Troubleshooting Slow Internet on AR Routers: Common Causes and Solutions

First, verify whether the CPU is overloaded by running display cpu-usage and examine logs with display log; alerts may indicate packet drops and CPU overload.

1. TCP MSS abnormal negotiation can cause slow internet, especially in PPPoE environments. The recommended fix is to set the uplink port TCP MSS to 1400 using tcp adjust 1400.

2. Traffic reaching device performance limits should be checked by monitoring CPU usage with display cpu-usage. If the router is at its performance ceiling, consider traffic shaping or limiting low‑priority flows.

3. Insufficient uplink bandwidth requires checking interface bandwidth peak statistics and, if necessary, coordinating with the ISP to test uplink speed.

4. Link negotiation problems are diagnosed with display th interface; ensure the port is in full‑duplex mode and the speed is correct. If negotiation fails, disable auto‑negotiation ( undo negotiation auto) and manually set duplex full and speed 100/1000.

5. NAT resource exhaustion can be identified by the number of NAT sessions using display nat session number. Mitigation includes applying firewall policies to limit connections per IP and enabling URPF with urpf strict on the relevant interfaces.

6. Network viruses may manifest as ARP table anomalies (multiple IPs sharing a MAC). Use professional antivirus tools on infected machines and enable strict ARP learning on the router with arp learning strict to prevent ARP spoofing.