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.C.Rosen,
MPLS WG
E.g., PWE3 defines FECs for
binding labels to PWs
11/9/04
1
HA FEC vs. AP FEC
• What’s the difference between:
– HA FEC and
– AP FEC with /32 address?
• Some claimed: egress LSR must
distinguish, from top label:
1.whether packet is addressed to it,
or
2.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.
E.C.Rosen,
MPLS WG
11/9/04
2
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
E.C.Rosen,
MPLS WG
11/9/04
3
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?
E.C.Rosen,
MPLS WG
11/9/04
4
MPLS Forum’s 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
E.C.Rosen,
MPLS WG
11/9/04
5
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
E.C.Rosen,
MPLS WG
11/9/04
6
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
E.C.Rosen,
MPLS WG
11/9/04
7