Re: Limited Domains:

On 13-Apr-21 10:20, Tom Herbert wrote:
> On Mon, Apr 12, 2021 at 3:10 PM Brian E Carpenter
> <brian.e.carpenter@gmail.com> wrote:
>>
>> On 13-Apr-21 08:52, Fred Baker wrote:
>>>
>>>
>>>> On Apr 12, 2021, at 1:51 PM, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
>>>>
>>>> In other words, a redefined flow label could be used pairwise between hosts that have determined that they are both members of a particular limited domain.
>>>
>>> Which would eliminate the use of the flow label by systems that are not part of that domain.
>>
>> No, it would create two sets of nodes: nodes using RFC6437 between themselves, and nodes using some other interpretation of the flow label between themselves. Ships in the night, really just like running IPX and CLNP on the same network. We used to do that a lot.
> 
> Brian,
> 
> The problem is that there's no code point that  discriminates between
> the different interpretations of the flow label. So in a limited
> domain the deployment of the new implementation must be perfect, lest
> there is at least one router that is inadvertently run with the legacy
> interpretation, then that router may process the flow label and ECMP
> per the standard leading to situations where packets of some flow are
> unexpectedly going over different paths. Since there's nothing in the
> packet that states what's happening, such problems can be really
> difficult to debug.

I completely agree. I was thinking about how to code this safely, and
it's a mess, especially if you want routers to detect it at line speed.

    Brian

> 
> Tom
> 
>>
>> I'm not advocating this, just pointing out that it's possible.
>>
>>    Brian
>>
>>
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> 