In article <email@example.com>,
“Igor Kovalenko” <firstname.lastname@example.org> wrote:
This is confusing. For what I know (I can be wrong of course, especially
Yes it was. Sorry for the confusion. Here is some more information that
may help clarify.
- There is no way to tell if some box is listenig to a port other than to
try to establish a connection or send a packet.
I understand this. I have a network tool, AGNetTools, which does a “port
scan” at an IP number of my choosing. The tool reports back which TCP
and UDP ports at which that IP listening. This same tool will also do a
“service scan”, whereby you tell it an IP range and a port number and
the tool tells you which IP numbers are listenting to that TCP or UDP
port. I don’t know the magic by which it determines this information,
but there it is. Presumably, it tries to make a connection and reports
whether it succeeds.
- DHCP servers do not advertize anything, they just reply to incoming
requests. DHCP clients send their requests either through broadcast or to
specific pre-configured IP. If no server replies, DHCP client just times out
and Windows complains.
…or MacOS assigns a default IP number, or something else specific to
the OS and TCP/IP stack.
Given that, your box can’t ‘look like’ anything to your subnet if it does
not actually serve clients’ requests. What do you mean by ‘went insane’? Did
Windows complain about no DHCP server or did it get bogus IP?
The raw data I have is that, overnight, all the DHCP machines in the
office failed to get new valid IP addresses, as if the DHCP server had
gone away or given bad addresses. The DHCP server was not misconfigured
and was working properly.
After a hard reset of the network, I did a service scan of the network
and found two machines which respoded to port 67/UDP (the DHCP server
address), the DHCP server and the QNX6 box. I then did a port scan on
the QNX6 box and the tool reported that all tested UDP ports were
“alive” (however the tool tests it).
After taking the QNX6 box off the network, the problem has not recurred
in 48 hours. I’ll admit that this is not iron clad evidence of a
problem, but I find it odd that the QNX6 box responded to all UDP ports.
No other box on the network did that.
Any further clues?
Thanks for your help,