Port Security for EX Series Switches Overview

Juniper Networks Junos operating system (Junos OS) on Juniper Networks EX Series Ethernet Switches provides features to help secure ports on the switch. The ports can be categorized as either trusted or untrusted. You apply policies appropriate to those categories to protect against various types of attacks.

Port security features can be turned on to obtain the most robust port security level. Basic port security features are enabled in the switch's default configuration. You can configure additional features with minimal configuration steps.

Depending on the particular feature, you can configure the port security feature either on:

• VLANs—A specific VLAN or all VLANs
• Interfaces—A specific interface or all interfaces

Note: If you configure one of the port security features on all VLANs or all interfaces, the switch software enables that port security feature on all VLANs and all interfaces that are not explicitly configured with other port security features. However, if you do explicitly configure one of the port security features on a specific VLAN or on a specific interface, you must explicitly configure any additional port security features that you want to apply to that VLAN or interface. Otherwise, the switch software automatically applies the default values for the feature. For example, if you enable DHCP snooping on all VLANs and decide to explicitly enable IP source guard only on a specific VLAN, you must also explicitly enable DHCP snooping on that specific VLAN. Otherwise, the default value of no DHCP snooping applies to that VLAN.

• DHCP option 82—Also known as the DHCP relay agent information option. Helps protect the switch against attacks such as spoofing of IP addresses and MAC addresses and DHCP IP address starvation. Option 82 provides information about the network location of a DHCP client, and the DHCP server uses this information to implement IP addresses or other parameters for the client.
• DHCP snooping—Filters and blocks ingress DHCP server messages on untrusted ports; builds and maintains an IP-address/MAC-address binding database (called the DHCP snooping database). You enable this feature on VLANs.
• Dynamic ARP inspection (DAI)—Prevents ARP spoofing attacks. ARP requests and replies are compared against entries in the DHCP snooping database, and filtering decisions are made based on the results of those comparisons. You enable this feature on VLANs.
• IP source guard—Mitigates the effects of IP address spoofing attacks on the Ethernet LAN. With IP source guard enabled, the source IP address in the packet sent from an untrusted access interface is validated against the source MAC address in the DHCP snooping database. The packet is forwarded if the source IP address to source MAC address binding is valid; if the binding is not valid, the packet is discarded. You enable this feature on VLANs.
• MAC limiting—Protects against flooding of the Ethernet switching table (also known as the MAC forwarding table or Layer 2 forwarding table). You enable this feature on access interfaces (ports).
• MAC move limiting—Detects MAC movement and MAC spoofing on access ports. You enable this feature on VLANs.
• Persistent MAC learning—Also known as sticky MAC. Allows dynamically learned MAC addresses to be retained on an interface across restarts of the switch. You enable this feature on interfaces.
• Trusted DHCP server—With a DHCP server on a trusted port, protects against rogue DHCP servers sending leases. You enable this feature on interfaces (ports). By default, access ports are untrusted and trunk ports are trusted. (Access ports are the switch ports that connect to Ethernet endpoints such as user PCs and laptops, servers, and printers. Trunk ports are the switch ports that connect to other Ethernet switches or to routers.)