IP-based access control (allow/deny) in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allow access from the IP 192.168.1.10.

Nginx

allow [1];

Drag options to blanks, or click blank then click option'

Alocalhost

Ball

Cdeny all

D192.168.1.10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'deny all' instead of an IP address.

Using 'all' which allows everyone.

Using 'localhost' which is not the target IP.

The allow directive followed by the IP address permits access from that IP.

2fill in blank

medium

Complete the code to deny access from the IP 10.0.0.5.

Nginx

deny [1];

Drag options to blanks, or click blank then click option'

A192.168.0.1

Ball

C10.0.0.5

Dlocalhost

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'all' which blocks everyone.

Using a wrong IP address.

Using 'localhost' which is not the target IP.

The deny directive followed by the IP blocks access from that IP.

3fill in blank

hard

Fix the error in the code to allow only the IP 172.16.0.2 and deny all others.

Nginx

allow [1];
deny all;

Drag options to blanks, or click blank then click option'

A172.16.0.2

Blocalhost

Call

D0.0.0.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'allow all;' which allows everyone.

Using an incorrect IP address.

Omitting the 'deny all;' line.

To allow only one IP, use allow with that IP and then deny all; to block others.

4fill in blank

hard

Fill both blanks to allow 192.168.0.0/24 subnet and deny all others.

Nginx

allow [1];
deny [2];

Drag options to blanks, or click blank then click option'

A192.168.0.0/24

Ball

C0.0.0.0/0

Dlocalhost

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'deny 0.0.0.0/0;' which is invalid in this context.

Using 'allow all;' which allows everyone.

Using 'deny localhost;' which does not block all others.

Use allow 192.168.0.0/24; to allow the subnet and deny all; to block others.

5fill in blank

hard

Fill all three blanks to allow 10.1.1.0/24 subnet, deny 10.1.1.100, and deny all others.

Nginx

deny [1];
allow [2];
deny [3];

Drag options to blanks, or click blank then click option'

A10.1.1.0/24

B10.1.1.100

Call

Dlocalhost

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the order of allow and deny directives.

Using 'deny localhost;' which does not block all others.

Omitting the final 'deny all;' line.

First deny the specific IP, then allow the subnet, and finally deny all others.

Practice

1. What does the allow directive do in an nginx configuration?

easy

A. It permits access to specified IP addresses or ranges.

B. It blocks access to specified IP addresses or ranges.

C. It redirects users to another URL.

D. It logs the IP addresses of visitors.

Solution

1. Step 1: Understand the purpose of allow

   The allow directive in nginx is used to specify which IP addresses or ranges are permitted to access the server or location.

2. Step 2: Compare with other directives

   Unlike deny which blocks IPs, allow explicitly permits them.

3. Final Answer:

   It permits access to specified IP addresses or ranges. -> Option A

4. Quick Check:

   allow means permit access [OK]

Hint: Allow means permit access, deny means block access [OK]

Common Mistakes:

• Confusing allow with deny
• Thinking allow redirects users
• Assuming allow logs IPs

2. Which of the following is the correct syntax to deny access to IP 192.168.1.10 in nginx?

easy

A. allow 192.168.1.10;

B. deny 192.168.1.10;

C. block 192.168.1.10;

D. reject 192.168.1.10;

Solution

1. Step 1: Identify the correct directive for blocking IPs

   In nginx, the directive to block or deny access is deny.

2. Step 2: Check syntax correctness

   The correct syntax is deny IP_address; with a semicolon at the end.

3. Final Answer:

   deny 192.168.1.10; -> Option B

4. Quick Check:

   deny blocks IP = deny 192.168.1.10; [OK]

Hint: Use 'deny IP;' to block access in nginx [OK]

Common Mistakes:

• Using 'allow' instead of 'deny'
• Using invalid directives like 'block' or 'reject'
• Missing semicolon at the end

3. Given this nginx config snippet inside a location /admin block:

allow 10.0.0.0/24;
deny all;

What happens when a user with IP 10.0.0.15 tries to access /admin?

medium

A. Access is denied because the IP is not explicitly allowed.

B. Access is denied because deny all overrides allow.

C. Access is allowed only if the user has a valid cookie.

D. Access is allowed because the IP is in the allowed range.

Solution

1. Step 1: Understand the order of allow and deny

   nginx checks allow and deny rules in order. If an IP matches an allow rule, access is granted even if deny all follows.

2. Step 2: Check if IP matches allowed range

   IP 10.0.0.15 is inside 10.0.0.0/24, so it matches the allow rule.

3. Final Answer:

   Access is allowed because the IP is in the allowed range. -> Option D

4. Quick Check:

   Allow matched before deny all = access allowed [OK]

Hint: Allow rules take priority before deny all [OK]

Common Mistakes:

• Assuming deny all always blocks
• Ignoring IP range matching
• Thinking cookies affect IP access control

4. You wrote this nginx config inside a server block:

deny 192.168.0.0/16
allow all;

But all IPs are denied access. What is the problem?

medium

A. You need to reload nginx after changes.

B. The order of deny and allow is wrong; allow should come first.

C. Missing semicolon after deny directive causes config error.

D. The IP range 192.168.0.0/16 is invalid.

Solution

1. Step 1: Check syntax for missing semicolons

   nginx requires semicolons at the end of each directive. The deny line is missing a semicolon, causing the config to fail.

2. Step 2: Understand effect of syntax error

   Without proper syntax, nginx may ignore or misinterpret rules, leading to unexpected blocking of all IPs.

3. Final Answer:

   Missing semicolon after deny directive causes config error. -> Option C

4. Quick Check:

   Every directive needs semicolon [OK]

Hint: Always end nginx directives with semicolon [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking order alone causes issue
• Assuming IP range is invalid

5. You want to allow access only from IP 203.0.113.5 and block everyone else for /secure location. Which nginx config snippet achieves this correctly?

hard

A. location /secure {
allow 203.0.113.5;
deny all;
}

B. location /secure {
deny all;
allow 203.0.113.5;
}

C. location /secure {
allow all;
deny 203.0.113.5;
}

D. location /secure {
deny 203.0.113.5;
allow all;
}

Solution

1. Step 1: Understand correct order of allow and deny

   nginx processes allow and deny in order. To allow one IP and block others, allow must come first, then deny all.

2. Step 2: Verify each option

   location /secure {
     allow 203.0.113.5;
     deny all;
   }

   correctly allows 203.0.113.5 then denies all others.

   location /secure {
     deny all;
     allow 203.0.113.5;
   }

   denies all first, so no one is allowed. Options A and D misuse allow and deny directives.

3. Final Answer:

   location /secure { allow 203.0.113.5; deny all; } -> Option A

4. Quick Check:

   Allow specific IP then deny all others [OK]

Hint: Allow first, then deny all to restrict access [OK]

Common Mistakes:

• Reversing allow and deny order
• Allowing all then denying one IP
• Misusing deny and allow directives