What are the common methods used to bypass or circumvent firewalls?

There are several common methods used to bypass or circumvent firewalls, including:

1. Tunneling: This involves encapsulating the restricted traffic within a different protocol that is allowed by the firewall, such as using a Virtual Private Network (VPN) or Secure Shell (SSH) tunnel.

2. Port hopping: This technique involves using non-standard or uncommon ports for communication, making it difficult for the firewall to detect and block the traffic.

3. Application layer attacks: Attackers may exploit vulnerabilities in specific applications or protocols to bypass firewalls. For example, using HTTP or HTTPS to disguise malicious traffic as regular web traffic.

4. Proxy servers: By using proxy servers, attackers can route their traffic through an intermediate server that is not blocked by the firewall, effectively bypassing its restrictions.

5. IP spoofing: This involves forging the source IP address of the traffic to make it appear as if it is coming from an allowed source, thus tricking the firewall into allowing it.

6. Domain Name System (DNS) tunneling: Attackers can use DNS requests and responses to transfer data, bypassing the firewall's inspection of traditional network traffic.

It is important for organizations to regularly update and configure their firewalls to mitigate these bypassing techniques and ensure effective network security.