Asymmetric routing is a network topology where the incoming and outgoing traffic does not follow the same path. Palo Alto Networks is a popular provider of network security solutions that supports asymmetric routing as part of their Layer 3 technologies.
In asymmetric routing, packets travel from one source to a destination via different paths. This topology is usually used to boost network performance, but it presents a challenge for firewall systems. A security device like Palo Alto Networks must be able to track and verify the incoming traffic so it can apply the correct policy.
Palo Alto Networks leverages different algorithms to handle asymmetric routing. These algorithms include:
1. Session Stateful Flow Tracking
Session stateful flow tracking refers to a mechanism that enables Palo Alto Networks to examine traffic patterns and save information about established connections. When a packet arrives on an interface, the firewall verifies whether there is an existing session state. If it exists, the firewall uses the session state information to evaluate packets. In cases when the packet does not match any session state information, the firewall creates a new one.
2. Reverse-path Forwarding (RPF)
Reverse-path forwarding is a widely-used algorithm for handling asymmetric routing. This algorithm checks the IP address of incoming packets against the routing table to verify whether the packet is coming from a valid network path. If the source IP address is not valid, then the packet will be dropped.
3. Virtual Routers (VRs)
Virtual routers are used to route packets with different source and destination. Palo Alto Networks uses VRs to route packets to the correct interface within the device.
4. Active-Active Clusters
Active-active clustering is another algorithm that Palo Alto Networks uses to mitigate the impact of asymmetric routing on the security solution. Active-active clusters enable multiple gateway devices to work together as a single logical entity. Each device can handle a subset of the total network traffic, which reduces the impact of asymmetric routing.
Understanding asymmetric routing is critical to implementing network security solutions such as Palo Alto Networks. Asymmetric routing can negatively impact the security solution since it can lead to network traffic bypassing network security policies. Palo Alto Networks leverages different algorithms to assure that traffic flow is tracked and validated, which enables it to apply best-fit policies on incoming network traffic for effective network security.