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RFC 3036 FECs

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RFC 3036 defines FECs used to bind labels to address prefixes in routing table. Two FECs defined: ... label used for management packets address to ... – PowerPoint PPT presentation

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Title: RFC 3036 FECs


1
RFC 3036 FECs
  • RFC 3036 defines FECs used to bind labels to
    address prefixes in routing table
  • Two FECs defined
  • Address Prefix FEC
  • Host Address FEC
  • Not all possible FECs
  • When labels are bound to other things, need other
    FECs
  • E.g., PWE3 defines FECs for binding labels to PWs

2
HA FEC vs. AP FEC
  • Whats the difference between
  • HA FEC and
  • AP FEC with /32 address?
  • Some claimed egress LSR must distinguish, from
    top label
  • whether packet is addressed to it, or
  • whether packet needs to be forwarded further
    (i.e., packet tunneled to egress LSR).
  • So need label which can be used only for 1, never
    for 2.

3
Functionality not Needed
  • LSR Egress specifies HA FEC for its own address
  • Corresponding label used for management packets
    address to that LSR
  • Is this needed?
  • Was always doubtful
  • Never been used
  • The DS needs to remove this functionality

4
Another Party Heard From
  • MPLS/FR Forum has proposal using HA FEC
  • Issues
  • Are they really using HA FEC as defined in RFC
    3036, or
  • Are they using only a subset of that
    functionality, so that the rest can be discarded,
    or
  • Are they extending LDP in a way which requires a
    new FEC?

5
MPLS Forums Proposal
  • CE sends to Ingress PE
  • Label Request with HA FEC and Traffic Parms TLV
  • Makes a resource reservation
  • Ingress PE responds with label
  • Same label may be assigned to multiple HA FECs,
    if they all have the same egress PE
  • Ingress PE uses label to find corresponding
    reservation
  • Ingress PE may base forwarding decision for
    labeled packet on IP address of packet

6
Observations on Forum Proposal
  • Violates RFC 3036/3.5.7.1
  • this use of HA FEC does not require a routing
    table entry for the address
  • Strange data plane semantics
  • PE may or may not look at IP address
  • Suggests that the LSP can only be one hop long
  • Downstream on Demand only
  • whereas RFC 3036 defines for DU ordered mode
  • Forwarding Equivalence Class is set of packets to
    which a particular resource reservation should be
    applied

7
Conclusions
  • New FEC has been implicitly defined
  • New FEC type must be defined
  • Resource reservation is part of the FEC
  • Advantages of using new FEC type
  • No issues of how HA FEC is handled or what it
    means in non-Forum situations (e.g., DU, no
    reservations)
  • Use of HA FEC in non-Forum situations would be
    error
  • Unused functionality discussed earlier can be
    eliminated from LDP
  • Forum can freely define label and FEC semantics
    without worry of conflict
  • No impact on non-Forum implementations
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