LSP-Trace over MPLS tunnels

1
LSP-Trace over MPLS tunnels

• draft-nitinb-lsp-ping-over-mpls-tunnel-00
• Nitin Bahadur Juniper Networks
• Kireeti Kompella Juniper Networks
• IETF 69, MPLS WG, Chicago

2
Tracing a Tunneled LSP

• Do not allow tracing inside RSVP LSP
• Allow tracing inside RSVP LSP

3
Problem scenario
Allow tracing inside RSVP LSP

• Node Bs next-hop for LDP LSP is node C
• Node A sends echo request with LDP FEC to node C
• Node C knows nothing about LDP FEC, returns
  error
• Node A reports trace error

4
Problem Statement

• For hierarchical LSPs or LSPs tunneled over other
  LSPs, we should be able to trace the entire
  end-to-end path.
• Intermediate outer-LSP nodes should allow inner
  LSP trace to go through
• Intermediate outer-LSP nodes not required to
  provide detailed information about outer LSP

5
Solution

• Intermediate node (router B) provides a FEC stack
  of ltRSVP, LDPgt in echo response
• Ingress (router A) uses that FEC stack in echo
  request when sending next echo request (to router
  C)
• When router D receives echo request with FEC
  stack containing ltRSVP, LDPgt, it sends Egress-Ok
  for RSVP FEC
• Ingress (router A) now pops an entry from (local)
  FEC stack and resends echo request to router D
  with LDP FEC

6
Solution (contd.)

• Intermediate routers provide ingress information
  regarding start of a new tunnel.
• FEC details can be hidden by sending a NIL FEC in
  response (ltNIL, LDPgt instead of ltRSVP, LDPgt)
• Main logic at ingress application to correctly
  traverse the tunnels

7
TLV changes proposed by draft

• Builds on RFC 4379 (LSP-Ping)
• Intermediate routers that are ingress of a new
  tunnel/LSP-segment modify the echo response as
  follows
• Add a bit in DSMAP to indicate more data is
  associated with DSMAP
• A new Downstream FEC stack TLV is added
• Contains information to associate with particular
  DSMAP
• Contains FEC stack (similar to that in echo
  request) for tracing downstream

8
Next Steps

• WG feedback on problem/solution
• Adopt as WG doc ?