Implementing Port Security in Junos: Mac Limiting and IP Source Guard


As networks evolve, so do security threats. A primary concern for network engineers is the security of access layer switches. Unauthorized devices or users can pose significant risks if allowed unchecked access. Junos OS provides a robust suite of port security features, with Mac Limiting and IP Source Guard at the forefront. Dive into this guide as we explore these features and their implementation in Junos OS.

1. MAC Limiting

MAC Limiting in Junos restricts the number of MAC addresses learned on a port, preventing MAC flooding attacks and ensuring only authorized devices can access the network.

Key Features:

Configuring MAC Limiting:

user@switch# set ethernet-switching-options secure-access-port interface [interface-name] mac-limit [number] action [action-type]

Where [action-type] can be drop, log, none, or shutdown.

2. IP Source Guard

IP Source Guard helps prevent IP spoofing attacks by ensuring that traffic received from a client matches its DHCP-assigned IP address.

Key Features:

Configuring IP Source Guard:

Enable IP Source Guard on an interface:

user@switch# set ethernet-switching-options secure-access-port interface [interface-name] ip-source-guard

For static IP assignments:

user@switch# set ethernet-switching-options secure-access-port ip-source-guard static-bindings [ip-address] mac [mac-address]

3. Monitoring and Troubleshooting

Display MAC Limiting Information:

user@switch> show ethernet-switching table brief

Verify IP Source Guard Configuration:

user@switch> show ethernet-switching-options secure-access-port summary

Best Practices:

  1. Audit Regularly: Periodically check the configuration to ensure there aren't any unintentional open ports.
  2. Consistent Deployment: Apply security measures consistently across all access switches.
  3. Monitor Logs: Regularly review logs to identify and respond to any security breaches.


Port security is a critical line of defense in protecting the integrity of network infrastructures. MAC Limiting and IP Source Guard in Junos OS are just a fraction of the many tools available to network engineers. Implementing them ensures not just a secure but also a reliable network experience for authorized users.

Stay ahead of threats and ensure your network remains robust and secure. Join us in our next post as we continue our deep dive into Junos OS and its plethora of features. Secure networking to all!

© Ben Jacobson.RSS