I gather from reading through this exchange, and through the
document, that an update will be needed before the document
is put on the IESG agenda.
I don't expect to have any additional comments, and thus
suggest that you go ahead and update the draft to respond
to the Gen-ART comments. Let me know when the update
is available. For now I will change the state to "revised ID
needed".
Thanks, Ross
At 08:55 AM 9/12/2006 -0700, Arun Satyanarayana wrote:
Hi Elwyn,
Thanks much for the review. Please find responses inline.
Regards,
Arun (and co-authors)
==============================================================
Elwyn Davies wrote:
I am the assigned Gen-ART reviewer for
draft-ietf-ccamp-rsvp-restart-ext-05.txt. For background on Gen-ART,
please see the FAQ at
<http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html>.
Please consider these comments along with any other last call comments
you may receive.
Summary
=======
Generally an excellent document. I am not sufficiently familiar with
Thanks much.
the details of GMPLS RSVP to be sure that the technical specification of
state recovery are correct but nothing stuck out as missing or broken.
The one significant issue that I would suggest might need additional
justification/consideration is the implication that it should be used
after the control plane has suffered a security attack (s6, para 3).
RFC3473 specifies the original restart mechanisms for use after faults
and says nothing about security attacks. I would think that if a
particular node has suffered an attack that requires RSVP-TE restart,
there would be concerns about the whole chain of RSVP-TE nodes. I would
particularly worried about restarting an ingress node in these
circumstances. Would it be possible for a compromised node further down
the chain to force a restart and load inappropriate state? I don't know
if this is feasible but I'd want to be sure this couldn't happen.
Agree that the text is a bit open to interpretation. The basic surmise
here is that the RSVP agent was already protected against a security
breach (via means detailed in RFC2747). So, RSVP signaling state itself
is not compromised. However, due to some other part of the control plane
suffering a more penetrative attack, it is possible that the entire
control plane is restarted to clear such compromised state. The text
refers to RSVP state recovery under these conditions. Will re-work the
text to reflect this, if you feel this is more explicit in indicating
the case in question.
I have the impression that a graceful restart is going to create a fair
bit of traffic on a router with many paths set up. I didn't see any
suggestions for values of the Recovery Period and its relationship to
number of paths to recover - summarizing the total messages per path
involved in recovery might help give a handle on this.
Recovery times and actual number of messages are very dependant on the
following factors at least:
- The CPU speed on which the restarting as well as neighboring RSVP
agents reside on.
- The CPU availability during the Recovery Period (there may be routing
and/or other control plane being recovered during this period).
- Actual implementation specifics that affect the time taken to
communicate with the hardware to read current connection state:
one implementation may be able read the current connection and label
state via an intermediate software agent quickly; there could be
another implementation may choose to superimpose recovered state
on existing data-plane state and depend on errors if any to validate
state being recovered.
- Forwarding plane flush timers: ingress agents that reside on
packet-originating nodes would possibly have other timers on the
forwarding plane that dictate the upper bound on the Recovery Period.
As an example, it is critical to know that a GMPLS LSP used as an
IP nexthop interface is still available for forwarding - the
keepalive mechanism could be RSVP signaling state combined with
RSVP hellos.
These factors make such text far too open-ended to introduce in this
I-D. It is preferable to suggest values in a companion Informational/BCP
document (hopefully based on real numbers gathered from operational
networks).
Otherwise there are a few minor comments, mostly editorial.
Details
=======
s3, para 8: The name of the Capability object seems a bit general for
something which is very specific to the RecoveryPath mechanism. It might
be better to use something like RECOVERYPATH_CAP (to match with RESTART_CAP.
The nomenclature was chosen so since the object is carried in Hellos and
there are bits available for carrying other capability information in
the future. Will change the name if you feel strongly about this.
s4.2: Reserved bits SHOULD be ignored on receipt to allow extensions.
Thanks for catching this. Will change.
s4.2.1, para 1, 2nd sentence: s/All nodes/All such nodes/
Will change.
s4.4.1: The fact that a node is 'capable' of sending RecoveryPath
messages should not force it to announce and use this capability. I
think this should start something like: 'In order to announce that a node
is capable of sending RecoveryPath messages, it MUST include the
Capability object...'. This allows administrative disabling/disguise of
the capability.
Intent was the same. However, suggested text certainly carries the
sub-text better. Will change.
s4.4.2, para 3: '...it MUST treat the downstream neighbor..' - this is
not a sensible 'requirement'. I think it means that 'the receiving node
is able to expect that the downstream neighbor can send RecoveryPath messages'.
Ok. Will change "MUST" to "can".
s4.4.2, last para: Should something be said about any partial state that
has already been recovered when the transition happens? I don't know
enough about the details of the two processes to know if this could cause
problems with interactions between the two processes.
This is covered in s4.5.2.3 (Procedures on Expiration of Recovery
Period). The restarting node cannot make a decision reliably on partial
state until the expiration of the Recovery Period.
s5.2.1, para 2: This piece has got a bit garbled - apart from the
editorial, do you mean Srefresh mesages?
When the
restarting node does not desire the receipt of Reco=eryPath
messages, see Section 4.4.2, or, the selective transmission mechanism
defined in this section, ...
Will change to:
To indicate to an RSVP neighbor that selective transmission of
RecoveryPath messages is desired, a node MUST set (1) the S-bit in the
Capability object in all Hello messages it sends. When the restarting
node does not desire the receipt of RecoveryPath messages (see Section
4.4.2 - Procedures for the Restarting Node), or, the selective
transmission mechanism defined in this section, it MUST clear (0) the
S-bit in the Capability object if included in Hello messages.
s5.2.1, last para: As with s4.4.2, does anything need to be said about
partial state already recovered?
Handling of partially recovered state is covered in s4.5.2.3 (Procedures
on Expiration of Recovery Period). Since the SRefresh procedures are
only an optimization to the RecoveryPath procedures defined earlier in
the document, no explicit text has been included to handle partial
state.
Will include text if you feel strongly about this.
s6, para 4: s/minilmalized/minimized/
Thanks! Will do.
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