The MPLS WG Archive

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

Bin Zhou wrote:
> 
> How does the Sender deal with the unrecognized subobject when it receive
> PathErr of "Bad Explicit Route"? Is it application specific? If it is, I can
> define the function for the unrecognized subobject in Sender.

The unrecognized object will be the first one.

We presume that the sender will understand what this object is, since 
the sender generated this object in the first place.

The sender has only two choices here.  It must either tear down the LSP 
and give up, ot it must re-signal the LSP with a different ERO object - 
one that does not contain the offending object.

> If the Sender request the route via R1 (only one subobject), the node on the
> left of R1 and R2 reply with a PathErr with a new route via R2. The error
> code is 24 (routing problem), the value is 1 (Bad Explicit Route), and new
> ERO (via ERO, only one subobject) is included. What's the behavior of
> Sender?

If the sender sends out a one-subobject ERO, then that subobject must 
identify the sender's immediate downstream neighbor.  That neighbor will 
recognize himself as the last node in the ERO and will proces the Path 
message as if there was no ERO.

I'm not sure I understand the scenario you're describing.

-- David


> 
> Regards,
> Bin
> 
> ----- Original Message -----
> From: "David Charlap" <David.Charlap@marconi.com>
> To: <mpls@UU.NET>
> Sent: Friday, August 09, 2002 10:10 AM
> Subject: Re: RSVP-TE PathErr: Bad Explicit Route Object
> 
> 
> 
>>bin wrote:
>>
>>>Question: What the exact ERO in PathErr is?
>>>
>>>In RFC3209,
>>>   "If there is no first subobject, the message is also in error and
>>>   the system SHOULD return a "Bad EXPLICIT_ROUTE object" error."
>>>
>>>   "A node which encounters an unrecognized subobject during its normal
>>>   ERO processing sends a PathErr with the error code "Routing Error"
>>
> and
> 
>>>   error value of "Bad Explicit Route Object" toward the sender.  The
>>>   EXPLICIT_ROUTE object is included, truncated (on the left) to the
>>>   offending subobject.  The presence of an unrecognized subobject which
>>>   is not encountered in a node's ERO processing SHOULD be ignored.  It
>>>   is passed forward along with the rest of the remaining ERO stack."
>>>
>>>I don't understand "truncated (on the left) to the offending subobject".
>>>Which subobject is the offending subject? What's the meaning of on the
>>>left?
>>
>>The offending subobject is the one that is unrecognized.
>>
>>"on the left" means everything prior to that object.
>>
>>
>>>In my understanding, explicit route object in Path State is not the
>>>original ERO sent by Sender, and the nodes along the route to this node
>>>are all removed from the ERO. The node should return only the
>>>unrecognized first subobject to the sender. Right?
>>
>>It should return the entire ERO, starting from the unrecognized object.
>>
>>-- David
>>
>>
>