[vlc-devel] Streaming wizard issues

jpd at videolan.org jpd at videolan.org
Mon Nov 30 10:50:12 CET 2009

On Mon, Nov 30, 2009 at 10:15:06AM +0100, Marian ??urkovi?? wrote:
> 1) multicast doesn't get beyond a router which is not *explicitly*
> configured to route it. Any local network is effectively isolated by
> this even without TTL=1 hack

That's still no reason to set up this and the next network for instant
flooding the moment it does get enabled. If ``the user'' does that
knowingly, it is their doing. If the same user unwittingly does it
because we set the default unreasonably high, it is our doing.

> 2) problem with TTL=0 happens even on largest internet-grade routers like
> Cisco 7600, which are certainly well capable of routing multicast

Apparently not, but then it also was Cisco software that would duly
decrement-by-one-and-propagate packets incoming with TTY=0. A big name
is no guarantee of well-behavedness.

> 3) usage of TTL scoping is discouraged by latest RFCs, I don't have time
> to look it up ATM but courmisch can certainly provide a reference to you,
> since he already changed SAP announcer to *not* use TTL scoping quite some
> time ago. TTL scoping sucks big time, it shouldn't be used anymore.

Then at most default to the system-wide default. Do provide references
when you do have the time. But I think you are mixing up ``providing
a safe default'' and ``depening on TTY=N for your production use'' here.

For the latter, non-TTY means may very well be preferrable. But for
the former, in case of casual or ignorant over-reach, network fault
isolation benefits from predictability, and TTY=1 provides that, there
arbitrarly high TTY does not.

The default in VLC isn't ment for production, but to provide a sane
default, and in the case of multicast with its flooding potential,
limiting the damage to the local broadcast domain and its gateway(s) is
much more sane than flooding everywhere.

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