Re: possibly related draft

Hi Joe,

Joe Touch wrote:
> I am concerned about the use of some of this inferred information from 
> the link layer or transport layer to decide connectivity at the network 
> layer.
> 
> Notably, failure of TCP to make forward progress - e.g., lack of ACKs - 
> is not an indication of a network layer connectivity failure. It can be 
> a deliberate decision of the TCP implementation to limit processing 
> associated with a connection, or can represent a security firewall being 
> enabled.
> 
> Similarly, we've had related dicussions in TCPM regarding the use of 
> ICMP unreachable messages to tickle more rapid attempts to use alternate 
> addresses, e.g., for v4/v6 selection. Unfortunately, these messages, as 
> noted, are not secure, and so relying on them presents a DOS 
> opportunity; it is not clear that there is a significant benefit in 
> 'believing' these messages that is not undermined by this lack of security.
> 
> Although it may be useful to consider direct evidence of connectivity, 
> e.g., linkup/linkdown interface notification via an API, it is not clear 
> yet that there is a protocol-related variant that can be appropriately 
> applied, IMO.

At this stage there's no work done within DNA WG on APIs but we're
looking at getting indications of local connectivity from L2 into L3
within DNA WG.
Similar work has been going on with DNAv4 in DHC.

I'd guess that once the DNA system is able to indicate that an IP
configuration (addresses,local routers) is invalidated, or had
a connection discontinuity (e.g. link-layer only base station change)
This information could be passed to the upper layer protocols or IP
subsystems, in a similar fashion to a subset of the trigtran work
(but with only adjacent layer violations).

Hysteresis and security of the change discovery would probably exist
within the DNA subsystem, but information about trust could be
passed around too.  I'm not proposing this as a work item for DNA,
but it's intertesting for that group to see what people are really
interested in.

Please tell me if this is the right path to look down for local
connectivity indications (or not).

Greg D.