VLSM on 4 routers

[hamtower]

I am very new to all of this and I'd like to understand it much better.

My network looks like the picture above. This is not for homework however it's just exercises to practice on but I like to learn them.

My next instructions are as follows:

The LAN with Server0 should use 10.1.1.0/24 with Router0 being the default gateway and using

10.1.1.1 as its internal, LAN facing IP. You may add any IP address to Server0 within that range.

The LAN with Server1 should use 10.1.2.0/24 with Router1 being the default gateway and using

10.1.2.1 as its internal, LAN facing IP. You may add any IP address to Server1 within that range.

The LAN with PC0 should use 10.1.3.0/25 with Router2 being the default gateway and using

10.1.3.1 as its internal, LAN facing IP. You may add any IP address to PC0 within that range.

The LAN with Laptop0 should use 10.1.3.128/25 with Router3 being the default gateway and using

10.1.3.129 as its internal, LAN facing IP. You may add any IP address to Laptop0 within that range.

I have all of these set, the IP Addresses and Subnet Masks for GigabitEthernet0/0 show correct, however I am not sure what to set the Se0/3/0 and Se0/3/1 subnet masks as, I have tried 255.255.255.0 but that did not work. 

Plus I need to VLSM route each one of these and everything I've looked at (articles and youtube videos) I just quite don't understand it.

Any help is appreciated.

[Georg Pauwen]

Hello,

VLSM just means you assign any other subnet mask than the default, called classfull, mask. The defaults are:

10.0.0.0/8

172.16.0.0/16

192.168.0.0/24

I cannot see from your picture where the serial interfaces are. Can you post the Packet Tracer project file (zip it first otherwise the system won't let you upload it) ?

[Richard Burts]

The drawing seems to indicate that all connections between routers are serial links. Is that correct? Since the original poster description does not mention any guidance for addressing or subnetting for the serial links does that indicate that he is free to use any addressing and subnetting that he might want?

My understanding of VLSM is a bit different from Georg. Subnetting is just about taking some major network (class A or class B or class C) and breaking it into smaller (and more usable size) parts. Subnetting can be standard or can be VLSM. With standard subnetting you can choose any subnet size/subnet mask you want, and all subnets must be the same size. So using a /24 mask for class A network 10.0.0.0 is not necessarily VLSM. It could be standard subnetting. A restriction in standard subnetting is that once you have chosen a mask for a subnet within a network then all other subnets in that network must use the same size mask. Using VLSM means that subnets within the same major network can use different size subnet masks.  So using 10.1.1.0/24 and 10.1.2.0/24 could be standard subnetting. But using 10.1.3.0/25 introduces a subnet within the major class A network with a different mask and this makes it VLSM.

So if the original poster has configured the LAN interfaces using a mixture of /24 and /25 then the VLSM part of the exercise has been done. Then comes the routing part. Can the original poster provide any clarification about whether routing should be with static routes or with a dynamic routing protocol?

HTH

Rick