(accidentally hit send too soon – please ignore previous email)
Greg –
Thanx for responding to my comments.
Looking at the revised draft, I confess to being somewhat confused. Please help
me understand.
1)The text in Section 4.2 is unchanged. It still says:
“The BFIR generates the My Discriminator value for each multicast flow
and advertises it to the expecting BFERs, which is indicated by the
Bitstring and the BIFT-id,”
This is not consistent with the revised format of the IGP advertisements.
2)More importantly, looking at the revised IGP advertisement in Section 4.2.1,
we have:
No. of octets
+-----------------------------+
| Type = TBD3 | 1
+-----------------------------+
| Length (multiple of 2) | 1
+-----------------------------+
| BIFT-id | 2
+-----------------------------+
| My Discriminator(s) | 4 * Number of My Discriminator(s)
: :
+-----------------------------+
I do not understand the relationship between the multiple discriminators and
the single BIFT-id.
Don’t you use the same Discriminator for all of the BFERs for a given
multipoint path??
Previously the bit string presumably identified the set of BFERs.
Now you have multiple discriminators.
I am frankly lost here.
??
Les
From: Greg Mirsky <[email protected]>
Sent: Tuesday, July 23, 2024 10:56 AM
To: Les Ginsberg (ginsberg) <[email protected]>
Cc: [email protected]; [email protected]; [email protected]
Subject: [Bier] Re: Call for review for draft-ietf-bier-bfd
Hi Les,
thank you for your thoughtful questions and comments; much appreciated. The
authors discussed them and we propose updates that are reflected in the
attached copy of the working version and highlighted in the diff. Although the
BitString information is useful for a tail, it, for the purpose of reporting
defects to the head of the multicast tree, is optional. In fact, the identity
if the BFIR and its unique My Discriminator value are sufficient to correlate a
notification from the tail to the appropriate BitString set.
Your comments on the updates are most welcome.
Regards,
Greg
On Sun, Jul 7, 2024 at 10:15 PM Les Ginsberg (ginsberg)
<[email protected]<mailto:[email protected]>> wrote:
Folks –
I apologize for the lateness of my comments – I don’t consistently track BIER
WG. Some of what I say below would certainly have been more beneficial if
provided earlier.
Nevertheless..
Regarding the proposal for new IGP Extensions for advertising BIER BFD
information:
I am troubled at the idea of having the IGP advertise information which
includes the BIER Bit-String representing the relevant BFR-IDs. This string
(defined in RFC 8296) can potentially be up to 4K bits (512 bytes) long.
This is a lot of information for the IGPs to carry – and is particularly
troublesome for IS-IS where it exceeds the carrying capacity of a single TLV
(max 255 bytes).
As a more minor point, the presence of the RESERVED field is inappropriate for
IS-IS. This is commonly done in OSPF to preserve 4 byte field alignment, but
this is useless in IS-IS and only serves to bloat the TLV size unnecessarily.
In a larger context, the only previous use of the IGPs to advertise BFD
discriminators that I am aware of was done in support of S-BFD (RFC 7883). To
my knowledge, implementations have not made use of this extension – perhaps in
part because assignment of discriminators based on information in an IGP
database has not proved appealing – which calls into question why we should do
this here.
NOTE: I am happy to hear feedback from others that RFC 7883 is in fact being
used.
Finally, I ask whether any implementation of this draft – even as a POC – has
been done? If so, what has been learned?
In general, I am concerned that in the absence of implementation experience we
may be standardizing things prematurely.
Thanx for listening to my very late remarks.
Les
From: [email protected]<mailto:[email protected]>
<[email protected]<mailto:[email protected]>>
Sent: Tuesday, June 25, 2024 12:25 AM
To: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Subject: [Bier] Call for review for draft-ietf-bier-bfd
Hi,
The draft-ietf-bier-bfd passed last call in BIER WG.
We'd like to get more review in BFD WG:
https://datatracker.ietf.org/doc/draft-ietf-bier-bfd/
Comments and suggestion welcomed, please send your comments before 9th, July.
And please volunteer if you want to be the shepherd of this draft.
Thank you!
Best regards,
Sandy
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