Firewall interview questions

The following are interview questions based on Firewalls.

firewall interview questions

These questions are preview from ebook – 250 Networking Interview questions and answers

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Interview question 1

Q1 What happens when a TCP based packet returns to a NAT firewall

When a TCP packet which exited the NAT firewall returns, the firewall looks into the destination port in the TCP header. It would then identify the appropriate entry in the NAT table which has the corresponding entry. After the packet is identified, the destination IP address in the IP packet which now contains the IP address of the NAT firewall would be re-written with the actual initiators IP address, following which the packet is sent to the intended recipient

Q2 What happens when a TCP based packet exits a NAT firewall

When a TCP packet exits a NAT firewall, the source port and destination port number in the TCP header along with the source and destination IP address in the IP header is added to the Network address translation table. After this operation is performed, the source IP address in the IP header is re-written with the IP address of the NAT firewall following which the packet exits the firewall.

Q3 Which protocol would you block on a firewall for blocking tracert

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Q4 PC1 PC2 and PC3 are connected to the internet via a NAT router which does port address translation. If the three PC’s simultaneously initiate a HTTP session with the web server, explain how the NAT router would handle the communication

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Q5 If NAT is configured for internet sharing on a router, is it required to setup additional routing for forwarding packets to the internet or would NAT take care of the same

NAT and routing are two different concepts. NAT would not perform routing for the packet, which it has translated. The router should be setup for additional routing as to how to forward the packet. A default route would ensure that all unknown packets are forwarded to the internet.

Q6 If PAT is configured on the router, would it also take care of the packets be forwarded automatically to the internet

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Q7 How can web access be blocked for a specific group of users on a network with a firewall.

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