topic Re: tracert but cannot ping host in Operating System - HP-UX

tracert but cannot ping host

SM_3 — Tue, 17 Oct 2006 05:16:31 GMT

I had a case the other day where I could traceroute to a host but could not ping.

And I wondered why?

Can anyone explain?

Thanks.

Re: tracert but cannot ping host

Steven E. Protter — Tue, 17 Oct 2006 05:21:21 GMT

Shalom,

Based on the information provided there is no way anyone can explain this.

I can try and help with diagnosis:
1) Check the system nic light and see that the link light is lit.
2) Check the switch for errors, by looking at it or loggin on.
3) Check with networking and see if tracert has been diabled. Its pretty common to stop this servivce because it can be used for denial of service.
4) Check /var/adm/syslog/syslog.log

SEP

Re: tracert but cannot ping host

Hemmetter — Tue, 17 Oct 2006 05:38:14 GMT

Hi SM,

ping command sends "ICMP echo request" and receives "ICMP echo reply" these might be blocked.

Traceroute works different:
It sends some UDP-Packets with a ascending TTL and receives "ICMP time exceeded in-transit" while on the road or
"ICMP 192.151.52.241 udp port 33440 unreachable".

rgds
HGH

Re: tracert but cannot ping host

spex — Tue, 17 Oct 2006 06:22:44 GMT

Hi,

According to ping(1M):
The ping command sends ICMP Echo Request (ECHO_REQUEST) packets to
host once per second. Each packet that is echoed back via an ICMP
Echo Response packet is written to the standard output, including
round-trip time.

And according to traceroute(1):
This program attempts to trace the route an IPv4/IPv6 packet would
follow to some internet host by launching UDP probe packets with a
small ttl (time to live) or hop-limit then listening for an ICMPv4 or
ICMPv6 "time exceeded" reply from a gateway. We start our probes
with a ttl of one and increase by one until we get an ICMPv4 or ICMPv6
"port unreachable" (which means we got to "host") or hit a max (which
defaults to 30 hops and can be changed with the -m flag). Three
probes (change with -q flag) are sent at each ttl setting and a line
is printed showing the ttl, address of the gateway and round trip time
of each probe. If the probe answers come from different gateways, the
address of each responding system will be printed. If there is no
response within a 5 sec. timeout interval (changed with the -w flag),
a "*" is printed for that probe.

So, by default, ping sends ICMP packets and traceroute sends UDP packets. Moreover, the destination ports are different. A firewall could deny packets based on any of these criteria.

PCS