Sample Subnetting Topology

The figure above illustrates a topology which can route the same network number over 3 segments, one of which is linked across a PPP connection. The /24 network was split into 4 subnets (since you may only produce 2^n subnets) using a /26 mask.

Configuration

Each router and workstation will use a 255.255.255.192 subnet mask in its IP configuration. The default gateway will always be the IP address of the closest router to the Internet on the segment.

TCP/IP Config

Subnet 3 - 38.9.211.128/26
The following use 38.9.211.129 as a default gateway:

38.9.211.130
28.9.211.131
38.9.211.132

Subnet 2 - 38.9.211.64/26
The following use 38.9.211.65 as a default gateway:

38.9.211.69
38.9.211.68
38.9.211.67
38.9.211.66

Subnet 1 - 38.9.211.0/26
The following use 38.9.211.1 as a default gateway:

38.9.211.5
38.9.211.4
38.9.211.3
38.9.211.2

Static vs. Dynamic Routing

Internal routing may be accomplished statically or dynamically. For dynamic routing, an internal protocol such as rip may be used. Each router will create its own routing table based on rip announcements. If static routing is preferred, the tables will need to be created manually. The table below illustrates what the routing table will look like on each router. The default gateway is identified by the 0.0.0.0 route which refers to any route that is not explicitly matched in the routing table.

Router 4 (38.9.211.129)
0.0.0.0 via PPP WAN link

Router 3 (38.9.211.69)
0.0.0.0 via 38.9.211.65
38.9.211.128 255.255.255.192 via PPP WAN link

Router 2 (38.9.211.5)
0.0.0.0 via 38.9.211.1
38.9.211.128 255.255.255.192 via 38.9.211.69
38.9.211.64 255.255.255.192 via 38.9.211.65

Router 1 (38.9.211.1)
0.0.0.0 via WAN link or PSINet POP IP address
38.9.211.128 255.255.255.192 via 38.9.211.5
38.9.211.64 255.255.255.192 via 38.9.211.5
38.9.211.0 255.255.255.0 via 38.9.211.1 (Full /24 announcement)