-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Matt
Gravlin
Sent: Saturday, August 26, 2000 9:49 PM
To: [EMAIL PROTECTED]
Subject: Re: ip classless ?
The ip classless command is used when setting up default routes. Cisco
routers (classful by default) expect a subnet mask when entering your static
ip route commands, so when you are setting up a default route, you must
specify ip classless, since no remote subnets will be in its routing table
for default routes.
--------------
CL: this is not exactly correct. I took the following from the documentation
home page, configuration guides. In this case 12.1, but it applied to
earlier IOS versions as well.
Classfull versus classless behavior of Cisco routers remains a bit
confusing, and therefore highly misunderstood topic. The IP Classless
command ( or classless behavior ) is on by default in the newer IOS, anyway,
as noted below. It operates in case default routes do not exist. If there
are default routes, then the behavior may or may not be necessary, depending
upon other factors.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c
/ipcprt1/1cdipadr.htm#1001090
watch this nasty word wrap
By default, classless routing behavior is enabled on the router. When
classless routing is in effect, if a router receives packets destined for a
subnet of a network that has no network default route, the router forwards
the packet to the best supernet route.
In Figure 1, classless routing is enabled in the router. Therefore, when the
host sends a packet to 128.20.4.1, instead of discarding the packet, the
router forwards the packet to the best supernet route.
If you disable classless routing, and a router receives packets destined for
a subnet of a network that has no network default route, the router discards
the packet. Figure 2 shows a router in network 128.20.0.0 connected to
subnets 128.20.1.0, 128.20.2.0, and 128.20.3.0. Suppose the host sends a
packet to 128.20.4.1. Because there is no network default route, the router
discards the packet.
To prevent the Cisco IOS software from forwarding packets destined for
unrecognized subnets to the best supernet route possible, use the following
command in global configuration mode:
no ip classless Disable classless routing behavior.
===============
Matt
""Yee, Jason"" <[EMAIL PROTECTED]> wrote in message
859B90209E2FD311BE5600902751445D2E7CF4@LYNX">news:859B90209E2FD311BE5600902751445D2E7CF4@LYNX...
> hi ,
>
> Anyone knows why when we use RIP or IGRP routing protocols and we have a
> default network command entered , we need to include ip classless?
>
> Any form of input will be greatly appreciated
>
>
> thanks
>
>
> Jason
>
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