Post by thread:[PICLIST] [PIC] How about an open-source emWare li

I've heard from several sources that there is a user defined chunk of data that can be transmitted with each ping request and reply. You're right, and I phrased my earlier message badly. You can put whatever you want in the ping packet, but the problem is that the ping RESPONSE doesn't have any similar freedom - It has to include exactly the data that it was sent. I was assuming that you'd want to get some sort of information in the reply packet, although I suppose that getting any response can be interpretted as meaning SOMETHING, and you could do kludgy things like "you ping me and then I'll ping you back with the reply." Also, by definition, a ping is about the simplest protocol in the internet. And it is always implemented so even if you hit the wrong IP address, you get something back, and can tell if your connection is good (and you have the wrong IP address). I would expect error responses to ping to be even less likely to get through security-conscious firewalls than actual ping responses... BillW

I could be wrong here, but nothing in Ping restricts you sending different information back than was recieved. You can have up to 64K data, routers along the way aren't gonna dump a Ping packet return cause the data's different to the ping. Hence, as long as you have <64K (or whatever) of data, you're fine. Yes, the standard ping host will return the data you sent, but it's not exactly a requirement of the protocol. It'd be specced in the protocol cause what's the use of putting special data in if you don't know what will happen to it. You could use this for instance to check 2 outbound routes by sticking identifiers in the user data. But, if you use the first byte of the user data as a flag (e.g. you set it to 0x00, if it comes back 0xFF you just pinged a (insert product name here) gateway) and the next 63K are useful, new data. Nothing wrong with that in terms of the protocol, I'd say that's the sort of thing the user data's there for. Tom. {Original Message removed}