Lab ID: PTL-0012
Title: Configuring Cisco IOS DHCPv4 Server and Relay Agent
Status: TESTED_PASS (Verified live in Cisco Packet Tracer 9.0.1 via MCP loopback bridge automation)
1. Packet Tracer Topology Construction Manifest#
To construct or manually verify this topology in Cisco Packet Tracer:
Device Inventory#
| Device Role | PT Device Model | Display Name | Modules / Slots |
|---|---|---|---|
| Branch Gateway & Relay | Cisco ISR 4321 | R1 | Default GigabitEthernet interfaces |
| Central HQ & DHCP Server | Cisco ISR 4321 | R2 | Default GigabitEthernet interfaces |
| Branch Access Switch | Cisco Catalyst 2960-24TT | S1 | 24 FastEthernet + 2 GigabitEthernet ports |
| HQ Access Switch | Cisco Catalyst 2960-24TT | S2 | 24 FastEthernet + 2 GigabitEthernet ports |
| Branch Client Workstation | PC-PT | PC-Client-1 | FastEthernet0 |
| HQ Client Workstation | PC-PT | PC-Client-2 | FastEthernet0 |
Physical Cabling Matrix#
| Link ID | Source Device | Source Port | Destination Device | Destination Port | Cable Type |
|---|---|---|---|---|---|
| L-01 | PC-Client-1 | FastEthernet0 | S1 | GigabitEthernet0/1 | Copper Straight-Through |
| L-02 | S1 | GigabitEthernet0/2 | R1 | GigabitEthernet0/0/0 | Copper Straight-Through |
| L-03 | R1 | GigabitEthernet0/0/1 | R2 | GigabitEthernet0/0/1 | Copper Straight-Through (or Crossover) |
| L-04 | R2 | GigabitEthernet0/0/0 | S2 | GigabitEthernet0/2 | Copper Straight-Through |
| L-05 | S2 | GigabitEthernet0/1 | PC-Client-2 | FastEthernet0 | Copper Straight-Through |
2. Positive Verification Test Matrix#
| Test ID | Objective | Command / Procedure | Expected Result | Pass Criteria |
|---|---|---|---|---|
| V-01 | Verify R2 Interface and DHCP Pools | R2# show ip interface briefR2# show ip dhcp pool |
Gi0/0/0 (192.168.20.1) and Gi0/0/1 (10.0.0.2) are up/up. Both BRANCH_POOL and HQ_POOL are defined with 10 excluded addresses each. |
Pools active, interfaces up |
| V-02 | Local HQ Client DHCP Lease (PC-Client-2) | PC-Client-2 Desktop -> IP Configuration -> Click DHCP | Status reports DHCP request successful. IP: 192.168.20.11, Mask: 255.255.255.0, Gateway: 192.168.20.1, DNS: 208.67.222.222. |
Dynamic lease assigned within pool range |
| V-03 | Verify R1 Relay Agent Interface | R1# show ip interface briefR1# show running-config interface Gi0/0/0 |
Gi0/0/0 displays ip address 192.168.10.1 255.255.255.0 and ip helper-address 10.0.0.2. |
Helper address bound to client-facing interface |
| V-04 | Remote Branch Client DHCP Lease (PC-Client-1) | PC-Client-1 Desktop -> IP Configuration -> Click DHCP | Status reports DHCP request successful. IP: 192.168.10.11, Mask: 255.255.255.0, Gateway: 192.168.10.1, DNS: 208.67.222.222. |
Dynamic lease relayed across routed WAN |
| V-05 | Central Server Active Bindings | R2# show ip dhcp binding |
Contains two bindings: 192.168.10.11 mapped to PC-Client-1 MAC and 192.168.20.11 mapped to PC-Client-2 MAC. Type: Automatic. |
Both subnets present in binding database |
| V-06 | End-to-End Inter-Site Ping | PC-Client-1> ping 192.168.20.11 |
4 echo requests sent; ICMP replies received (success rate 75-100% accounting for initial ARP). | Cross-network reachability confirmed |
3. Negative & Fault Tolerance Test Matrix#
| Test ID | Fault Scenario | Injection Procedure | Observed Symptom | Recovery Procedure |
|---|---|---|---|---|
| NEG-01 | Missing DHCP Relay Helper Address | On R1:interface Gi0/0/0no ip helper-address 10.0.0.2On PC-Client-1: Release & renew DHCP. |
PC-Client-1 broadcasts DHCP Discover, but no Offer arrives. Packet Tracer outputs DHCP failed. APIPA is being used. with IP 169.254.x.x. |
On R1 Gi0/0/0, reapply ip helper-address 10.0.0.2. Renew DHCP on PC-Client-1. |
| NEG-02 | Asymmetric Return Route Failure | On R2:no ip route 192.168.10.0 255.255.255.0 10.0.0.1On PC-Client-1: Renew DHCP. |
Discover reaches R2 via unicast relay, R2 creates binding, but cannot unicast Offer back to 192.168.10.1. Client times out with APIPA. |
On R2, restore ip route 192.168.10.0 255.255.255.0 10.0.0.1. |
| NEG-03 | Gateway Address Exclusion Protection | On R2, check first lease issued in each pool. | Leased IPs start at .11 (192.168.10.11 and 192.168.20.11). Addresses .1 through .10 are skipped. |
Verified: ip dhcp excluded-address protects gateway and static reservations. |
4. Save and Persistence Verification Check#
- On R1 and R2, execute
copy running-config startup-config. - Save the topology file (
.pkt). - Close and relaunch Cisco Packet Tracer.
- Reload the saved
.pktfile. - Verify on R2:
show running-config | section dhcppreserves both pools and exclusion ranges. - Verify on R1:
show running-config interface Gi0/0/0retainsip helper-address 10.0.0.2. - Confirm PC-Client-1 and PC-Client-2 maintain or immediately renew valid dynamic leases.