When a router looks for a route to a destination, it has two ways of
doing it:
The classless way, which is the way most of us think, where the packet
goes out the most specific (i.e. with the most bits in the network)
match.
The classful way, where the router first looks at the major network (as
With this command if a route is not found in the routing table it will take
the gateway of last resort if it is set .
Without this command it will just drop the packet if a classful route is not
found in the routing table.
Jason
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL
With "no ip classless" the router looks for an exact match for a route. If
not found the packet is dropped. So if the packet destination is 172.16.33.1
and 172.16.33.0 /24 is not in the table then it goes into the bit bucket.
With "ip classless" if an exact match is not found then a less specific
IP Classless is used for route summarization and for further subnetting a
subnet for point-to-point WAN links using VLSM.It is important because by
using ip classless u can perform route summarization thereby saving on
bandwidth utilization,router processing and reduce the size of routing
tabl
By default, when performing a look-up in the route table a router will
first try to match the major network then the subnet--if there's no
match and no default network route, the packet's dropped. Again this is
the default behavior.
With ip classless, you enable the router to forward the packe
let's assume that we have network 10.0.0.0 and its subnet 10.1.0.0/16
10.2.0.0, 10.3.0.0 ... and a default route
ip route 0.0.0.0 0.0.0.0 serial 0
10.0.0.0
10.1.0.0
10.2.0.0
10.3.0.0
S 0.0.0.0 0.0.0.0 (Serial 0)
when a packet reach the router and ask for the destination 10.1.1.1
no ip classless means route IP over classful boundaries - you'll have to do
your homework to learn the Class A, Class B, and Class C network prefixes
though, mate ;-) However, 10.0.0.0 is a private (RFC 1918),
non-Internet-routeable Class A network
the route statement means that the route to n
At 12:21 AM 4/9/01, EA Louie wrote:
>no ip classless means route IP over classful boundaries - you'll have to do
>your homework to learn the Class A, Class B, and Class C network prefixes
>though, mate ;-) However, 10.0.0.0 is a private (RFC 1918),
>non-Internet-routeable Class A network
>
>the
Wrong.
ip classless allows a router receiving a packet it doesn't know how to forward
(unrecognized subnet and no default route in the routing table) to choose the
best supernet to forward it finally. Otherwise with no ip classless, the packet
is discarded.
cvp
ccnp, ccda
"Yee, Jason" <[E
Ah yes, classful addressing. Blast from the past...
I am assuming you are aware of the classes of IP addresses, and how a
class A address has a first octet of 1-127, etc..
Well, what IP Classless means is that the router *does not* assume that an
IP address with a first octet of 1-126 is a
Turns out that ip classless is enabled by default. Perhaps that is why you
need to use "no ip classless" See the www.cisco.com for details.
Ip Classless - 11.3 The default behavior changed from disabled to enabled
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
RIP and IGRP are Classful routing protocols. Meaning that they will
recognize and IP by the first octet and automatically use the default mask
associated with that class. They will disregard any subnets. Therefore you
have the ip classless command which tells these protocols to forget about
the de
ed for non-connected subnets of the same major
classful network, the packets will be dropped at the router.
- Original Message -
From: Casey Fahey <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Tuesday, August 22, 2000 8:48 PM
Subject: Re: ip class
]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, August 23, 2000 12:27 AM
Subject: Re: ip classless ?
> This is wrong amigo.
>
> The 'ip classless' command is used when configuring default routes. It is
> used because when you create a default route on a router it gets
[mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 23, 2000 3:27 AM
To: [EMAIL PROTECTED]
Subject: Re: ip classless ?
This is wrong amigo.
The 'ip classless' command is used when configuring default routes. It is
used because when you create a default route on a router it gets advertised
and AS over the interfaces configured with and
IP address in the network statement under the routing process.
David
-Original Message-
From: Adam Hickey [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, August 23, 2000 4:26 PM
To: [EMAIL PROTECTED]
Subject:Re: ip classless ?
arly distance-vector routing protocols.
Have a good one,
Casey
>From: "whatshakin" <[EMAIL PROTECTED]>
>Reply-To: "whatshakin" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Subject: Re: ip classless ?
>Date: Wed, 23 Aug 2000 00:27:27 -0700
>
Guy's,
"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."
Fenris
ng to
think at that time of the morning.
Hope you get some ZZZ's tonight!
- Original Message -
From: Casey Fahey <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, August 23, 2000 8:36 AM
Subject: Re: ip classless ?
> Wrong? Me? Golly, I had trouble
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
yes
"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 clas
-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
Let me explain the difference. The best description of
it I've seen documented is in the networkers 2000 or
1999 Intro to routing presentation I believe. I can't
locate it at the moment.
Anyway, the 'ip classless' and 'no ip classless'
global IP options modify the routers *forwarding*
decision.
, SBM, A Gates/Arrow Co.
Vox 770-623-3430 11455 Lakefield Dr.
Fax 770-623-3429 Duluth, GA 30097-1511
=
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
EA Louie
Sent: Monday, April 09, 200
in my experience with having two default routes on a router, they've
load-shared across those two interfaces/links.
For example, we had a router with a fibre connection and also a wireless
connection. The router had two default routes - one across fibre, one
across wireless. The fibre went dow
ou'll find all the defaults.
Kenny
- Original Message -
From: "Emilia Lambros" <[EMAIL PROTECTED]>
To: "'Dave Page '" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Monday, August 07, 2000 7:55 PM
Subject: RE: IP classless/Default route
I believe that is a mistake in Todd's book. You can only have one default
gateway set.
Otherwise the packet would not know where to send the packet.
Duck
- Original Message -
From: Dave Page <[EMAIL PROTECTED]>
To: 'Cisco List' <[EMAIL PROTECTED]>
Sent: Monday, August 07, 2000 5:05 PM
Subj
Dave,
If you have a CCO login check this page out. It explains the differences
between Default Gateway, Gateway of last resort, and default network. If
you don't have a CCO login, let me know and I will paraphrase the article.
Hope this helps.
http://www.cisco.com/warp/customer/105/default.
No, there is nothing incongruous here. You add the static route for the
default route which tells the router that "if you don't know where the
destination is, just shove it out over here". Lammle has to use the two
static route commands because router B is in the middle of two networks. So
when ro
t: Tuesday, August 08, 2000 8:28 AM
To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
Subject:RE: IP classless/Default routes
Dave,
If you have a CCO login check this page out. It explains the differences
between Default Gateway, Gateway of last resort, and default network. If
you don't
m: Donald B Johnson Jr [SMTP:[EMAIL PROTECTED]]
> Sent: Tuesday 08 August 2000 19:15
> To: Dave Page; 'Cisco List'
> Subject: Re: IP classless/Default routes
>
> I believe that is a mistake in Todd's book. You can only have one default
> gateway set.
> Otherw
.0.0.0 0.0.0.0 162.16.40.2
>ip route 0.0.0.0 0.0.0.0 162.16.20.1 3 3 being
> the weight
>
> > -Original Message-
> > From: Donald B Johnson Jr
> [SMTP:[EMAIL PROTECTED]]
> > Sent: Tuesday 08 August 2000 19:15
> > To: Dave Page
t by: cc:
nobody@groups Subject: RE: IP classless/Default routes
--- Original Message -
From: Donald B Johnson Jr <[EMAIL PROTECTED]>
To: Dave Page <[EMAIL PROTECTED]>; 'Cisco List' <[EMAIL PROTECTED]>
Sent: Tuesday, August 08, 2000 11:14 AM
Subject: Re: IP classless/Default routes
> I believe that is a mistake in Todd's book.
ent: Tuesday, August 08, 2000 11:28 AM
To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
Subject: RE: IP classless/Default routes
Dave,
If you have a CCO login check this page out. It explains the differences
between Default Gateway, Gateway of last resort, and default network. If
you don't have
At 08:41 PM 09/24/2000 -0500, Yee, Jason wrote:
>With this command if a route is not found in the routing table it will take
>the gateway of last resort if it is set .
>
>Without this command it will just drop the packet if a classful route is not
>found in the routing table.
>
>Jason
>
Without
Okay, I just tried this with RIP advertising the default route and I'm even
more confused! Now, it behaves as I would expect. With no ip classless,
pings to unknown 10.x.x.x subnets are unroutable even though there is a
default route in the routing table.
With no ip classless, why does my route
I guess in faovour of metric.
"John Neiberger" <[EMAIL PROTECTED]> ¼¶¼g©ó¶l¥ó
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Okay, I just tried this with RIP advertising the default route and I'm
even
> more confused! Now, it behaves as I would expect. With no ip classless,
> pings to unknown 1
Metric shouldn't have anything to do with it. Whether I'm using RIP or OSPF
the default route is being added to the routing table of the hub router.
The issue is that with no ip classless configured, the hub router should NOT
ever pick the default route when trying to reach unknown subnets of th
Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
John Neiberger
Sent: Sunday, March 25, 2001 1:32 PM
To: Vincent
Cc: [EMAIL PROTECTED]
Subject: Re: IP Classless Revisited (More info)
Metric shouldn't have anything to do with it. Whether I'm using RIP or
OSPF
Duluth, GA 30097-1511
=
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
John Neiberger
Sent: Sunday, March 25, 2001 1:32 PM
To: Vincent
Cc: [EMAIL PROTECTED]
Subject: Re: IP Classless Revisited (Mor
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
12/24/2001 5:35pm Monday
Well said
- Original Message -
From: ""Mike""
Newsgroups: groupstudy.cisco
Sent: Monday, December 24, 2001 5:35 PM
Subject: Re: IP classless command [7:30056]
> The best way to explain IP classless is to explain how a router works
IP CLASSLESS is a little hard to understand. Even Cisco is very vague on
this. Once a
TAC engineer just told me that the command just makes routing better. Here
is what I
believe happens.
If you don't have the "IP CLASSLESS" command defined in a Cisco router then
the router
will not forward a
Hello Mike. thanks so much for your detailed explanation. However, I'm
still confused about how the ip classless works. I understand that
"classful" rules (if no ip classless is configured), with the 10.1.1.0/24
static route, it would forward anything from 10.1.1.1 to 10.1.1.254, but why
would
y weird behavior and should be
configured in modern networks only very cautiously.
Dave
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Hunt Lee
Sent: Tuesday, December 25, 2001 5:45 PM
To: [EMAIL PROTECTED]
Subject: Re: IP classless command [7:30056]
He
For a simple explanation if IP classless, see:
http://www.networkking.net/out/ipclassless.htm
Bernard
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, December 25, 2001 12:41 PM
> To: [EMAIL PROTECTED]
> Subject: Re: IP class
Brilliant!
Pierre-Alex
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Bernard Omrani
Sent: Tuesday, December 25, 2001 7:21 PM
To: [EMAIL PROTECTED]
Subject: RE: IP classless command [7:30056]
For a simple explanation if IP classless, see:
http
---
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, December 25, 2001 12:41 PM
> > To: [EMAIL PROTECTED]
> > Subject: Re: IP classless command [7:30056]
> >
> > IP CLASSLESS is a little hard to understand. Even Cisco is very vague
> on
John,
Interesting. I think this is due to OSPF, not redistribution problem. Can you try
running RIP instead of OSPF ?
Cheers,
YY
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
John Neiberger
Sent: Sunday, March 25, 2001 5:28 AM
To: [EMAIL PROTECT
Sure, I'll try that but I don't see why it should matter. As I understand
it, ip classless affects routing table lookups only and it doesn't care how
those routes were installed into the table.
Although, given this behavior, my assumption might be wrong.
Thanks,
John
> John,
> Interesting.
I'm not sure how that helps in this case. In both scenarios, whether using
RIP or OSPF, the default route is being learned dynamically by the hub
router and it is installed into the routing table. The problem is that with
no ip classless configured, that router should never use the default route
ll be
defined.
Phil
- Original Message -
From: "John Neiberger" <[EMAIL PROTECTED]>
To: "YY" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Sunday, March 25, 2001 3:01 PM
Subject: RE: IP Classless Revisited (this is just odd...)
> Sure, I&#
Not that its at all helpful in this situation, but ip classless, much like bgp
synchronization, fall into the category of commands that simply defy understanding
when presented with test criteria. One must keep in mind that these are
implementations of code that sometimes are not 100% reflecti
Heh heh...yes, ip classless and bgp synchronization do fit into that
category quite well!
I am starting to think this is an IOS feature on this router. I tried this
with RIP, EIGRP, and OSPF. 'no ip classless' behaved exactly as expected
when running RIP and EIGRP. It was only when I used OS
You don't need the "ip classless" command because your default route points
to an unnumbered serial interface. If instead it pointed to an IP address
that was in the same class as your local Ethernet, then you would have a
problem. Here's the classic example:
e0 RouterA s0 -- s0 RouterB -
It will work fine for any destination other then
210.210.210.x/24 which is the classful network for
your IP subnet.
A better real-world internet example with no ip
classless and internet connections would be, if you
had a 64.x.x.x subnet on the serial and similar on LAN
side. In this case, 64.0.
Hmm,
Try removing your static 0.0.0.0 and you'll see why.
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Thursday, September 12, 2002 8:57 PM
To: [EMAIL PROTECTED]
Subject: ip classless and default route [7:53231]
according to many books, ip classless should
Akiddeledivydo
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Cthulu, CCIE Candidate
Sent: Wednesday, September 27, 2000 7:09 AM
To: [EMAIL PROTECTED]
Subject:IP Classless (from Q&A Forum at Cisco)
I got this off teh Q&A forum, and thou
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