What’s Asymmetric Routing? Dealing with Two ENIs and Asymmetric Routing on AWS EC2 Linux instances
Asymmetric Routing on AWS EC2. Attaching two or more network interfaces (ENIs) from the same subnet to a non-Amazon Linux EC2 instance (for example, CentOS or RedHat Linux) might encounter traffic flow issues caused by asymmetric routing and Linux settings. The solution is to utilize iproute2 package two-phase routing infrastructure. First, we need to create two routing rules that select the routing table that sends the server's response traffic out the same interface on which the request arrived. Second, we create two routing tables; each table routes out through a different interface. The source address of the outgoing packets can be used for the route rules as the selector.
