Date: Thu, 4 Sep 1997 23:15:18 -0400 From: Matthew Hunt <hunt@mph124.rh.psu.edu> To: Michael Richards <026809r@dragon.acadiau.ca> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Ping bug? Message-ID: <19970904231518.50368@mph124.rh.psu.edu> In-Reply-To: <199709050210.XAA19228@dragon.acadiau.ca>; from Michael Richards on Thu, Sep 04, 1997 at 11:10:24PM -0300 References: <199709050210.XAA19228@dragon.acadiau.ca>
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On Thu, Sep 04, 1997 at 11:10:24PM -0300, Michael Richards wrote: > I have an interesting problem with ping. I don't know if it is a bug or > not. I vote not. :-) > The man page says that the -Q switch will shut it up when it comes to error > messages. It says it won't display ICMP error messages. That doesn't mean that it won't print other diagnostics. > ping: sendto: Host is down > ping: wrote lib226-1.acadiau.ca 64 chars, ret=-1 > > According to the man page, it shouldn't give me any errors. Even funnier, it > seems to behave correctly if I just start off pinging it once. As soon as I > try pinging a second time in a row, it spits out these error messages... When you first start ping, and the destination is on the local network, your box sends an ARP request to find out the destination's hardware address. If the destination is down, no responses are going to come back, so ping doesn't print anything. After a certain amount of failed ARP queries, your machine will add an entry to the routing table saying that the host is unreachable, in order to keep from sending out further ARP queries. Ping will display this "host unreachable" error; it is not the result of receiving an ICMP error packet. The "host unreachable" route is short-lived, and looks like this: Destination Gateway Flags Refs Use Netif Expire 128.118.126.2 link#1 UHRLW 0 10 ed0 14 ICMP error messages include things like "TTL exceeded" and other "unrechable" messages delevered by a router (i.e. the destination is not on the local network). Here's an example: mph124:~$ ping 147.160.223.15 PING 147.160.223.15 (147.160.223.15): 56 data bytes 36 bytes from 205.219.15.229: Time to live exceeded Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 5400 d1dd 0 0000 01 01 7652 128.118.126.83 147.160.223.15 Adding "-Q" would suppress displaying that ICMP error, received from the router at 205.219.15.229. Hope this helps. -- Matthew Hunt <mph@pobox.com> * Think locally, act globally. finger hunt@mph124.rh.psu.edu for PGP public key.
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