The MPLS WG Archive

[David Charlap <David.Charlap@marconi.com>]

Adrian Farrel wrote:
> 
> According to RFC3209 what is the correct behavior of an upstream LSR when it receives a
> PathErr?Should it:
> - forward the message but retain Path and Resv state

Yes

> - forward the message and retain Path state but discard Resv state
> - forward the message and retain no state
> - something else.
> References would help.

Unless a specific PathErr/ResvError's specification says otherwise, you
should forward error messages to the appropriate ingress/egress node(s).
  The edge nodes should do all the real work.

See RFC 2209 - message processing rule for RSVP.  Section 2.

PathError:

	...

	PERR MESSAGE ARRIVES

	o Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
	  matches the corresponding objects in the message.  If no
	  matching PSB is found, drop the PERR and return.

	o If the previous hop address in the PSB is the local API,
	  make an error upcall to the application:
	    ...
	  Otherwise, send a copy of the PERR message to the PHOP IP
	  address.

	o Drop the PERR message and return

ResvError:

	...

	RERR MESSAGE ARRIVES

	A RERR message arrives through the (real) incoming interface
	In_If.

	o If there is no path state for SESSION, drop the RERR
	  message and return.

	o If the Error Code = 01 (Admission COntrol failure), do
	  special processing as follows:
	    ...
	  (description of blockade-state algorithm snipped)

	o Execute the following for each RSB for this session whose
	  OI differs from In_If and whose Filter_spec_list has at
	  least one filter spec in common with the FILTER_SPEC* in
	  the RERR message.  For WF style, empty FILTER_SPEC*
	  structures are assumed to match.

	  1. If Error_Code = 01 ...
	     (special handling for blockade procedure snipped)

	  2. If NHOP in the RSB is the local API, then:

	     - If the FLOWSPEC in the RERR message is strictly
	       greater than the RSB Flowspec, then turn on the
	       NotGuilty flag in the ERROR_SPEC.

	     - Deliver an error upcall to application:
	         ...
	       and continue with the next RSB

	  3. If the style has wildcard sender selection...
	     (snip - WF is not applicable to MPLS)

	  4. Create a new RERR message containing the error flow
	     descriptor and send to the NHOP address specified by
	     the RSB.  Include SC.Out if the style has wildcard
	     sender selection.

	  5. Continue with the next RSB

	o Drop the RERR message and return.

-- David