Classful vs Classless Routing Protocol

walid97

Hi,

I know that RIP1 and IGRP are classful protocols.. with classful can we use subnetting like using 172.16.10.0/24, 172.16.20.0/24? or it should be only class B networks(as example)? (172.16 is class .

If we can use 172.16.10.0/24 do we type:
"Router(config-router)#Network 172.16.0.0" for both interfaces or,
172.16.10.0 and 172.16.20.0 for interface 1 and 2 respectively?

If we can use these 2 networks, can we go further and use different subnets in RIP1 and IGRP (VLSM) and let these protocols determine the subnet?

What about RIP2 (which is classless) do we type Network 172.16.0.0 or both 172.16.10.0 and 172.16.20.0 ?? (this is classB subnetted /24)



Now about static routing, we type:
"Router(config)# ip route 172.16.10.0 255.255.255.0 172.16.20.1"
in static routing, can VLSM be used, that is different subnets?? because the Mask is included in the configuration, so I don't see why VLSM cant be used here.


thanks a lot !

rossonieri#1

classful : 10.10.10.0 = 10.0.0.0
classles : 10.10.10.0 = 10.10.10.0 ( ex. only )

walid97

Well, in the Sybex book I found out that we must use for IGRP AND EIGRP:

R(config-router)#Network 172.16.0.0
for a router that has 2 subnets (172.16.16.0/20 and 172.16.32.0/20)..

dunno I am confused here !

rossonieri#1

your book saying that if you have 2 different subnet on your network :
172.16.0.0 and 172.16.1.0 then you would configure your igrp as network 172.16.0.0 that is because igrp is classful routing protocol.
but if you want to use eigrp then you would enable the ip classles command ; and enter those 2 network separately as 172.16.0.0 + 172.16.1.0.

walid97

No dude, I am sure of it.. it is EIGRP.. it in on the Sybex CCNA book, page 300.

a router has 3 interfaces with: 172.16.20.0/24, 172.16.30.0/24 and 172.16.40.0/24.

the configuration is:
R(config)# router eigrp 100
R(config-router)# network 172.16.0.0

so eventhough EIGRP is classless, it used a classfull notation.
is this a mistake !

Drakonblayde

two words: route summarization

walid97

This means that we use the "172.16.0.0" network for both.. No need to type each subnet..

forbesl

EIGRP summarizes by default. If you don't want it to summarize, you have to input "no auto-summary" into your EIGRP statement.

Example:
router eigrp 2000
network 172.16.0.0
network 10.0.0.0
no auto-summary

This way the router will not summarize any networks in its EIGRP table, but will see all of the components of each network:

one#show ip eigrp topology
IP-EIGRP Topology Table for process 2000

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - Reply status

P 10.1.3.0/24, 1 successors, FD is 46354176
via 20.1.1.1 (46354176/45842176), Serial0
P 10.1.2.0/24, 1 successors, FD is 11049472
via 20.1.1.1 (11049472/10537472), Serial0
P 10.1.1.0/24, 1 successors, FD is 11023872
via 20.1.1.1 (11023872/10511872), Serial0
P 172.16.1.0/24, 1 successors, FD is 2169856
via Connected, Serial0

Without turning off auto summarization, EIGRP would have summarized these networks to 10.0.0.0/8 and 172.16.0.0/16