BGP route selection may not always be the optimal path to the destination as the protocol does not take into consideration latency, congestion, or jitter. As a result, your traffic may be routed over a suboptimal path. The path that BGP chooses may need to be overwritten with a better path. Path selection can be prioritized based on speed, latency, or cost. You may want to favor one ISP over another based on these metrics.
In Chapter 1, “Edge Networking,” and Chapter 8, “Inter-VPC and Multi-Account Networking,” software-defined wide-area networking (SD-WAN) was discussed, and you learned that SD-WAN offers automated dynamic routing. The AWS Cloud WAN is a single point of routing control that provides a single dashboard for monitoring and event displays. Cloud WAN offers dynamic routing that can be integrated with SD-WAN vendors such as Cisco, DXC, VMware Fortinet, and others in the AWS Marketplace.
Route 53 has DNS policy extensions that enable you to effect routing based on multiple criteria that you specify. When you create a record in Route 53, you choose the routing policy, which determines how Route 53 responds to queries including active-passive failover, geolocation that routes traffic based on the location of your users, and geo-proximity routes traffic based on the location of your resources that can shift traffic from resources in one location to resources in another. Latency-based forwarding directs traffic to the AWS region that provides the lowest latency from the user’s location. When you want Route 53 to respond to DNS queries with up to eight healthy A records selected at random, use the multivalue routing policy. The weighted routing policy is used to route traffic to multiple resources based on weighted percentages that you specify in the configuration.
By optimizing dynamic routing in your enterprise and AWS, networks can help to improve the efficiency, scalability, and availability of your network. By using a combination of dynamic routing protocols, you can ensure that traffic is routed to the best possible destination, improving performance and reducing the risk of network congestion. The AWS Well-Architected Framework series of documents provides years of accumulated knowledge that is a valuable reference. This includes the performance efficiency pillars for network architecture selection at https://docs.aws.amazon.com/wellarchitected/latest/performance-efficiency-pillar/networrk-architecture-selection.html.
AWS allows you to use static routing to optimize network routing. Static routing is a routing method where the network administrator manually enters the routing information into the routing table in place of using a dynamic routing protocol such as BGP. By using static routing, you can ensure that traffic is routed to the best possible destination and this improves the efficiency, scalability, and security of your network; enhances performance; and reduces the risk of network congestion.
Static routes are configured using the ip route command in most common router command parsers.
The command takes the following syntax:
ip route destination-network mask {next-hop-address | interface} [administrative-distance]
For example, the following command configures a static route to the network 192.168.50.0/24, with a next hop of 172.16.1.1:
ip route 192.168.50.0 255.255.255.0 172.16.1.1 250
This command instructs the router that, if a packet has a destination IP address in the 192.168.50.0 subnet, it should forward it out its egress interface that is connected to 172.16.1.1 if it has the lowest administrative distance. Static routes are configured using the web interface, APIs, the CLI, or SDKs.
In a dynamic routing environment, static routes should be used as a last resort, since they can become stale or out-of-date quickly, and if they are not updated, they can cause routing loops or traffic blackholes. The configuring and maintaining many static routes can become a time-consuming and error-prone process, and dynamic routing protocols like OSPF or BGP are more appropriate.
Static routing configuration examples are available in various AWS documentation including how to set up static routing over a site-to-site VPN at https://docs.aws.amazon.com/vpn/latest/s2svpn/cgw-static-routing-examples.html.
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