From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <482A9459.1010409@sysnetsistemi.it> Date: Wed, 14 May 2008 09:27:21 +0200 From: Francesco Dolcini MIME-Version: 1.0 References: <1210152122.32216.95.camel@gentoo-jocke.transmode.se> <2e59e6970805071916r701987fdx49bab341420ba2d@mail.gmail.com> <1210233718.32216.121.camel@gentoo-jocke.transmode.se> <2e59e6970805122010v50dcd5al101ae3466b897ad6@mail.gmail.com> <1210717793.5774.10.camel@collymore.citylink.co.nz> In-Reply-To: <1210717793.5774.10.camel@collymore.citylink.co.nz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Bridge] STP bug, loop not detetcted List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Dylan Hall Cc: bridge@osdl.org Dylan Hall wrote: > Most Cisco switches will generate a loopback packet (ethertype 0x9000) > at fairly regular intervals. Both the src and dst mac addresses are set > to the interface mac of the port emitting the packets. In the event a > loop exists in the network that hasn't been dealt with by (R)STP the > switch will receive the packet back on another of it's interfaces. In > the event one of the loopback packets does make it back to the switch > the port is error-disabled (I can't remember if it's the sending or > receiving port that is disabled). This mechanism is independent of > STP. > > UDLD also seems to have a mechanism to detect a port that is looped back > on itself. Again, independent of STP. > you can also add cisco loop guard to the list, but this is an improvement to standard STP, not a different protocol > Rather than modifying STP would it not be better to implement something > like the above as a standalone daemon? I agree, but it is also true that if we can improve STP without breaking compatibility there is no reason to not do it.