IP Services // Lesson 01

Network Address Translation.

Configure and verify inside source NAT with static mappings, dynamic pools and port address translation.

Inside localInside globalStatic NATDynamic NATPAT
01 // Mental model

Start with the big picture.

The address assigned to an inside host before translation.

CCNA focus: Follow a packet's direction, identify inside and outside interfaces, decide which address is local versus global, then verify both the translation table and counters.
02 // Building blocks

Know what each part does.

01

Inside local

The address assigned to an inside host before translation.

02

Inside global

The globally meaningful address representing that inside host after translation.

03

Static NAT

A fixed one-to-one mapping useful when an inside service must be consistently reachable.

04

Dynamic NAT and PAT

A pool assigns temporary global addresses; overload distinguishes sessions with transport-layer ports.

03 // Compare and recognise

Read the clues.

ItemWhat to remember
ip nat insideMarks the interface facing the private/inside network.
ip nat outsideMarks the interface facing the public/outside network.
Static translationPredictable one-to-one mapping that persists.
Pool exhaustionDynamic NAT without overload fails when no global address remains available.
04 // Configure and verify

Configure and verify.

R1(config)# interface gigabitEthernet 0/0
R1(config-if)# ip nat inside
R1(config)# interface gigabitEthernet 0/1
R1(config-if)# ip nat outside
R1(config)# ip nat inside source static 10.10.10.10 203.0.113.10
R1(config)# ip nat pool PUBLIC 203.0.113.20 203.0.113.29 netmask 255.255.255.0
R1(config)# access-list 1 permit 10.10.10.0 0.0.0.255
R1(config)# ip nat inside source list 1 pool PUBLIC
R1# show ip nat translations
R1# show ip nat statistics

Read the example from top to bottom, then verify the resulting state. Configuration is only complete when the output matches the intended design.

05 // Exam and troubleshooting

Turn facts into a method.

  • Marks the interface facing the private/inside network.
  • Marks the interface facing the public/outside network.
  • Predictable one-to-one mapping that persists.
  • Dynamic NAT without overload fails when no global address remains available.
Exam checkpoint: Follow a packet's direction, identify inside and outside interfaces, decide which address is local versus global, then verify both the translation table and counters.
06 // Check yourself

Network Address Translation quiz.

1. What is an inside local address?

2. Which NAT type creates a fixed one-to-one mapping?

3. What does PAT add so many sessions can share one global address?

4. Which command displays active translations?

5. What happens when a dynamic NAT pool is exhausted without overload?

Score: 0 / 5