JiangXingFeng wrote:
Yes, I agree some sort of keep alive is needed to detect liveness on
these connection. We also need to be able to deal with receiving a TCP
RST for the TLS connections.
Why should the keepalive be at the peer layer rather than using STUN?
It seems like that mechanism is well-understood and lightweight. Now
detecting failure is a slightly different question (and very hard, in
general), but in general it seems to me that the stun keepalives solve
this.
(You're right that the draft doesn't say that you should be using STUN
keepalives over TCP/TLS. But assuming it did, do you think it needs
something else at the peer layer?)
IIRC, STUN keepalive is used to make the middle-box, such as NAT, firewall
to keep the state valid. It is often sent within a short interval. I also
think it is a good alternative to carry out the keepalive. But to me, there
are two questions:
1. For a direct connection without the involvement of the middle-box, the
STUN keepalive is not needed any more;
One of the motivations for using it is that the device does not need
have an oracle that tells it whether it is in such a situation or not.
As ekr points out in another email, periodic UPDATEs can serve the same
purpose. Doesn't matter what the message is except for UDP where using
STUN to detect rebinding is very useful.
2. Although RELOAD requires all nodes support STUN, but P2P implementation
and STUN library are separate modules and it requires the modification to
the current STUN implementations to let the STUN notify other applications
on the same host what's happening about the connection in question. Do we
need a standard interface or just leave it to implementation?
We use our implementation of STUN in multiple components. STUN is
small enough that you could just integrate a custom version in each
protocol. You can also write something that's pluggable and use the
same implementation with different components. I think this is just an
implementation question.
Bruce
On the other hand, I think keepalive mechanism could be easily extended to
distribute some state changes about peer's information to its neighbors. SEP
makes use of the keepalive to realize a light-weight service discovery
mechanism.
-
JiangXingFeng
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