Re: [mpls-tp] [mpls] [PWE3] [AHMPLS-TP] Re: pollondraft-he-mpls-tp-csf-03.txt

[Ben Niven-Jenkins <[e-mail]>]

On 2 Dec 2010, at 05:04, Yuanlong Jiang wrote:
> ----- Original Message ----- From: "Eric Osborne (eosborne)" <[e-mail]>
>> From: [e-mail] [mailto:[e-mail]] On Behalf
> Of
>> Yuanlong Jiang
>> 
>> Typically, IP will only detect a failure in a time scale of minutes.
> 
> I must not understand the point you're making.  For one thing, BFD is
> quite often configured to detect failures in significantly less than a
> minute.
> [JYL] The question is: Can we assume BFD is universally deployed for IP and PW?
> If the answer is yes, then CSF is not needed, even for the PW application.
> 
>> That is one reason why MPLS-TP OAM and Protection & Switching is
> needed.
> 
> What are others?
> [JYL] Maybe you'd better refer to RFC 5654 for a comprehensive reqs :)
> 

Let's take a step back for a moment. Your original premise is wrong IMO. The need for OAM, protection & switching is MPLS-TP is not predicated on the fact that IP networks can't re-converge quickly enough.


>> I am not sure which mechanism in MPLS provides the CSF-like
> capability,
>> could you give more hints?
> 
> Even regular IGP/LDP hellos (no special tuning, no BFD) very frequently
> are configured to detect failures in far less than "minutes".
> [JYL] Not sure this can be used to indicate the failure of  IP service.
> Even so, do we need to firstly determine what protocol is carried and then decide which mechanism could be used?


The CSF draft covers two cases:
- PWs
- LSPs (and by implication the three clients supported by LSPs, namely IP, PWs and other LSPs)

PWs have a mechanism already and the CSF draft acknowledges that.

LSPs have BFD and other tools to detect failures.

IP has a bunch of mechanisms e.g. IGP hellos if you're building an IP network or various keepalive mechanisms if you're layering IP tunnels on something else.

The premise of the draft is "This document defines such a MPLS-TP OAM tool as Client Signal Fail indication (CSF) to propagate client failures and their clearance across a MPLS-TP domain" based on the fact that "the client layer OAM functionality does not provide an alarm notification/propagation functionality"

For the three possible clients of MPLS-TP, the second sentence I quote above does not hold true and therefore the draft is not needed.

However, if I am wrong and the draft really is needed it should be straightforward for someone to post a description of a practical deployment use case where the existing IP mechanisms are insufficient and the CSF functionality is required in MPLS-TP to proxy for the lack of client level functionality.

Ben