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Lab 8.2

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willtorresortiz edited this page Oct 19, 2026 · 1 revision

Lab 8.2 - Static Routing Part II

lab was done in Packet Tracer

Objective: configure two routers and multiple subnets using static routes

Part 1

Subnetting scheme

The business has 2 sites (West and East) and was assigned 154.103.16.0/21. It needs to be split into 4 user networks plus a link between the routers.

Size each subnet

Pick the smallest block with enough usable hosts (2^n - 2, where n = host bits)

Name Users Host bits Usable hosts Prefix
SalesWest 300 9 510 /23
FinanceWest 200 8 254 /24
SalesEast 100 7 126 /25
FinanceEast 50 6 62 /26
EAST-WEST link 2 routers 2 2 /30
  • assign the biggest block first so the blocks line up on their boundaries
  • the EAST-WEST link is its own network (192.168.0.0/30), it does not use any of the /21

Completed table

Name Network Address Subnet Mask Lowest Usable IP Highest Usable IP IP for Default Router
SalesWest 154.103.16.0/23 255.255.254.0 154.103.16.1 154.103.17.254 154.103.16.1
FinanceWest 154.103.18.0/24 255.255.255.0 154.103.18.1 154.103.18.254 154.103.18.1
SalesEast 154.103.19.0/25 255.255.255.128 154.103.19.1 154.103.19.126 154.103.19.1
FinanceEast 154.103.19.128/26 255.255.255.192 154.103.19.129 154.103.19.190 154.103.19.129
EAST-WEST 192.168.0.0/30 255.255.255.252 192.168.0.1 192.168.0.2 N/A
  • default router = the lowest usable IP in each network (the router interface on that LAN)
  • broadcast address is the last address in each block (ex: 154.103.17.255 for SalesWest)

Part 2

Build the network

  • Built the network from the starter file with 2960 switches
    • West Router -> Switch0 (SalesWest1, SalesWest2) and Switch1 (FinanceWest)
    • East Router -> Switch2 (SalesEast) and Switch3 (FinanceEast)
    • West Router <-> East Router link
  • Configured the router interfaces and PC addresses from the table above, no routes yet
  • Router interface addresses
    • West Router Fa0/0: 154.103.16.1/23 (SalesWest gateway)
    • East Router Fa0/0: 154.103.19.1/25 (SalesEast gateway)
    • EAST-WEST link: West side 192.168.0.1, East side 192.168.0.2

What happens when SalesWest1 pings SalesEast (before routes)?

  1. SalesWest1 compares SalesEast's IP to its own using its subnet mask - different network
  2. so it sends the ping to its default gateway (West Router, 154.103.16.1)
  3. the West Router checks its routing table - it only knows its directly connected networks, no route to SalesEast's network
  4. the West Router drops the packet

Part 3

Create static routes

Syntax: ip route <destination-network> <subnet-mask> <next-hop-ip>

  • each router only needs routes to the networks on the other side
  • next hop = the other router's address on the EAST-WEST link

West Router

WestRouter(config)#ip route 154.103.19.0 255.255.255.128 192.168.0.2
WestRouter(config)#ip route 154.103.19.128 255.255.255.192 192.168.0.2
  • routes to SalesEast and FinanceEast, through the East Router (192.168.0.2)

East Router

EastRouter(config)#ip route 154.103.16.0 255.255.254.0 192.168.0.1
EastRouter(config)#ip route 154.103.18.0 255.255.255.0 192.168.0.1
  • routes to SalesWest and FinanceWest, through the West Router (192.168.0.1)

Part 4

Test connectivity

SalesWest1 -> SalesEast

  • ping 154.103.19.2
  • 3 of 4 replies

FinanceEast -> FinanceWest

  • ping 154.103.18.2
  • 3 of 4 replies

Notes:

  • first request timed out both times - the first packet is used up resolving addresses (ARP), the rest go through
  • TTL 126 on both = 2 routers crossed (West and East), Windows starts at 128

Part 5

Show an IP address on an interface for each router

  • show ip interface on each router
WestRouter#show ip interface
EastRouter#show ip interface

Questions to consider

Q: What happens when SalesWest1 tries to ping SalesEast before routes are added?
A: SalesWest1 uses its subnet mask to determine that SalesEast is on a different network and sends the ping to its default gateway, but the West Router drops it because no route to SalesEast's network has been configured.

Q: What commands were entered on the routers to enable connectivity?
A: West Router: ip route 154.103.19.0 255.255.255.128 192.168.0.2 and ip route 154.103.19.128 255.255.255.192 192.168.0.2. East Router: ip route 154.103.16.0 255.255.254.0 192.168.0.1 and ip route 154.103.18.0 255.255.255.0 192.168.0.1

Q: How do I pick the subnet size for a number of users?
A: Find the smallest number of host bits where 2^n - 2 is at least the number of users, then the prefix is 32 minus n. (300 users -> 9 bits -> /23)

Quick Reference: Subnetting + Static Routes

  • usable hosts = 2^(host bits) - 2 (minus network address and broadcast)
  • lowest usable IP = network address + 1
  • highest usable IP = broadcast address - 1
  • assign the largest subnets first
  • a point-to-point router link only needs a /30 (2 usable hosts)
  • every router needs a route to every network it is not directly connected to
Router>enable
Router#configure terminal
Router(config)#ip route <network> <mask> <next-hop-ip>
Router(config)#exit
Router#show ip route
Router#show ip interface
Router#copy run start

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