The MPLS WG Archive

[Ajay Simha <asimha@cisco.com>]

On Fri, 23 Nov 2001, Haseeb Budhani wrote:

HB>Hello folks,
HB>
HB>I'd like to get help on the following three issues:
HB>
HB>1. Is it possible to have different types of subojects -- IPv6 and IPv4
HB>-- in an ERO object ?? In case I missed it, the draft doesnt allow or
HB>explicitly forbid this ...

Haseeb,

Looks liked you missed it:

The contents of an EXPLICIT_ROUTE object are a  series  of  variable-
   length data items called subobjects.  Each subobject has the form:

       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
      |L|    Type     |     Length    | (Subobject contents)          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+

      L

         The L bit is an attribute of the subobject.  The L bit  is  set
         if  the subobject represents a loose hop in the explicit route.
         If the bit is not set, the subobject represents a strict hop in
         the explicit route.

      Type

         The Type indicates the  type  of  contents  of  the  subobject.
         Currently defined values are:

             1   IPv4 prefix
             2   IPv6 prefix
            32   Autonomous system number

HB>
HB>2. If local repair is in place, doesnt that basically counter the whole
HB>idea of having explicit routes ?? If CSPF or some other parallel
HB>mechanism is in place, when would one want to employ local repair ??

You could have explicit routes at the headend may be couple of them in
sequence.  The main point to be noted here is that explicit routes does not
mean no CSPF.  There could be checks against the TE-DB to ensure that require
bandwidth/attributes (affinity) is available along an explicitly specified
path.

The other assumption that local repair makes is that the repair is
"temporary".  It does send a PathErr back to the headend with error-code=25
(notification) and error-value=3 (tunnel locally repaired).  Upon receiving
such an error, the headend is at liberty to pick an alternate path be it
explicit or dynamic.

 HB>
HB>3. It would seem unlikely that a label subobject be present in the Route
HB>Record Object in a Path message. If there is a label subobject in a Path
HB>message, should this be flagged an error ??

Again this seems to be quite clear in the draft:

4.4.3. Processing RRO

   Typically, a node initiates an RSVP session by adding the RRO to the
   Path message.  The initial RRO contains only one subobject - the
   sender's IP addresses.  If the node also desires label recording, it
   sets the Label_Recording flag in the SESSION_ATTRIBUTE object.

   When a Path message containing an RRO is received by an intermediate
   router, the router stores a copy of it in the Path State Block.  The
   RRO is then used in the next Path refresh event for formatting Path
   messages.  When a new Path message is to be sent, the router adds a
   new subobject to the RRO and appends the resulting RRO to the Path
   message before transmission.

Hope this helps.

-ajay

HB>
HB>Any/all help will be greatly appreciated.
HB>
HB>

-- 
Ajay Simha
MPLS Deployment Engineer
IOS Technology Division
(919) 392-3141

"Study as if you were to live forever
 Live as if you were to die tomorrow"

 - Mahatma Gandhi