From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mart Frauenlob Subject: Re: pinging and routing tables Date: Thu, 03 Dec 2009 09:48:05 +0100 Message-ID: <4B177B45.9000004@chello.at> References: <20091130175324.71602i65gacqf30g@webmail.oregonstate.edu> Reply-To: netfilter@vger.kernel.org Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20091130175324.71602i65gacqf30g@webmail.oregonstate.edu> Sender: netfilter-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: netfilter@vger.kernel.org sinkyh@onid.orst.edu wrote: > Hello all, > > I have, I hope, a simple question. From my understanding, by default > ping looks up up the IP address in the Linux kernel routing tables. What > happens if the IP is not in the routing table? Is the ping packet simply > dropped? > > The reason I ask this is that I have a few wireless devices for testing > purposes and I am using iptables to mimic a particular topology. Mainly > forcing the presence of only two possible routes from a source to a > destination over a series of hops. These devices have their own routing > protocol and basically routes are added/ deleted from the Linux kernel > routing tables based on metric measurements bla bla bla. That is just > fine and normal. > > However, since the devices are all in range of each other (due to space > restriction), if lets say the destination node IP is temporarily lost > from the source's routing table, for some reason the source is still > able to ping the destination directly. I assumed that if an IP is not in > the source's routing table that the outgoing ping would be dropped/ > ignored until the IP reappears. Not continue on ignoring routing tables.... > > Can anyone shed some light on this? > > Thanks for your help and suggestions. Hello, without being a network/routing guru, imho if there's not route to host X, you should see a message like 'no route to host'... Did you flush the cache? `ip route flush cache` - should clear it, so old records are removed. btw: bit offtopic here.... (not netfilter, tc, related) Hope it helps. regards Mart