Dell BigIron RX Series, Руководство по настройке

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BigIron RX Series Configuration Guide 1001
53-1002253-01
Chapter
35
Inspecting and Tracking DHCP Packets
For enhanced network security, you can configure the Brocade device to inspect and keep track of
Dynamic Host Configuration Protocol (DHCP) assignments. To do so, use the following features.
Dynamic ARP inspection
NOTE
This feature is only supported on Layer 3 code.
Dynamic ARP Inspection (DAI) enables the Brocade device to intercept and examine all ARP request
and response packets in a subnet and discard those packets with invalid IP to MAC address
bindings. DAI can prevent common man-in-the-middle (MiM) attacks such as ARP cache poisoning,
and disallow mis-configuration of client IP addresses.
ARP attacks
ARP provides IP communication within a Layer 2 broadcast domain by mapping an IP address to a
MAC address. Before a host can talk to another host, it must map the IP address to a MAC address
first. If the host does not have the mapping in its ARP table, it sends an ARP request to resolve the
mapping. All computers on the subnet will receive and process the ARP requests, and the host
whose IP address matches the IP address in the request will send an ARP reply.
An ARP poisoning attack can target hosts, switches, and routers connected to the Layer 2 network
by poisoning the ARP caches of systems connected to the subnet and by intercepting traffic
intended for other hosts on the subnet. For instance, a malicious host can reply to an ARP request
with its own MAC address, thereby causing other hosts on the same subnet to store this
information in their ARP tables or replace the existing ARP entry. Furthermore, a host can send
gratuitous replies without having received any ARP requests. A malicious host can also send out
ARP packets claiming to have an IP address that actually belongs to another host (e.g. the default
router). After the attack, all traffic from the device under attack flows through the attacker’s
computer and then to the router, switch, or host.
TABLE 165 Chapter contents
Description See page
Dynamic ARP Inspection – Intercepts and examines all ARP request and response
packets in a subnet, and blocks all packets that have invalid IP to MAC address bindings page 1001
DHCP Snooping – Filters replay DHCP packets from untrusted ports (those connected to
host ports), and allows DHCP packets from trusted ports (those connected to DHCP
servers) page 1006
IP Source Guard – Permits traffic with valid source IP addresses only, which is learned
from Dynamic ARP Inspection or DHCP snooping page 1010