Requested revision
Standard: | 802.1AB-2009 | Clause: | 6.6.1, 9.2.7.7.2, 10.5.2 |
Clause title: | LLDPDU and TLV error handling |
Rationale for revision
The text for General validation rules for TLVs (9.2.7.7.2) isn't
consistent with the text for LLDPDU and TLV error handling (6.6.1)
The latter implies that if an LLDPDU contains a detectable error
then the entire PDU and its contents are discarded, but 9.2.7.7.2 c)
states that there are cases (and explicitly cites E.3.3) where it is
acceptable to discard a single errored TLV and process the rest of
the PDU. There have been questions from implementers regarding what
is intended.
Additionally, there are some inconsistent statements about how to
handle the incrementing of statsFramesInErrorsTotal. The description
of statsFramesInErrorsTotal in 10.5.2 is: A count of all LLDPUPDUs
received at the port with one or more detectable errors 9.2.6.3).
Note: The standard is missing the opening parenthesis on the
reference. 9.2.6.3 agrees with the definition in 10.5.2. Therefore
it should only increment once per frame. However, the TLV validation
rules in 9.2.7.7.2 increment statsFramesInErrorsTotal whenever they
increment statsTLVsDiscardedTotal. They could increment it multiple
times per frame.
Proposed text
Change 6.6.1 to say something like the following:
The LLDPDU is checked to ensure that it contains the correct
sequence of mandatory TLVs and then each optional TLV is validated
in succession. LLDPDUs that contain detectable errors in the
mandatory TLVs are discarded. Optional TLVs that contain detectable
errors are discarded (see 9.2.7.7.2 c)). TLVs that are not
recognized, but that also contain no basic format errors, are
assumed to be valid and are stored for possible later retrieval
by network management (see 9.2.7.7.1 and 9.2.7.4).
Change 9.2.7.7.2
Remove mention of statsFramesInErrorsTotal from a) through e) and add
an additional rule at the end saying that statsFramesInErrorsTotal
is incremented at the end of processing if the LLDPDU or any of the
TLVs in it were discarded.
Change 10.5.2
Add the missing opening parenthesis to item b) 3).
Impact on existing networks
Potentially, fewer LLDPDUs will be discarded in their entirety
and only incorrect TLVs will be missing. The MIB error statistics
may show fewer statsFramesInErrorsTotal. These differences are
very unlikely as incorrectly formatted TLVs are rare, so the
overall impact is very minimal.
Originator
Name: | Paul Congdon, Pat Thaler | Email: | paul.congdon@hp.com, pthaler@broadcom.com |
Affiliation: | Hewlett-Packard, Broadcom | ||
Submitted: | 2011-11-07 |