Understanding Intelligent Uplink Selection

This section describes the definition and purpose of intelligent uplink selection.

Overview

As services expand and diversify, enterprises usually deploy multiple links at the network egress to improve egress link bandwidth and reliability. However, an egress device usually randomly selects a link to forward traffic, and does not consider the actual bandwidth or real-time status of each link. Therefore, the following problems may occur in actual application scenarios.

If each link has different bandwidths, the links with large bandwidths may be idle, and the links with small bandwidth may be congested, wasting link resources.
Because each ISP link provides different transmission quality and requires different service charges, the enterprise sometimes needs to ensure service quality and sometimes to use the link with a low charge. However, equal traffic distribution fails to meet these requirements.
If the link between the egress device and destination device fails or the service on the destination device is unavailable but the traffic is forwarded to the faulty link or destination device with unavailable service, the access fails.

Intelligent uplink selection can solve the preceding problems. When multiple links are available to the destination network, intelligent uplink selection enables the FW to dynamically select the optimal link based on the specified link bandwidths, weights, priorities, or automatically detected link quality, and dynamically adjust the selection result based on the real-time status of each link. In this way, link resource utilization and user experience are improved.

Intelligent Uplink Selection Classification

Intelligent uplink selection is classified into two types:

Outbound link selection: If multiple links to the destination network are available for an intranet user to access the extranet, the FW performs outbound link selection.

**Table 1** Outbound link selection
Category	Definition
Global Route Selection Policy (Outbound Link Selection Based on Equal-cost Routes or Default Routes)	When there are multiple equal-cost routes or default routes to the destination network, the FW dynamically selects the optimal link in different intelligent uplink selection modes.
PBR (PBR-based Outbound Link Selection)	When traffic matches a policy-based route (PBR) configured on the network and multiple links are available to the destination network, the FW dynamically selects the optimal link in different intelligent uplink selection modes.
ISP Link Selection by ISP Routes	When the FW functions as an egress gateway to connect to multiple ISP networks, the FW generates ISP routes in batches to forward traffic destined for a specified ISP network through the corresponding outbound interface. This ensures traffic forwarding through the shortest path. The FW also supports the DNS transparent proxy function. That is, when an intranet user initiates a DNS request to the DNS server for accessing a domain name, the FW modifies the destination address (DNS server address) of the DNS request packet according to the outbound interface specified in the packet that meets the proxy conditions. This prevents most DNS request packets from being transmitted over the same ISP link, avoiding link congestion or inter-ISP access.

Inbound link selection: When an extranet user initiates a DNS request to the intranet DNS server for accessing the intranet server through a domain name, the DNS server returns the resolved address to the extranet user. In this way, the FW intelligently modifies the resolved address in the DNS response so that the user can obtain the most appropriate resolved address to avoid link congestion or inter-ISP access. This mode is also called smart DNS.