This verification guide provides systematic testing procedures for validating DHCP relay agent operations, subinterface IP helper addresses, central DHCP server scope allocation, and end-to-end client connectivity across multiple 802.1Q VLANs.
1. Positive Verification (Completed State)#
Test POS-01: PC-VLAN10 Dynamic Lease Acquisition#
From PC-VLAN10 Desktop Command Prompt, run ipconfig /all:
ipconfig /all
Expected Output:
FastEthernet0 Connection:(default port)
Connection-specific DNS Suffix..: enterprise.local
Physical Address................: 0001.42A3.B810
Link-local IPv6 Address.........: FE80::...
IPv4 Address....................: 192.168.10.11
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.10.1
DHCP Server.....................: 10.0.0.1
DNS Servers.....................: 10.0.0.1
Criteria: Dynamic IP assigned in 192.168.10.0/24, default gateway set to 192.168.10.1, DNS set to 10.0.0.1.
Test POS-02: PC-VLAN20 Dynamic Lease Acquisition#
From PC-VLAN20 Desktop Command Prompt, run ipconfig /all:
ipconfig /all
Expected Output:
FastEthernet0 Connection:(default port)
Connection-specific DNS Suffix..: enterprise.local
Physical Address................: 00D0.FF41.562A
Link-local IPv6 Address.........: FE80::...
IPv4 Address....................: 192.168.20.11
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.20.1
DHCP Server.....................: 10.0.0.1
DNS Servers.....................: 10.0.0.1
Criteria: Dynamic IP assigned in 192.168.20.0/24, default gateway set to 192.168.20.1, DNS set to 10.0.0.1.
Test POS-03: Central DHCP Server Binding Table#
On R1-HQ, verify the active DHCP bindings:
R1-HQ# show ip dhcp binding
Bindings from all pools :
IP address Client-ID/ Lease expiration Type
Hardware address/
User name
192.168.10.11 0001.42A3.B810 -- Automatic
192.168.20.11 00D0.FF41.562A -- Automatic
Criteria: Active lease entries present for both 192.168.10.0/24 and 192.168.20.0/24 pools.
Test POS-04: PC-VLAN10 Subinterface Gateway Reachability#
From PC-VLAN10 Command Prompt, ping the local subinterface gateway:
ping 192.168.10.1
Expected Output:
Ping statistics for 192.168.10.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Test POS-05: PC-VLAN20 Subinterface Gateway Reachability#
From PC-VLAN20 Command Prompt, ping the local subinterface gateway:
ping 192.168.20.1
Expected Output:
Ping statistics for 192.168.20.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Test POS-06: Inter-VLAN Routing Reachability#
From PC-VLAN10 Command Prompt, ping PC-VLAN20:
ping 192.168.20.11
Expected Output:
Pinging 192.168.20.11 with 32 bytes of data:
Reply from 192.168.20.11: bytes=32 time<1ms TTL=127
Reply from 192.168.20.11: bytes=32 time<1ms TTL=127
Reply from 192.168.20.11: bytes=32 time<1ms TTL=127
Reply from 192.168.20.11: bytes=32 time<1ms TTL=127
Ping statistics for 192.168.20.11:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Test POS-07: Central WAN Router Reachability#
From PC-VLAN10 Command Prompt, ping R1-HQ WAN interface 10.0.0.1:
ping 10.0.0.1
Expected Output:
Ping statistics for 10.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
2. Negative Verification (Starter Fault Diagnosis)#
Test NEG-01: Faulty Relay Helper Address on VLAN 10 Subinterface#
In the starter state, check R2-Branch subinterface configuration:
R2-Branch# show running-config interface GigabitEthernet0/1.10
!
interface GigabitEthernet0/1.10
encapsulation dot1Q 10
ip address 192.168.10.1 255.255.255.0
ip helper-address 10.0.0.5
end
When PC-VLAN10 broadcasts DHCP Discover packets, R2-Branch relays them to 10.0.0.5, an unreachable IP address.
From PC-VLAN10:
C:\> ipconfig /renew
DHCP request failed.
Criteria: PC-VLAN10 fails to obtain an IP lease and reverts to 0.0.0.0 or 169.254.x.x.
Test NEG-02: DHCP Pool Subnet Mismatch on Central Server#
In the starter state, check R1-HQ DHCP pool configuration:
R1-HQ# show ip dhcp pool POOL_VLAN20
Pool POOL_VLAN20 :
Utilization mark (high/low) : 100 / 0
Subnet size (lines) : 1
Total addresses : 254
Leased addresses : 0
Excluded addresses : 1
Pending event : none
192.168.200.0 /24
When R2-Branch receives a broadcast on GigabitEthernet0/1.20, it properly forwards the request to 10.0.0.1 with giaddr = 192.168.20.1. However, R1-HQ has no pool configured for the 192.168.20.0/24 subnet. It silently discards the relay packet.
From PC-VLAN20:
C:\> ipconfig /renew
DHCP request failed.
Criteria: PC-VLAN20 fails to obtain an IP lease until POOL_VLAN20 is corrected with network 192.168.20.0 255.255.255.0.