Classless & Classful Routing

DerekAustin26

Whats the difference?

Classless just use "IP Subnet Zero"

and Classful doesnt?

Am I understanding this correctly?

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Comments

Xenz

You're talking about classless and classful routing protocols? Classful (RIP/IGRP) do not send subnet masks, classless (RIPv2/EIGRP/OSPF) send subnet masks in their updates. ip subnet zero has nothing to do with this.

nutech444

Classless routing protocols are the protocols supporting Classless Inter-Domain Routing (CIDR), a newer scheme of IPv4 addressing. The mostly used Classless routing protocols include RIP v2 v3 and v4, EIGRP, OSPF, IS-IS and BGP4.

If a network address is subnetted, the first subnet obtained after subnetting the network address is called subnet zero.

Subnet Zero and the All-Ones Subnet [IP Addressing Services] - Cisco Systems

both are very imp concepts if you are working towards the ccna/ccent, cisco will most def test you on that, you have know this cold along with rest of the book ; )

Xenz

nutech444 wrote: »

Classless routing protocols are the protocols supporting Classless Inter-Domain Routing (CIDR), a newer scheme of IPv4 addressing. The mostly used classful routing protocols include RIP v2 v3 and v4, EIGRP, OSPF, IS-IS and BGP4.

If a network address is subnetted, the first subnet obtained after subnetting the network address is called subnet zero.

Subnet Zero and the All-Ones Subnet [IP Addressing Services] - Cisco Systems

both are very imp concepts if you are working towards the ccna/ccent, cisco will most def test you on that, you have know this cold along with rest of the book ; )

The protocols you listed are not classful unless you meant classless. Your definition of CIDR seems slightly off.

nutech444

yes its classless that was a typo thanks for pointing that out.

Here is a great guide on IP addressing

http://www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf

DerekAustin26

Xenz wrote: »

You're talking about classless and classful routing protocols? Classful (RIP/IGRP) do not send subnet masks, classless (RIPv2/EIGRP/OSPF) send subnet masks in their updates. ip subnet zero has nothing to do with this.

So whats the difference between RIP/IGRP & RIPv2/EIGRP/OSPF ? RIP/IGRP uses distance vector while the latter uses Link-state?

bubble2005

DerekAustin26 wrote: »

So whats the difference between RIP/IGRP & RIPv2/EIGRP/OSPF ? RIP/IGRP uses distance vector while the latter uses Link-state?

RIP and IGRP are classful routing protocols that do not send subnet mask information with their routes. They are both distance vector protocols. RIPv2 is also a distance vector protocol however it is a classless distance vector protocol meaning that it sends subnet mask information with it's routes. Such subnet mask flexibility enables you to group several networks as a single entry in a routing table, significantly reducing routing overhead. OSPF is a link state classless routing protocol and EIGRP is a hybrid protocol, a mixture of link state and distance vector, however it is also classless routing protocol.

Mark Knutson

I just read a cidr rfc document and its been around for more than 12 years. I am wondering why we are learning classful stuff since its obsolete for the most part. I suppose its just considered simpler than going full cidr.

It helped me to put it in perspective reading about how cidr helps reduce the size of routing tables through summarization when the address structure corresponds to the physical topology of the internet.

wbosher

nutech444 wrote: »

you have know this cold

You're not Chris Bryant in disguise, are you??

Xenz

Mark Knutson wrote: »

I just read a cidr rfc document and its been around for more than 12 years. I am wondering why we are learning classful stuff since its obsolete for the most part. I suppose its just considered simpler than going full cidr.

It helped me to put it in perspective reading about how cidr helps reduce the size of routing tables through summarization when the address structure corresponds to the physical topology of the internet.

No reason not to know the history of the Internet. RIP can still be used, IGRP I believe has been removed from IOS altogether. How do you make sense of CIDR/VLSM if you don't understand the need for it? There is also auto summary.