4.2 9 Lab Configure Ip Addresses

You're staring at a router prompt. The cursor blinks. Somewhere in the back of your mind, you know exactly what needs to happen — assign an IP, bring up the interface, verify connectivity. But the syntax? Here's the thing — the order? The exact command to make it stick without a reload?

Yeah. That's where most people hesitate That's the part that actually makes a difference..

Lab 4.Which means type the address in the wrong format. It's one of those foundational exercises that shows up early in every Cisco networking course, and it's also the one where bad habits form fast. Skip a no shutdown. Even so, 9 — Configure IP Addresses — looks deceptively simple on paper. 2.Forget the subnet mask. Suddenly you're troubleshooting a problem that shouldn't exist.

Let's walk through it properly. Not just the commands — the why behind them, the traps, and the small details that separate a working config from a Friday-night headache.

What This Lab Actually Covers

At its core, 4.2.That's why 9 is about assigning IPv4 addresses to router interfaces and verifying they work. That's it Simple, but easy to overlook..

• Configuring IP addresses on multiple interfaces (GigabitEthernet, Serial, Loopback)
• Setting subnet masks correctly — both dotted-decimal and CIDR
• Enabling interfaces with no shutdown
• Verifying with show ip interface brief, ping, and show running-config
• Sometimes: configuring a default gateway on a switch or PC simulator

It's not routing yet. No OSPF, no static routes, no ACLs. Just layer 3 addressing — the plumbing everything else sits on top of Worth keeping that in mind..

The Topology You're Probably Looking At

Most versions of this lab use a two-router, one-switch setup. Something like:

• R1: G0/0 → LAN (192.168.1.0/24), S0/0/0 → WAN link (10.1.1.0/30)
• R2: G0/0 → LAN (192.168.2.0/24), S0/0/1 → WAN link (10.1.1.0/30)
• Switch: management VLAN (192.168.1.2/24), default gateway 192.168.1.1
• PC1: 192.168.1.10/24, gateway 192.168.1.1
• PC2: 192.168.2.10/24, gateway 192.168.2.1

Your job: make every device reachable from its directly connected neighbor.

Why This Lab Matters More Than It Looks

You might think, "It's just IP addresses. I'll learn the real stuff later."

Here's the thing — this is the real stuff.

Every routing protocol, every VPN, every firewall rule, every QoS policy — they all assume the interfaces have valid, reachable IP addresses. If you can't do this cleanly, you'll waste hours later debugging OSPF adjacencies that never form because one side has a /25 and the other has a /24. Or a serial link that's up/down because someone forgot clock rate on the DCE side. Or a switch that can't be managed remotely because the default gateway points to nowhere Worth keeping that in mind..

This lab teaches discipline. Also, precision. The habit of verifying before you move on.

And honestly? In practice, it's the only lab where you get to type ip address 192. 1.255.And 255. Here's the thing — 1 255. 168.0 and feel like a network engineer for the first time. Don't rush past that Surprisingly effective..

How to Configure IP Addresses — Step by Step

Let's do this the way you'll actually do it in Packet Tracer, CML, or on real gear. Same commands. Same logic And that's really what it comes down to..

1. Enter Global Configuration Mode

Router> enable
Router# configure terminal
Router(config)#

You know this. But notice: no configure memory, no configure network. Consider this: just configure terminal. Every time Not complicated — just consistent..

2. Select the Interface

Router(config)# interface gigabitethernet 0/0
Router(config-if)#

Tab-complete works. int g0/0 works. Which means interface g0/0 works. Even so, pick a style and stick with it. Consistency saves keystrokes when you're tired.

3. Assign the IP Address and Subnet Mask

Router(config-if)# ip address 192.168.1.1 255.255.255.0

Two arguments. Mask second. No slash notation here — that's for routing tables and humans. Think about it: iP first. Space between. IOS wants dotted decimal Still holds up..

Pro tip: Say it out loud as you type. "One ninety-two, one sixty-eight, one, one — two fifty-five, two fifty-five, two fifty-five, zero." Your fingers follow your voice. Fewer typos Not complicated — just consistent..

4. Bring the Interface Up

Router(config-if)# no shutdown

This is the one everyone forgets. In practice, *Every time. * A Cisco interface is administratively down by default. no shutdown moves it to up/down (if no cable) or up/up (if connected and layer 2 is happy).

You'll see a console message:

%LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to up
%LINEPROTO-5-UPDATED: Line protocol on Interface GigabitEthernet0/0, changed state to up

That's dopamine. Enjoy it.

5. Repeat for Every Interface

Serial side? Same steps. But add clock rate on the DCE end:

Router(config)# interface serial 0/0/0
Router(config-if)# ip address 10.1.1.1 255.255.255.252
Router(config-if)# clock rate 64000
Router(config-if)# no shutdown

The clock rate command only matters on the DCE side of a serial link. In Packet Tracer, the cable tells you which end is DCE (look for the little clock icon). On real gear, show controllers serial 0/0/0 reveals it.

Loopback interfaces? Even simpler — they're always up:

Router(config)# interface loopback 0
Router(config-if)# ip address 1.1.1.1 255.255.255.255

No no shutdown needed. Loopbacks never go down unless you shut them Which is the point..

6. Configure the Switch (If Required)

Switch> enable
Switch# configure terminal
Switch(config)# interface vlan 1
Switch(config-if)# ip address 192.168.1.2 255.255.255.0
Switch(config-if)# no shutdown
Switch(config-if)# exit
Switch(config)# ip default-gateway 192.168.1.1

Two things here:

• The switch needs an SVI (VLAN interface) for management
• The ip default-gateway is not a routing command — it's only for the switch's own traffic when it's not routing

7. Verify Everything

Don't just assume it worked. Verify That alone is useful..

Router# show ip interface brief

Look for:

• Interface name
• IP address (correct?)
• Status: up
• Protocol: up

If you see administratively down → you forgot no shutdown.
If you see down/down → cable issue

8. Test Connectivity

Ping something. Anything.

Router# ping 192.168.1.2

If it works, you're done with that segment. If not, retrace your steps. Nine times out of ten, it's either a missing no shutdown or a wrong subnet mask Simple, but easy to overlook..

Don't trust the lights. Trust the ping.

9. Save Your Work

Router# copy running-config startup-config

Or the lazy way:

Router# write memory

Both do the same thing. In practice, the first is more explicit. Now, the second saves keystrokes. Pick one and use it every time. Muscle memory doesn't care which Took long enough..

10. Document What You Did

Not for the exam. For future you.

Write down:

• Interface names
• IP addresses and masks
• Which end is DCE
• Cable types used

Future you will thank present you. Especially at 2 AM during a lab exam Small thing, real impact..

Conclusion

Interface configuration follows a predictable rhythm: enter interface, assign IP, bring it up, verify. Plus, the commands don't change between router models or IOS versions. What changes is your speed and accuracy Which is the point..

Practice this sequence until it's automatic. Because of that, you should be able to configure three interfaces in under two minutes without looking at a reference. Speed comes from repetition, not memorization.

When troubleshooting, always check the basics first: no shutdown, correct IP/mask, and physical connectivity. Complex problems are rare. Simple mistakes are common.

The CLI rewards precision and punishes shortcuts. Type carefully, verify constantly, and save early. Your future self will be the one debugging at midnight, and they'll either curse or thank you depending on what you do now Which is the point..

11. Put It All Together – A Mini‑Lab Walkthrough

To cement the workflow, let’s walk through a compact scenario that stitches together everything we’ve covered so far. Imagine a three‑router topology where each router must exchange traffic with the others over distinct subnets.

1. Plan the address space

   • Router A ↔ Router B: 10.0.0.0/30 (uses IPs 10.0.0.1 and 10.0.0.2)
   • Router A ↔ Router C: 10.0.0.4/30 (uses IPs 10.0.0.5 and 10.0.0.6)
   • Router B ↔ Router C: 10.0.0.8/30 (uses IPs 10.0.0.9 and 10.0.0.10)

2. Configure the physical links

   • On each end of the serial cable, set the DCE side with clock rate 64000 and the line protocol with no shutdown.
   • Assign the chosen IPs on the respective interfaces (Serial0/0/0, Serial0/0/1, etc.).

3. Enable routing

   • Instead of static routes, enable RIP version 2 on each router:

     Router(config)# router rip
     Router(config-router)# version 2
     Router(config-router)# network 10.0.0.0
     

   • Verify neighbor relationships with show ip rip neighbor.

4. Test end‑to‑end reachability

   • From Router A, ping the loopback on Router C (ping 10.0.0.9).
   • If the ping fails, inspect the routing table (show ip route) to see whether the learned routes are present.

5. Apply a simple ACL to control traffic

   • Suppose Router B should only accept packets from the 10.0.0.8/30 subnet:

     Router(config)# access-list 10 permit ip 10.0.0.8 0.0.0.3 any
     Router(config)# interface serial0/0/1
     Router(config-if)# ip access-group 10 in
     

   • Verify the ACL’s effect with show ip access-lists.

6. Save and document

   • write memory on every device.
   • In a lab notebook, note the interface labels, IP pairs, DCE/DTE assignments, and the ACL numbers used.

By walking through a concrete example, you’ll see how each command fits into a larger picture without having to reinvent the wheel each time.

12. Going Beyond the Basics

a. Using Sub‑Interfaces for VLAN Tagging

When a single physical link must carry traffic for multiple virtual LANs, sub‑interfaces become indispensable. Configure them like this:

Router(config)# interface GigabitEthernet0/0.10
Router(config-subif)# encapsulation dot1q 10
Router(config-subif)# ip address 192.168.10.1 255.255.255.0
Router(config-subif)# exit
Router(config)# interface GigabitEthernet0/0.20
Router(config-subif)# encapsulation dot1q 20
Router(config-subif)# ip address 192.168.20.1 255.255.255.