What methods can be used to prevent Denial of Service (DoS) attacks on a router?

Several methods can be used to prevent DoS attacks on a router:

• Traffic filtering: configuring ACLs (Access Control Lists) to block suspicious IP addresses or traffic types.
• Rate Limiting: limiting the number of packets or connections from a single source.
• Using firewalls and IDS/IPS: to detect and block anomalous traffic.
• Updating firmware and patches: to close known vulnerabilities.
• Load balancing: using load balancers to distribute traffic.

For example, on a Cisco router, you can configure rate-limit on an interface:

interface GigabitEthernet0/1
  ip address 192.168.1.1 255.255.255.0
  rate-limit input access-group 101 8000 1500 1500 conform-action transmit exceed-action drop
!
access-list 101 permit ip any any

This will limit incoming traffic, helping to prevent device overload.