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