Oops. I mean to make the title say Ping to Directed Broadcast. The original title "Confused from London" wasn't meaningful, so I meant to do a good deed and change it, but changed it to the wrong thing. Hope you understand. :-)
(The meta-message is a strong recommendation that we all use titles with meaning to optimize the efficiency of the thousands of people reading the numerous messages per day on the list. Thanks.) Priscilla Priscilla Oppenheimer wrote: > > [EMAIL PROTECTED] wrote: > > > > Someone asked me a question which confused me:- > > If i ping a network broadcast from a host on a different > > network, which passes through a cisco router why do i get > > replies from certain devices. > > What are these "certain devices" that respond? > > Where are you running the ping from? What operating system? > What ping tool? How does the ping tool behave? Does it send a > single packet or try to be smart and send individual pings? > What is your topology? What is your config? Could there be a > misconfigured subnet mask so that devices don't agree on what > the broadcast address is? What do debug and protocol analyzer > traces show you? > > > > > The router has directed broadcast forwarding disabled. > > I thought the router would therefore drop the packet > > The router should not forward the packet onto the network in > question if you have "no ip directed-broad" configured on the > outgoing interface. I have verified that routers handle this > correctly, at least in my lab. > > However, I have seen some strange behavior with these routers > (running IOS 11.0, by the way). The routers respond to the ping > themselves! They don't forward, but they do respond, (regardles > of the configuration for directed broadcasts.) > > Here's the scenario where I've seen this: > > internetwork-----e0-Cisco router-e1----Ethernet LAN > > e0 > ip addr 10.10.0.2 255.255.255.0 > > e1 > ip addr 192.168.40.2 255.255.255.0 > > I ping from somewhere on the internetwork to 192.168.40.255. > With "no ip directed-broad" configured, the router doesn't > forward the packet, but it does respond to the ping. > > The reply comes from 10.10.0.2. Cisco routers accept this reply > and say that the ping succeeded. Windows 98 DOS ping does not > accept this reply (because it comes from 10.10.0.2 and not the > address that the ping was sent to). > > It is kind of strange that the router responds, so if your > scenario is similar, I can see why you ask the question. Of > course your scenario could be completely different too, and > there are probably numerous other reasons that you could be > seeing replies, depending on your config, tools, etc. > > _______________________________ > > Priscilla Oppenheimer > www.troubleshootingnetworks.com > www.priscilla.com > > > > Any thoughts > > Thanks > > -P > > > > > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57813&t=57780 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
