Re: [v6ops] Flow label setting [WG Doc? draft-gont-v6ops-ipv6-ehs-packet-drops]

[Brian E Carpenter <[e-mail]>]

On 15/03/2016 11:32, Tom Herbert wrote:

...
> - Linux (e.g. Android will): sets the flow label for new connections
> (TCP or connected UDP socket) using prandom_u32 (pseudo random
> number). The flow label for a connection may change if the connection
> is failing in hopes of finding a better route

In that case, it really doesn't matter as far as ECMP or load balancing goes
if the flow label changes, since the path will be changing anyway.
(OK, it might matter for server load balancing at the destination,
but that is a corner case that has to be dealt with regardless.)

> -- either the networking
> stack detects a bad route (i.e. TCP is retransmitting) or userspace
> can request a route change if it has information about path quality.
> So flow labels are not necessarily persistent which probably makes
> flow label filtering a bad idea

It's a bad idea, period. If you are trying to detect malicious traffic
you will need DPI anyway.

> at least if persistence for the
> lifetime of a connection is required for that (see
> http://www.maths.tcd.ie/~dwmalone/p/ec2nd05.pdf). For cases with no
> connection state (unconnected UDP, forward and encapsulate), the flow
> label is generated by parsing the packet to determine a hash based on
> L3/L4 information.
> 
> - Windows: I believe you mentioned that Windows 7 doesn't seem to have
> support for setting flow labels.

I couldn't find anything. Presumably it can be done by apps through the
Winsock API, but that isn't very useful.

> Maybe someone from Microsoft can
> clarify this and let us know what the prospects are for getting flow
> label support.

Please.
   Brian