check host alive

[Andreas Ericsson]

Andy Shellam (Mailing Lists) wrote:
> 
>> Most systems have 64 as default TTL, otherwise you're right. There are
>> two
>> "variants" of "Time to live exceeded". One is where the there are more
>> hops
>> to the target than the TTL set in the packet. This is known as "Time
>> to live
>> exceeded in transit".
>>   
> 
> Hmmm something rang a bell when you've said 64, however I've just got a
> completely different answer to both of our theories!
> On Windows, the TTL is set to 127, on my FreeBSD 6.1 box it's set to
> 246, and on Fedora 5 it's 243.
> 
> The TTL displayed in the ping output, is this the same TTL as what we're
> both referring to?
> 

No, that's the TTL in the response packet, which will be "defult TTL of
host sending ICMP_ECHOREPLY" minus "hops between pinged host and self".
The TTL on the outgoing packets are, by default, 64 on *BSD and Linux,
128 on Windows and HP switches/routers, 255 on Cisco and 3Com stuff...

64 is usually as high a TTL as one can stomach for most practical
reasons (I reach Australia with 36 hops from Sweden).

On Linux, the default TTL can be accessed through
/proc/sys/net/ipv4/ip_default_ttl

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys - and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
Nagios-users mailing list
Nagios-users at lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/nagios-users
::: Please include Nagios version, plugin version (-v) and OS when reporting any issue. 
::: Messages without supporting info will risk being sent to /dev/null