Classless vs Classful in regards to RIP

Would you guys agree with these definitions?

Classful routing protocols do not send subnet mask information with their
routing updates.

Classless routing protocols do send the subnet mask with their updates.

Taken from:
http://www.routeralley.com/ra/docs/classless_classful.pdf

I ask not to nitpick, but when a word usually contains -less that means it's missing something. In this usage though, the classless *includes* the subnetmask? Does it seem like these are turned around to anyone else?

I'm basiclly trying to make sure I understand the difference between RIP and RIPv2.

Also am I correct in the assumption that the only difference in the configuration is that you just add the line;

version 2

When using RIPv2?

example RIP
R1(config)#router rip
R1(config-router)#network 10.0.0.0
R1(config-router)#network 192.168.1.0

RIP v2
R1(config)#router rip
R1(config-router)#version 2
R1(config-router)#network 10.0.0.0
R1(config-router)#network 192.168.1.0

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Comments

trackit

ipv4 aadresses were originally developed as 3 major classes:

A 0XXXXXXX 0 - 127 (mask 255.0.0.0)
B 10XXXXXX 128 - 191 (mask 255.255.0.0)
C 110XXXXX 192 - 223 (mask 255.255.255.0)

if you assume that all ip addresses use their default classful netmasks then you dont even need to specify netmask cause you can just determine to what class ip address belongs and take that classful netmask.

if you assume that ip addresses do not need to have their default classful netmask and they can be subnetted then you do have to specify subnetmask. This is referred as classless cause you dont use default classful masks.

Neeko

RIPv2 and other classless routing protocols are classless because they function without the restrictions of traditional network classes. Classful protocols such as RIPv1 are classful because they do function according to network classes.

You may need to do some more reading on IP addressing in order to understand where the terms classful and classless stem from. The terms themselves do not directly match whether or not the subnet mask is sent, and to think so makes me think you don't understand what the terms actually mean.

You are right in saying classful routing protocols do not send the subnet mask and classless protocols do, but whats important to understand is why this is the case.

billscott92787

Read up on the difference between the two. Classful doesn't support VLSM and classless does. This means that you can only subnet based on the classful address. For example

A /8

B /16

C /24

In addition, it isn't necessarily the "act" of the classful or classless addressing that sends the routing updates. It is the routing protocol. RIPv1 is a classful routing protocol. RIPv2 is a classless. RIPv1 does not send subnet masks in it's routing updates. RIPv2 does. Just read up on the difference between classful and classless addressing.

pwjohnston

Neeko wrote: »

The terms themselves do not directly match whether or not the subnet mask is sent, and to think so makes me think you don't understand what the terms actually mean.

Well, that is what I was looking for. So no, that is not a good definition. That link I posted is not mine. While trying to understand why RIP and RIPv2 are different, I found it while searching for just a plain clear definition of classless protocol and classful protocol.

Thanks for the replies.

bigheadx

As others has said,

RIPv2 was created in addition to VLSM and CIDR because of the shortage of addresses.

ISP were handing out blocks at a time, and alot of spaces were going to waste.

For ex, why give a company 10.0.0.0 /8, with a crap ton of hosts, when you can give them 69.68.3.25 /29 , giving them 14 usables?

VLSM was tricky at first, but you should able to get it.

Wait until you get into EIGRP and OSPF. "Here ye, Here ye, The has taken the throne"

HAHA!

Neeko

pwjohnston wrote: »

Well, that is what I was looking for. So no, that is not a good definition. That link I posted is not mine. While trying to understand why RIP and RIPv2 are different, I found it while searching for just a plain clear definition of classless protocol and classful protocol.

Thanks for the replies.

The way it works is as you've said it. The terms aren't meant to literally indicate (by the pure meaning of the word used) whether the subnet mask is sent. As it is though, the terms do indirectly indicate whether the mask is sent, because after all whichever type of protocol is used will have many implications including the inclusion of masks in routing updates.

The terms themselves simply describe whether or not IP address classes are abided by and this is what dictates whether or not masks are included, whether VLSM is supported etc.

If you study IP addressing, subnetting, RIPv1 and RIPv2 then all should be clear

EdTheLad

The definitions in the initial post are correct!
Most of the following explanations of classful routing are not.Classful routing does not mean you cannot subnet, it means you cant vary the subnet of a major network address.So if you use 11.0.0.5/28 in your classful network everytime you use an address with the classful address 11.x.x.x you must keep the same /28 mask.Classless which supports VLSM allows you to vary the mask so yu coud have 11.x.x.x/28 11.x.x.x/30 etc in the same classful domain.
Just to drive it home in a classful network you could have networks:
10.1.1.1/30
10.2.2.1/30
10.150.120.1/30
150.11.3.2/24
150.11.4.1/24

You cannot vary the major network as follows:
10.1.1.1/30
10.2.2.1/30
10.150.120.1/24
150.11.3.2/24
150.11.4.1/28

How classful RIP works is it assumes that an update arriving with the same major network as the arriving interface will share the subnet that is configured on the interface.
So if the interface has an ip address 10.0.0.1/24, an update arrives without a mask 10.1.1.0, Rip will see that the 10.x.x.x matches the interface and so it must share the masks of the interface i.e. /24.So 10.1.1.0/24 is put i the RIB.
If another update arrives on the same interface with an ip address 140.1.1.1(without a mask) RIP does not know what mask to assign so it defaults to the classful mask, 140 is a class B so 140.1.0.0/16 will be entered into the RIB.

Neeko

EdTheLad wrote: »

The definitions in the initial post are correct!
Most of the following explanations of classful routing are not.Classful routing does not mean you cannot subnet, it means you cant vary the subnet of a major network address.So if you use 11.0.0.5/28 in your classful network everytime you use an address with the classful address 11.x.x.x you must keep the same /28 mask.Classless which supports VLSM allows you to vary the mask so yu coud have 11.x.x.x/28 11.x.x.x/30 etc in the same classful domain.
Just to drive it home in a classful network you could have networks:
10.1.1.1/30
10.2.2.1/30
10.150.120.1/30
150.11.3.2/24
150.11.4.1/24

You cannot vary the major network as follows:
10.1.1.1/30
10.2.2.1/30
10.150.120.1/24
150.11.3.2/24
150.11.4.1/28

How classful RIP works is it assumes that an update arriving with the same major network as the arriving interface will share the subnet that is configured on the interface.
So if the interface has an ip address 10.0.0.1/24, an update arrives without a mask 10.1.1.0, Rip will see that the 10.x.x.x matches the interface and so it must share the masks of the interface i.e. /24.So 10.1.1.0/24 is put i the RIB.
If another update arrives on the same interface with an ip address 140.1.1.1(without a mask) RIP does not know what mask to assign so it defaults to the classful mask, 140 is a class B so 140.1.0.0/16 will be entered into the RIB.

Of course, this is all true, but since he's somewhat unsure about the very basics I didn't want to start talking about fixed length masks within major networks, crossing boundaries, auto summarization etc because I thought it would complicate things too much at this stage. At the same time though, its difficult to to tell half a story and I think thats what the rest of us were doing.

I suspect your post, albeit informative and correct will give him a wtf moment

Mark Knutson

pwjohnston wrote: »

Would you guys agree with these definitions?

Classful routing protocols do not send subnet mask information with their
routing updates.

Classless routing protocols do send the subnet mask with their updates.

That is my understanding as well. A classful protocol infers the subnet mask from the traditional class implied in the first octet.

aaronbalchunas

pwjohnston wrote: »

Would you guys agree with these definitions?

Classful routing protocols do not send subnet mask information with their
routing updates.

Classless routing protocols do send the subnet mask with their updates.

Taken from:
http://www.routeralley.com/ra/docs/classless_classful.pdf

I ask not to nitpick, but when a word usually contains -less that means it's missing something. In this usage though, the classless *includes* the subnetmask? Does it seem like these are turned around to anyone else?

I am the author of the guide in the above link, and I want to clarify a couple of things. Yes, the most basic difference between classful and classless routing protocols is whether or not the subnet mask is included with updates, as you quoted me.

However, to boil the entire discussion down to just that doesn't work. Which is why that guide is several pages long, and not simply two sentences.

The repercussions of sending/not sending the subnet mask are the meat of the discussion, and how classful and classless protocols react in various situations.

As many other people in this thread stated, understanding the complexities of classful/classless routing will be difficult without a complete grasp of how IP addressing works (note that I keep bolding routing - though related, classful/classless routing and classful/classless IP addressing are two very different discussions).

There's a plethora of great information about IP out on the Internet, and I have a pretty exhaustive guide on IP addressing/subnetting on my website as well.

Fortunately, this discussion is mostly academic these days anyway - I don't run into too many companies still running classful routing (thankfully).

Take care,

- Aaron Balchunas
http://www.routeralley.com