R4 advertise Null to R6

R6 advertise L6 to R2 .

Now when the interface "c" is down ,R2 protect

lsp (R1,R2,R3,R4,R5) by using the bypass tunnel

(R2,R6,R4) by swap label L4 (know from the RRO) and pushing the label L6 and forward the labeld packet on interface "i" .

What is not clear :

R2 knew from the RRO that L4 is allocated

by a node identified by "f" (case 1) or "g" (case 2) .

R2 knew that the bypass tunnel is terminated at node identified by "LO4" .

how R2 get to know that the node idendified by

"f" (or "g") is the same node identified by "LO4" so R2 could use L4 as the 2nd label in the stack ?

Could we have avoided this ambiguity if the RRO

record both :

1- The IP address of the outboud interface

AND

2-The IP Node Id .

Ie:

RRO in the Resv msg :

case 1:

sent by R5 : (h,L05,L5)

R4 : (h,LO5,L5),(g,LO4,L4)

R3 : (h,LO5,L5),(g,L04,L4),(e,LO3,L3)

R2 : (h,L05,L5),(g,LO4,L4),(e,LO3,L3),

(c,L02,L2)

case 2 :

sent by R5 : (h,L05,L5)

R4 : (h,LO5,L5),(f,LO4,L4)

R3 : (h,LO5,L5),(f,L04,L4),(d,LO3,L3)

R2 : (h,L05,L5),(f,LO4,L4),(d,LO3,L3),

(b,L02,L2)

So R2 knew that label L4 is allocated by a node

identified by L04 which is the same node terminating the bypass tunnel so R2 could use L4.

The above is also valid if the bypass tunnel egress is "m" instead of L04 as the RRO for this tunnel

will contain L04 as Node-ID associated with "m" so R2 could easily identify the association .

Brgds

The MPLS-OPS Archive

IP address in RRO & discovering downstream label for facility FRR