Hi, I am just after a bit of clarification. With Classful routing protocols I have heard a lot of different information. Some people say a network cannot be subnetted, e.g the network 10.1.1.0 /24 is actually advertised as 10.0.0.0 /8 if a Classful routing protocol (such as Rip v1) is used. Others say you can subnet the network address so long as each subnet uses the same subnet mask, e.g the 10.0.0.0/8 network can be subnetted into 10.1.1.0 /24, 10.1.2.0 /24, 10.1.3.0 /24
Could someone please shed some light on this?
yes if subnet 10.1.0.0 was connected to 10.5.0.0 which was connected to 10.2.0.0 it would be classified as contiguous.
No I do not mean to say that the classful routing protocols advertise the subnet mask. The classful routing protocols assume that the same subnet mask will be used on all subnets within the same major network and therefore there is no need to advertise the subnet mask.
As to your last question, I mean that when you create the first subnet within network 10 you can choose any subnet mask that makes sense. But when you create the second subnet (and all other subnets) it is important that they all use the same subnet mask. Lets assume that you are subnetting network 10. So you create 10.1.0.0/24. Then all subnets within network 10 need to use /24 masks. When you create subnets within network 172.16 you can choose a different mask (perhaps a /22) but then all subnets of 172.16 need to use the same subnet mask.
A classful routing protocol does not support VLSM/discontiguous networks because they do not advertise the subnet mask with routing updates.
So if you had 10.1.0.0/24 on R1 and 10.2.0.0/24 on R2 and both were advertising to R3 using RIPv1, then R3 would just simply see two routes for 10.0.0.0/8, one from each of the routers.
Hope this helps.