When organizations require dedicated and reliable internet connectivity, they often turn to Internet Service Providers (ISPs) for Dedicated Internet Access (DIA) solutions. These solutions typically leverage the Border Gateway Protocol (BGP) for routing between the customer’s and ISP’s networks. A critical aspect of this setup is the management of routing tables, which determine how traffic is routed across the internet. ISPs typically offer several routing table management options, each with advantages and trade-offs.
Default Route + Partial Routing Table: A Balanced Approach
One of the most common setups ISPs offers is a combination of a default route and a partial routing table. This approach balances routing control, performance, and resource requirements on the customer’s router.
The Default Route (0.0.0.0/0)
The default route is a catch-all for all internet destinations not covered by more specific routes. It requires minimal resources on the customer’s router and allows basic internet connectivity with rudimentary path selection.
The Partial Routing Table
The partial routing table includes routes for popular networks, major destinations, and local prefixes. Compared to just the default route, it provides more control over path selection for critical traffic. However, it doesn’t require as much router memory and CPU resources as the full internet routing table.
By combining these two components, organizations can enjoy:
- Basic internet reachability via the default route.
- Improved routing control and optimization for important traffic using the partial routes.
- Better convergence times compared to using only a default route.
- Lower resource overhead compared to maintaining the full internet routing table.
ISPs often recommend this hybrid approach as it strikes a reasonable balance for most enterprise customers using BGP/DIA links.
Other Routing Table Options
While the default + partial routing table setup is common, ISPs also offer additional options to cater to specific performance, control, or policy requirements:
Full Internet Routing Table
The ISP provides the entire global internet routing table, containing hundreds of thousands or even millions of routes. This option suits large enterprises requiring maximum routing control and flexibility but demands substantial memory and CPU resources on the customer’s router.
Customer-Defined Routing Table
Some ISPs allow customers to specify the prefixes or networks they want to receive routes for, providing a customized routing table based on their specifications. This option suits organizations with specific routing needs or policies but requires effort to define and maintain the desired routing table.
Backup/Secondary Link Options
ISPs may offer different routing table options for primary and secondary/backup links. For example, the primary link might receive the full internet routing table. In contrast, the secondary link could receive a default route or a partial routing table to ensure network resilience and failover capabilities.
Evaluation Considerations
When evaluating routing table options, organizations should consider their network complexity, traffic patterns, performance requirements, and available router resources. Additionally, they should assess the level of routing control required, convergence time expectations, memory requirements, and the overall impact on network performance and path selection.
By understanding the various routing table management options ISPs offer and their respective advantages and trade-offs, organizations can make informed decisions that align with their specific needs and optimize their dedicated internet connectivity solutions.