Cisco 350XG series, Руководство администратора

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Security
ARP Inspection
Cisco 350XG & 550XG Series 10G Stackable Managed Switches 426
19
• Properties
• Interfaces Settings
• Interfaces Settings
• ARP Access Control
• ARP Access Control Rules
• VLAN Settings
How ARP Prevents Cache Poisoning
The ARP inspection feature relates to interfaces as either trusted or untrusted (see
Interfaces Settings page).
Interfaces are classified by the user as follows:
• Trusted — Packets are not inspected.
• Untrusted — Packets are inspected as described above.
ARP inspection is performed only on untrusted interfaces. ARP packets that are
received on the trusted interface are simply forwarded.
Upon packet arrival on untrusted interfaces the following logic is implemented:
• Search the ARP access control rules for the packet's IP/MAC addresses. If
the IP address is found and the MAC address in the list matches the
packet's MAC address, then the packet is valid; otherwise it is not.
• If the packet's IP address was not found, and DHCP Snooping is enabled for
the packet’s VLAN, search the DHCP Snooping Binding database for the
packet's <VLAN - IP address> pair. If the <VLAN - IP address> pair was
found, and the MAC address and the interface in the database match the
packet's MAC address and ingress interface, the packet is valid.
• If the packet's IP address was not found in the ARP access control rules or in
the DHCP Snooping Binding database the packet is invalid and is dropped.
A SYSLOG message is generated.
• If a packet is valid, it is forwarded and the ARP cache is updated.
If the ARP Packet Validation option is selected ( Properties page), the following
additional validation checks are performed: