No need to cc me, I read the list. On Sun, Aug 13, 2000 at 09:10:02PM -0400, Alessandro Ghigi wrote: > > > On Sun, 13 Aug 2000 [email protected] wrote: > > > On Sun, Aug 13, 2000 at 03:41:58PM -0400, Alessandro Ghigi wrote: > > > > > > There are some addresses I cannot ping, while I can access them with > > > Netscape, ftp or finger (depending on the type). I can't figure out what > > > is difference between these addresses and the ones which I can ping > > > succesfully. > > > > This may be a result of firewalling at the remote site. It's possible > > to disable ping replies. I believe through ICMP accept/deny rules, > > though I'm new at this. > > But if I ping these addresses (e.g. www.netcom.com, ftp.de.debian.org, > xxx.sissa.it) from > the account I have on the server (the same server to > which I connect via PPP) the addresses respond. Therefore I guess it's my > fault. Another strange thing (strange for me, I mean) is that when ping > knows and displays the IP corresponding to the address (but does nothing > more).
Firewalling is specific to host. If a host is firewalled to reject icmp
type 0 requests, it won't respond to a ping. The firewall is at or near
the remote host, net you and your ISP. This means you *can* ping some
hosts:
+---------------------+ +----------------+
,--> | FW pass icmp type 0 | ---> | pingable host |
/ +---------------------+ +----------------+
+---+ +---+ / +----------------------+ +----------------+
|You| ===> |ISP| ----> | FW BLOCK icmp type 0 | ---> | unpingable host|
+---+ +---+ \ +----------------------+ +----------------+
\ +---------------------+ +----------------+
`--> | FW pass icmp type 0 | ---> | pingable host |
+---------------------+ +----------------+
...the other thing that's happening is DNR -- domain name resolution.
ping isn't looking up the address for the server you're trying to reach,
it's quering your local (or remote) BIND servers. The response is
likely coming from a cached version of this database either on your own
system or at some other point between you and the remote server.
--
Karsten M. Self <[email protected]> http://www.netcom.com/~kmself
Evangelist, Opensales, Inc. http://www.opensales.org
What part of "Gestalt" don't you understand? Debian GNU/Linux rocks!
http://gestalt-system.sourceforge.net/ K5: http://www.kuro5hin.org
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