Cisco CCNA (200-301)IP ServicesMedium
A network administrator is configuring a DHCP server on a Cisco router. They need to exclude the first 10 IP addresses in the 192.168.1.0/24 subnet from being assigned by DHCP. Which command or set of commands accomplishes this?
- Aip dhcp excluded-address 192.168.1.0 192.168.1.9
- Bip dhcp pool VLAN10 network 192.168.1.0 255.255.255.0 excluded-address 192.168.1.0 192.168.1.9
- Cip dhcp excluded-address 192.168.1.1 192.168.1.10
- Dip dhcp pool VLAN10 network 192.168.1.0 255.255.255.0 default-router 192.168.1.1 excluded-address 192.168.1.1 192.168.1.10
Show answer & explanationAnswer & explanation
Correct answer: C. ip dhcp excluded-address 192.168.1.1 192.168.1.10
The `ip dhcp excluded-address` command is used in global configuration mode to specify a range of IP addresses that the DHCP server should not assign. The first 10 addresses in 192.168.1.0/24 are 192.168.1.0 through 192.168.1.9, but 192.168.1.0 is the network address and typically not assignable. Therefore, excluding 192.168.1.1 through 192.168.1.10 correctly excludes the first ten *assignable* host addresses.
Why the other options are wrong
- A. This command correctly specifies the range but starts from 192.168.1.0, which is the network address and generally not assigned anyway. More importantly, it only excludes 10.0.0.0 through 10.0.0.9 (ten addresses). The question states 'first 10 IP addresses', which for a /24 subnet typically means 10.0.0.1 to 10.0.0.10, assuming 10.0.0.0 is the network address.
- B. The `excluded-address` command is a global configuration command, not a sub-command under `ip dhcp pool`.
- D. Like option B, `excluded-address` is incorrectly placed within the `ip dhcp pool` configuration. The range itself (192.168.1.1 to 192.168.1.10) is correct for excluding the first 10 assignable IPs.
DHCP Excluded Addresses
Specifying IP addresses within a DHCP pool range that should not be assigned to clients.
- Configured using `ip dhcp excluded-address <start_IP> <end_IP>` in global config mode.
- Used for static assignments (servers, routers) or reserved addresses.
- Ensures no IP conflicts with dynamically assigned addresses.
Memory trick: Exclude a range of addresses from the DHCP party.