The MPLS WG Archive

[afarrel@movaz.com]

Title: RE: What exactly constitutes the State info in FT-LDP and what do we mean by "Securing the message" ??

Hi Aditya,

Sorry for the break in communications, I have moved company and am now at Movaz Networks.

> The question I had asked Adrian was:-- "Could
> you explain what you exactly mean by "state
> and information related to the previous
> incarnation of the session "

> In section 3.4 of your draft you say that
> "If either LDP peer sets the FT Reconnect Flag to 0, or omits the FT
>  Session TLV, both LDP peers MUST release any state information and
>  resources associated with the previous instantiation of the LDP
>  session between the same LDP peers, including FT label state and
>  Addresses"
> Could you please tell me as to what specifically
> constitutes the "state information and resources" ??

Well, the most obvious resources are labels.
If you're doing CR-LDP there may be bufferage, bandwidth etc. to release.  Basically any resources in the switch that were reserved or utilized in support of the LSPs established using the previous instantiation of the LDP session.

Additionally, there will be internal control blocks and the like that your code is maintaining for the session and associated LSPs.  These should be freed or reset at this time.

> Secondly in Section 4.2 of your draft you write
>   "When an LDP Peer receives a message containing the FT Protection TLV,
>   it MUST take steps to secure this message (or the state information
>   derived from processing the message).  Once the message is secured,
>   it MUST be ACKed.  However, there is no requirement on the LSR to
>   send this ACK immediately."
> What do you exactly mean by the term "SECURED".
> ....obviously it does not mean "PROCESS" the message ?
> So what does "secure this message" mean ????

Well it COULD mean processed.

The minimum requirement is based on the understanding that once the message has been ACK'ed the message-sender will assume the message receiver has already or will eventually process the message.  This means that the message sender does not need to retransmit the message in order to achieve the desired effect.

The only let-out for this is that the session can be re-established saying that _no_ state information was preserved.  This will ensure that both peers have the same view of the LSPs between them.

Regards,
Adrian
--
Adrian Farrel
Movaz Networks Inc
afarrel@movaz.com