Re: RE : [lwip-users] Questions about LwIP KEEPALIVE...

[David Empson]

Hi Frédéric

On Monday, February 19, 2007 10:19 PM, "Frédéric BERNON" 
<address@hidden> wrote:
> You're right, if the protocol got a specific message to poll the peer, this 
> is not a problem. But some protocols
> don't get them. Sometimes, we can found some workarounds. By example, with 
> Telnet : you can send a
> "<SPACE><BACKSPACE>" to peer to force a communication checking, but, it can 
> only work with my
> own telnet clients/servers. More, when you port some sources, you need to 
> adapt them, and it's not very
> always simple.
>
> To my point of view, porting applications on LwIP at socket layer would 
> need to do only very limited
> modifications on applications. I thought that enable to customize default 
> values with lwipopts.h seems to be
> in the "lwip spirit". If doing this is "too specific", ok, I will do it 
> only in my own lwip copy.

Even if you only do it in your copy of LWIP, I can see two problems with 
modifying the LWIP keep-alive timer:

1. It only affects one direction. The other direction will still be sending 
slow keep-alive packets (unless you have sufficient control over the other 
end as well).

2. If you are running multiple protocols or applications over TCP/IP, a 
global change in the keep-alive timer may not be suitable for all 
applications. Even if you are running the same protocol over multiple 
connections, you might need different keep-alive settings for each 
connection (e.g. a LAN connection vs a cellular data connection).

> I just look the DNP protocol. Is it a very used protocol? Do you an 
> overview about it (send me a private email if you can)...

(replied privately to this part)