[ih] error detection

[Joseph Touch]

> On Oct 1, 2020, at 5:46 PM, Lawrence Stewart <stewart at serissa.com> wrote:
> 
> 
> 
>> On 2020, Oct 1, at 7:41 PM, Joseph Touch <touch at strayalpha.com <mailto:touch at strayalpha.com>> wrote:
>> 
>> 
>> 
>>> On Oct 1, 2020, at 3:22 PM, Lawrence Stewart via Internet-history <internet-history at elists.isoc.org <mailto:internet-history at elists.isoc.org>> wrote:
>>> 
>>> The properties that make a good end-to-end checksum are a little different:
>> 
>> Agreed, but...
>>> 
>>> ...
>>> * you’d like them to be <modifiable> if possible, so that a router can calculate a change to a checksum without recomputing the whole thing possibly based on erroneous data
>>> …
>> 
>> 
>> this particular requirement undermines the core of the definition of E2E.
>> 
>> Joe
> 
> The point of modifiable checksums is to preserve E2E. If you recompute the whole thing,

E2E doesn’t exist once you modify the packet. Period.

Any attempt to mod the checksum based on what you think you’ve changed could be in error - and could mask an error somewhere else as a result.

Joe