RE: Proposal for changing how IPv6 Hop-by-Hop Options are processed

[Ron Bonica <[e-mail]>]

Folks,

The following are a few things we can all agree on:

- The maximum length of an HBH Options header is 2,048  bytes.
- A source node can encode hundreds of options in 2,048 bytes.
- Given today's technology, it would be impractical to design an ASIC that can process hundreds of options.
- When an ASIC encounters a packet with more options than it can process, the best thing it can do is to drop the packet

Having established that hundreds of options are too many, we are left with the following questions:

- Should each node determine the maximum number of options that it can process, or should there be a global maximum?
- If there should be a global maximum, what should that maximum value be?

If we leave each node to determine the maximum number of options that it can process, source nodes will need to discover the maximum number of options that can be used on each path. This should remind us of PMTU Discovery. We have all seen that movie. It has  a very sad ending.

If we can agree that each node should support at least a global maximum number of HBH options, we are faced with the following dilemma:

- If we pick a constant that is too small, we may not be able to support future use-cases
- If we pick a constant that is too large, low-cost processors may not be able to support it

I think that even low-cost processors can handle 2 or 3 options without blowing their processing budgets. Maybe we should consider a global maximum value somewhere between 1 and 4?

                                                                                               Ron



Juniper Business Use Only

-----Original Message-----
From: ipv6 <[e-mail]> On Behalf Of Tom Herbert
Sent: Friday, December 4, 2020 10:55 AM
To: Gorry Fairhurst <[e-mail]>
Cc: Haoyu Song <[e-mail]>; IPv6 List <[e-mail]>; Bob Hinden <[e-mail]>
Subject: Re: Proposal for changing how IPv6 Hop-by-Hop Options are processed

[External Email. Be cautious of content]


On Fri, Dec 4, 2020 at 2:34 AM Gorry Fairhurst <[e-mail]> wrote:
>
> I see lots of thoughts - all of which might help see us through 
> towards some conclusions.
>
> Just on (1). Whether one HBH option si enough, might depend on the 
> use-case.
>
Gorry,

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