Brocade Communications Systems 6650 manual Dynamic ARP Inspection, ARP entries

Dynamic ARP inspection

Dynamic ARP Inspection

Dynamic ARP Inspection (DAI) allows only valid ARP requests and responses to be forwarded. A Brocade device on which DAI is configured does the following:

•Intercepts ARP packets received by the system CPU

•Inspects all ARP requests and responses received on untrusted ports

•Verifies that each of the intercepted packets has a valid IP-to-MAC address binding before updating the local ARP table, or before forwarding the packet to the appropriate destination

•Drops invalid ARP packets

When you enable DAI on a VLAN, by default, all member ports are untrusted. You must manually configure trusted ports. In a typical network configuration, ports connected to host ports are untrusted. You configure ports connected to other switches or routers as trusted.

DAI inspects ARP packets received on untrusted ports, as shown in Figure 16. DAI carries out the inspection based on IP-to-MAC address bindings stored in a trusted binding database. For the Brocade device, the binding database is the ARP table, which supports DAI, DHCP snooping, and IP Source Guard. To inspect an ARP request packet, DAI checks the source IP and source MAC address against the ARP table. For an ARP reply packet, DAI checks the source IP, source MAC, destination IP, and destination MAC addresses. DAI forwards the valid packets and discards those with invalid IP-to-MAC address bindings.

When ARP packets reach a trusted port, DAI lets them through, as shown in Figure 16.

FIGURE 16 Dynamic ARP inspection at work

ARP

packet

Untrusted

DAI

Trusted

ARP

packet

Brocade Switch

ARP entries

DAI uses the IP/MAC mappings in the ARP table to validate ARP packets received on untrusted ports.

ARP entries in the ARP table derive from the following:

•Dynamic ARP – normal ARP learned from trusted ports.

•Static ARP – statically configured IP/MAC/port mapping.

•Inspection ARP – statically configured IP/MAC mapping, where the port is initially unspecified. The actual physical port mapping will be resolved and updated from validated ARP packets.Refer to “Configuring an inspection ARP entry” on page 282.

280	Brocade ICX 6650 Security Configuration Guide
	53-1002601-01