The best way to explain IP classless is to explain how a router works with "no ip classless". Suppose you have a router with a static route configured to 10.1.1.0/24 out some interface and you also have a default gateway configured. Again, ip classless is disabled, "no ip classless".
A packet comes into the router destined for 10.1.1.2, the router looks at the routing table, sees the static route and forwards as expected. A packet comes into the router destined for 11.x.x.x, the router looks at the routing table, sees the default gateway and forwards as expected. A packet comes into the router destined for 10.10.10.1, you would expect the router to forward the packet via the default gateway. However, because the router is operting in "classful mode", the router drops the packet rather then using the default gateway. This is because the router is in the same classful network as the 10.1.1.0/24 network used for the static route. If the "ip classless" command was used, the dropped packet would actually be forwarded via the default gateway. There really is no reason not to use "ip classless" on all router configurations. Mike ""Hunt Lee"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Can anyone please explain to me what is "ip classless" used for? I looked > it up on the Caslow book, and it states that by enabling IP classless, it > allows one to override the contiguous subnet rule and allow the router to > look for the longest match beyond the listed subnets. > > But I still don't understand what it means? Can anyone give me some > examples? > > Thanks in advance. > > Best Regards, > Hunt Lee > IP Solution Analyst > Cable & Wireless Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30058&t=30056 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
