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LSP-Trace over MPLS tunnelsdraft-nitinb-lsp-ping-over-mpls-tunnel-01

Nitin Bahadur Juniper NetworksKireeti Kompella Juniper NetworksGeorge Swallow Cisco Systems

IETF 70, MPLS WG, Vancouver

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Tracing a hierarchical LSP

A B C ED

LDP

LDPLDP

RSVPRSVP

Options available at node B:

• Do not allow tracing inside RSVP LSP

• Allow tracing inside RSVP LSP

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Problem scenario (1): Tracing a hierarchical LSP

A B C ED

LDP

LDPLDP

RSVPRSVP

• Node B’s “effective” next-hop for LDP LSP is node D

• However the “real” next-hop is node C

• Node A sends echo request with LDP FEC to node C

• Node C knows nothing about LDP FEC, so cannot perform FEC validation.

• Node A cannot tell why it is getting a response from node C

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Solution

A B C ED

LDP

LDPLDP

RSVPRSVP

• Intermediate node (router B) provides a PUSH FEC stack tlv containing <RSVP> in DSMAP of echo response

• Ingress (router A) pushes RSVP onto it’s FEC stack in echo request when sending next echo request (to router C)

• When router D receives echo request with FEC stack containing <RSVP, LDP>, it sends Egress-Ok for RSVP FEC

• Implicitly conveys that RSVP LSP is over -- pop it

• Ingress (router A) now pops an entry from (local) FEC stack and resends echo request to router D with LDP FEC

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Problem Scenario (II): Tracing a stitched LSP

A B C ED

RSVPLDP eBGPLDP

F

RSVP

No current mechanism to perform end-to-end trace of stitched LSPs.

Current trace mechanisms will only trace till router C.

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Solution

• Intermediate node (router C) provides a POP FEC stack sub-tlv (LDP) and PUSH FEC stack sub-tlv (eBGP) in DSMAP of echo response.

• Ingress (router A) performs the corresponding stitch operation and sends eBGP FEC in next echo request (to router D)

• Router D provides a POP FEC stack tlv (eBGP) and PUSH FEC stack sub-tlv (RSVP) in DSMAP of echo response.

• Ingress (router A) performs the corresponding stitch operation and sends RSVP FEC in next echo request (to router E)

• Router F responds with EGRESS_OK for the end-to-end LSP.

A B C ED

RSVPLDP eBGPLDP

F

RSVP

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Solution concept

• Intermediate routers provide ingress information regarding:– start of a new tunnel– end of a tunnel– tunnel stitch.

• FEC details can be hidden by sending a NIL FEC, instead of actual FEC being pushed.

• Analogous to push/pop operations in the data-plane.• Main logic at ingress application to correctly traverse the

tunnels

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TLV changes proposed …

• Builds on RFC 4379 (LSP-Ping)• Downstream Mapping TLV deprecated

– Not extensible: can’t have sub-TLVs (blame Kireeti!)– Not easy to associate new information in echo response

• Downstream detailed mapping TLV introduced– Similar to previous one– Contains sub-TLVs to represent all variable length things– New sub-TLVs can be added in future to associate things with

DSMAP.

• Procedures outlined to deal with old and new TLV formats.

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Downstream Detailed Mapping TLV

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MTU | Address Type | DS Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream IP Address (4 or 16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream Interface Address (4 or 16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-tlv length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + List of Sub TLVs + + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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DDMAP Sub-TLVsMultipath Sub-TLV 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Multipath Type| Multipath Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | (Multipath Information) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Label-stack Sub-TLV 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream Label | Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream Label | Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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DDMAP Sub-TLVs (contd.)Stack change sub-TLV

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Operation Type| Address type| FEC-tlv length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote Peer Address (0, 4 or 16 octets | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . FEC TLV . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Operation Type # Operation----------------------- --------- 1 Push 2 Pop

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Next Steps

• WG feedback on problem/solution

• Adopt as WG doc ?