Wesley wrote: > > So there isn't a broadcast address for all /27 subnets?
I don't think sending to all subnets of a network is something that IP ever defined. > I > basically > understand that the last address of each subnet is reserved for > subnet > broadcast. I was just wondering if the broadcasting > architecture allowed for > all subnets to be broadcasted at once. And Mark, since you are > the only one > replying mind if you check out the CCO link in the original I hope Mark will answer too, but since we're the only ones talking now, I'll jump in. ;-) > post and tell me > your views on the issues that I have highlighted. I'll provide > the link > again > > http://www.cisco.com/warp/public/105/40.html I think the main thing to realize about the article is that it's a very strange case. Notice that the Asynch routers have a bunch of host-specific routes (/32). And then their E0's are configured with a /24 subnet mask, even though they probably should really be /26 to fit the network design. And then to make the problem happen they had to have a host misconfigured for /24 also and have it send a NetBIOS (or other) broadcast to x.x.x.255. I suggest that you set up a more normal situation in your lab and see if you can get the problem to happen. Perhaps TAC ran into a problem matching the scenario they describe. But is the problem reproducible under more normal condistions? (Perhaps TAC just made up the scenario too!? There are parts of it that aren't too believable. ;-) Please see a few more comments below. snip > > > > > > I was going thru this article about the effect of using the > all ones > > > subnet. > > > There are somethings that I'm still confused about. The > link is > > > > > > http://www.cisco.com/warp/public/105/40.html > > > > > > 1. In the first example, when host 195.1.1.24 sends a local > broadcast > > to > > > 195.1.1.255, will hosts attached to router 2's async lines > receive the > > > broadcast? No, the asynch lines are using /32. > > > > > > 2. OK, its a directed broadcast and router 2 looks up its I don't think Router 2 thinks it's a directed broadcast. The destination address doesn't match any of the /32 host routes, so Router 2 sends the packet out the default route. > routing > > table > > > and > > > forwards it out using the default route. Router 1 receives > the packet. > > I > > > believe the packet is forwarded out to all 192.1.1.x/26 > subnets, > > right? No, not all subnets. Router 1 has a specific route for subnet 192.1.1.192. (11000000 in the last octet). If a packet comes into that subnet, it's supposed to go to Router 5. See the static route that points to Router 5 (195.1.2.5). Now, Router 1 should recognize that the incoming packet is a directed broadcast for subnet 192 and not forward it if "no ip directed-broadcast" is configured, which is the default these days. > > > Will > > > Router 1 forward the packet back to Router 2? I hope not > > > No. > > > 2a. Another way of looking at it is router 1 thinks that it > is a > > > broadcast > > > only for subnet 195.1.1.192 and forwards it out only to > router 5. That's my interpretation too. > > Hmmm > > > .... > > > I'm definitely confused > > > > > > 3. Router 5 receives the packet from router 1. How will it > interpret > > the > > > packet? I'm guessing that the router sees it as a directed > broadcast Router 5, like Router 2, has a bunch of /32 host routes. The incoming packet doesn't match any of those, so Router 5 sends it out the default route. > > and > > > send it out via the default route. Is it normal that > routers forward a > > > packet out from an interface that it received on? Well, not too common, but it does happen sometimes. > As in its > received > > on > > > e0 > > > and forwarded out e0 as well > > > > > > 4. Once router 1 receives the packet from router 5, will it > forward > > the > > > packet out to all 192.1.1.x/26 subnets again or just to > router 5. Just to Router 5 > The > > > article did not detail this part and just specified that it > will > > bounce > > > between routers 1 and 5. It also says that routers 2 thru 4 > see the > > > 'broadcast' only once. The way I see it , if all subnets > receive the > > > broadcast then routers 2 thru 4 should receive the packets > as many > > times > > > as > > > router 5. > > > > > > I would appreciate all the help I can get. I know you gurus > can help > > me > > > out. > > > Thanks!! > > > > > > Wes > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=49050&t=48996 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
