N10-009 · Question #269
An ISP provided a company with an IP range of 98.174.235.142/28. A network technician configured a router with a subnet mask of 255.255.255.224 and default gateway of 98.174.235.129. After the…
The correct answer is A. Change the subnet mask to .240. A connectivity issue arises because a router is configured with an incorrect subnet mask, despite being provided with a specific IP range by the ISP.
Question
An ISP provided a company with an IP range of 98.174.235.142/28. A network technician configured a router with a subnet mask of 255.255.255.224 and default gateway of 98.174.235.129. After the configuration was set up. the company is unable to connect to the ISP. Which of the following would resolve this issue?
Options
- AChange the subnet mask to .240.
- BChange the Ethernet cable from the external interface to the modem.
- CChange the CIDR to /29.
- DChange the static IP to 98.174.235.128/28.
How the community answered
(27 responses)- A56% (15)
- B7% (2)
- C22% (6)
- D15% (4)
Why each option
A connectivity issue arises because a router is configured with an incorrect subnet mask, despite being provided with a specific IP range by the ISP.
The ISP provided an IP range with a /28 CIDR, which corresponds to a subnet mask of 255.255.255.240. The technician incorrectly configured the router with a 255.255.255.224 mask (a /27). This mismatch causes the router to misinterpret the network's boundaries and broadcast domain, preventing proper communication with the ISP's equipment; changing the subnet mask to .240 will correct this configuration error.
While an Ethernet cable issue can cause connectivity problems, the described scenario points to a logical misconfiguration (subnet mask mismatch) as the primary cause.
Changing the CIDR to /29 (subnet mask .248) would further deviate from the ISP's provided /28 range and likely exacerbate the connectivity issue.
The given IP 98.174.235.142 and default gateway 98.174.235.129 are valid within a 98.174.235.128/28 subnet; changing the static IP to the network address 98.174.235.128 would render it unusable as a host address.
Concept tested: IP addressing, CIDR, and subnet mask configuration
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr/configuration/xe-16-6/ipaddr-xe-16-6-book/ipaddr-overview.html
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