On Tuesday, July 30, 2002, at 09:18 , Jean-Luc BEAUDET wrote:
[..]
> Yu have to be aware that, generally, if yu go out the local network
> FireWall
> block ICMP packets...
>
> The ping statement is not a good evidence test...
excuse me while I giggle... a bit here.
I have no idea how many times I have had to explain to
software engineers,
No, the Firewall will not allow you to
ping through it, so please stop trying
to automate if your cool far webSite has come back up...
while on the other side of the game, half the reason I
have built most of the network monitoring tools that I
have rests upon the impoliteness of various 'network
interface cards' to be ever so polite as to acknowledge
that they were in receipt of an ICMP packet, while
the rest of the hardware/kernel was 'toes in the air'
unable to do SQUAT.
At best one knows with some certainty that if one
has 100% packet loss on a 'ping check' that either
the remote host is down, or the network is scrambled
between the monitoring host and the host being pinged.
{ nothing ever more enjoyable than a router that has
decided that the sub-net you want should go out the
left side, when the sub-net itself is wired out the right
side of the box... makes for a whole lot of fun finding
that bit of 'logical misdirection'.... }
But I think we all start with the simple 'can I ping
far host' approaches to network monitoring....
Since clearly IF you can ping far-host, there is a chance
that you can then proceed along to the rest of the tests
about whether the next layer up the stack is gonna work...
ciao
drieux
http://www.wetware.com/drieux/pbl/
--------------
Uncle Drieux Says:
never NFS mount the code that does the
NFS mount checking....
Nothing like having the 'monitoring suite'
branch and hang waiting for the NFS server
to return the code you need to validate that you
can effectively talk to the NFS server
Since that way allows one the warm feeling that all is
well, because no error message has been generated....
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