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MPLS Multicast Encapsulations

draft-rosen-mpls-multicast-encaps-00.txt

Toerless Eckert (eckert@cisco.com)

Eric Rosen (erosen@cisco.com)

Rahul Aggarwal (rahul@juniper.net)

Yakov Rekhter (yakov@juniper.net)

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Issue RFC 3032 defines two data link code points for

MPLS – For Unicast and Multicast. But..

• There is no need to reserve a code point to determine whether the top label is a MPLS multicast label

• The NHLFE will determine whether the top label is a MPLS multicast label

• The developments in MPLS multicast have shown that the definition of these code points with respect to MPLS multicast is not adequate

• Similar issue with RFC 4023 for MPLS in GRE

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Solution The semantics of the data link code points

as defined in RFC 3032 and RFC 4023 need to be redefined for MPLS multicast

• Align with developments in MPLS multicast

But before discussing details…

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Downstream Assigned vs Upstream Assigned Labels

Consider Ru (upstream LSR) and Rd (downstream LSR) as adjacent in a LSP for FEC F. The top label of the MPLS packet sent by Ru to Rd is L.

Downstream Assigned Label - Rd distributes the binding of FEC F to label L to Ru

Upstream Assigned Label – Ru distributes the binding of FEC F to label L to Rd

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MPLS Multicast and Upstream Assigned Labels

Ru is adjacent to <Rd1…Rdn> in a LSP and is connected to to <Rd1…Rdn> via a multi-access media or Tunnel.

Further Ru wishes to transmit a single copy of a MPLS Multicast packet belonging to the LSP to <Rd1…Rdn>

• The same top label must be received by <Rd1..Rdn> for this MPLS multicast packet

To accomplish this Ru assigns an upstream assigned label and distributes it to <Rd1…Rdn>

Upstream label assignment architecture in draft-raggarwa-mpls-upstream-label – Next presentation

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Back to Code Points Three different types of data links/tunnels

• P2P – downstream assigned labels only

• P2MP – All top labels must be downstream assigned or upstream assigned. Determined apriori

• MP2MP - Top labels may be downstream assigned or upstream assigned. Encapsulation must provide a code-point to make this distinction

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Ethernet Code Points and MPLS Multicast

Ethernet is an example of a MP2MP data link 0x8847 [unicast code point] is used for MPLS

multicast packets as long as the top label is downstream assigned.

• The MAC address is that of the intended recipient i.e. a unicast MAC

0x8848 [Former multicast code point] is used when the top label is upstream assigned

• The MAC address is a multicast MAC derived from the label – 01 – 00 - 5e - 8a - bc - de [abcde is the 20 bit label value]

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GRE Protocol Type and MPLS Multicast

Modifies RFC 4023

If the destination address is an IP multicast address and both downstream and upstream assigned MPLS labeled packets are carried on the same tunnel

• 0x8847 is used for downstream assigned lbls

• 0x8848 is used for upstream assigned lbls

If the destination address is an IP multicast address and only upstream assigned or only downstream assigned MPLS labeled packets are carried

• 0x8847 is always used

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IP Protocol Number IPv4 protocol number or IPv6 Next Header

Field is always set to 137

• The top label is always downstream assigned or always upstream assigned

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MPLS Upstream Label Assignment and Context Specific Label Space

draft-raggarwa-mpls-upstream-label-00.txt

Rahul Aggarwal (rahul@juniper.net)

Yakov Rekhter (yakov@juniper.net)

Eric Rosen (erosen@cisco.com)

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Scope RFC 3031 limits the MPLS architecture to

downstream assigned labels

This draft generalizes the notion of a per-interface label space to a “context-specific” label space

• Neighbor label space is introduced as an example of “context-specific” label space

This draft extends the MPLS architecture for upstream assigned labels

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Context-Specific Label Space RFC 3031 describes platform and interface based

label spaces This document describes the more general notion

of a “context-specific” label space• A LSR may maintain multiple context-specific

label spaces A context-specific label space may be used for

downstream-assigned or upstream-assigned labels

An interface-based label space is an example of a context-specific label space for downstream-assigned labels• Label space is determined by the interface

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Context-Specific Label Space and Upstream Assigned Labels

Upstream Assigned Labels are always looked up in a context-specific label space

The context is provided by the LSR that assigns and distributes the upstream assigned label binding, L for LSP1

The LSR that receives the upstream assigned label binding must be able to determine the context when it receives a MPLS packet with a top label ‘L’ on LSP1

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Context-Specific Label Space and Upstream Assigned Labels…

Tunnel Specific Label Space

• Determined by the tunnel on which the MPLS packet is received

• If the tunnel is a MPLS tunnel, PHP must be turned off

Neighbor Specific Label Space

• Determined by the neighbor from which the MPLS packet is received

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Upstream Assigned Labels Motivation was described earlier

A LSR may distribute upstream assigned labels for FEC F to its downstream LSRs and downstream assigned labels to its upstream LSRs

Two adjacent LSRs, Ru and Rd, on LSP LSP1 for FEC F must use either upstream label assignment or downstream label assignment for FEC F, for packets transmitted from Ru to Rd

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Assigning Upstream Assigned Labels

An upstream assigned label must be unambiguous in the context-specific label space in which the downstream LSR will look it up

For the upstream LSR, an upstream assigned label is an outgoing label and forms part of the NHLFE

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Distributing Upstream Assigned Labels

Must not be distributed unless its known that a downstream LSR supports them

• Requires protocol discovery extensions

• Assumption is that the downstream LSR can accept upstream assigned labels from the entire label range

Label distribution protocol considerations are based on RFC 3031

Distribution is similar to ordered LSP control or independent LSP control of downstream assigned labels

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Downstream LSR Requirements A downstream LSR must be able to

determine

• Whether a label is upstream assigned and

• The context-specific label space in which to lookup the packet

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Data Link Encapsulation Upstream assigned label is encapsulated

directly in a data link header by Ru

• Is the label upstream assigned ? – draft-rosen-mpls-mcast-encaps

• Rd maintains a separate neighbor label space for Ru

• What is the context ? Determined by the data link header. Eg. For ethernet, the source MAC address

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MPLS Tunnel Encapsulation Ru transmits the packet, the top label L of

which is upstream assigned, by encapsulating it in a MPLS tunnel

• Rd determines the context of this packet using the labels above L in the label stack

• One or more labels above L may also be upstream assigned

• Rd may maintain a separate label space for the tunnel or a single label space for Ru

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GRE Tunnel Encapsulation Ru transmits the packet, the top label L of

which is upstream assigned, by encapsulating it in a GRE tunnel

• Rd determines the context of this packet using the IP/GRE header – source/dest address

• Rd may maintain a separate label space for the tunnel or a single label space for Ru

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Conclusion Comments are welcome

We would like these drafts to be WG drafts