[clug] Re: Determining availability of a remote machine

Kim Holburn kim.holburn at anu.edu.au
Fri Apr 4 23:13:01 EST 2003

At 10:04 PM +1000 2003/04/04, Jepri wrote:
>On 2003.04.04 18:53, Michael Still wrote:
>>On Fri, 4 Apr 2003, Jepri wrote:
>>	"The echo service sits on port 7, and replies back with
>>	you said, just like a senile grandmother" [9]
>My grandmother just says 'oh, really?' all the time :)
>The original discussion was a request for a way to test servers, without using ICMP (which you gave a good summary of).  Under those circumstances I thought that pointing out a user level, non ICMP alternative was a good idea.  I was completely wrong about it being part of a ping standard though, it's just that I've heard (and used) the phrase 'tcp ping' enough times for it too seep into my idea of 'ping'.

I think tcp ping is something like what nmap can do and is unrelated to the "small services" (echo chargen, daytime, etc.)  It's more along the lines of trying to open a tcp connection and analysing the responses.  I could be wrong about that though.  So few boxes these day have tcp echo on that I can't see it being useful.  It never really was.

>A reasonable firewall administrator should let port 7 requests go out, but I'd be blocking it incoming.
>Intruigingly enough, it is enabled by default on my Debian box.
>>I can only imagine that this is a deliberate attempt to offend Kim,
>>who is
>>regularly helpful on this mailling list. Would you care to rephrase
>I do hope Kim didn't take that as a personal attack, because it wasn't.

Not at all.

> Kim was first in with the best answer
>(as I'm sure s/he knows),


>and I do appreciate Kim's input on the mailing list.  I'm currently looking up the programs mentioned in that answer, and they look cool (and don't use ICMP).

I have a copy of lft but I haven't had any time to work out why it doesn't work yet. 

I assumed that when Michael said "can't use ICMP" he meant he couldn't use echo request.  ICMP is part of all IP traffic.  Things won't work properly without it.  Most modern routers might stop ping (ICMP echo request) but they won't stop ICMP messages that are part of tcp unless they are seriously broken. 

>It was just a frustrated comment that had little to do with the people in the discussion.

heh heh.

>>Yours in a ongoing effort to learn more about everything,
>Me too,

Kim Holburn 
Network Consultant - Telecommunications Engineering
Research School of Information Sciences and Engineering
Australian National University - Ph: +61 2 61258620 M: +61 0417820641
Email: kim.holburn at anu.edu.au  - PGP Public Key on request

Life is complex - It has real and imaginary parts.
     Andrea Leistra (rec.arts.sf.written.Robert-jordan)

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