Dell Force10 S4810P Configuration Manual page 392

• denial of service—an attacker can send a fraudulent ARP messages to a client to associate a false
MAC address with the gateway address, which would blackhole all internet-bound packets from the
client.
Note: DAI uses entries in the L2SysFlow CAM region, a sub-region of SystemFlow. One CAM entry is
required for every DAI-enabled VLAN. You can enable DAI on up to 16 VLANs on a system. However, the
ExaScale default CAM profile allocates only 9 entries to the L2SysFlow region for DAI. You can configure
10 to 16 DAI-enabled VLANs by allocating more CAM space to the L2SysFlow region before enabling
DAI.
SystemFlow has 102 entries by default. This region is comprised of two sub-regions: L2Protocol and
L2SystemFlow. L2Protocol has 87 entries, and L2SystemFlow has 15 entries. Six L2SystemFlow entries
are used by Layer 2 protocols, leaving 9 for DAI. L2Protocol can have a maximum of 100 entries, and this
region must be expanded to capacity before you can increase the size of L2SystemFlow. This is relevant
when you are enabling DAI on VLANs. If, for example, you want to enable DAI on 16 VLANs, you need 7
more entries; in this case, reconfigure the SystemFlow region for 122 entries:
layer-2 eg-acl value fib value frrp value ing-acl value learn value l2pt value qos value system-flow 122
The logic is as follows:
L2Protocol has 87 entries by default and must be expanded to its maximum capacity, 100 entries, before
L2SystemFlow can be increased; therefore 13 more L2Protocol entries are required. L2SystemFlow has
15 entries by default, but only 9 are for DAI; to enable DAI on 16 VLANs, 7 more entries are required. 87
L2Protocol + 13 additional L2Protocol + 15 L2SystemFlow + 7 additional L2SystemFlow equals 122.
Step Task
1 Enable DHCP Snooping.
2 Validate ARP frames against the DHCP Snooping binding table.
View the number of entries in the ARP database with the
FTOS#show arp inspection database
Protocol
----------------------------------------------------------------------------
Internet
Internet
Internet
Internet
FTOS#
392
| Dynamic Host Configuration Protocol (DHCP)
Address Age(min)
10.1.1.251
10.1.1.252
10.1.1.253
10.1.1.254
Command Syntax
arp inspection
show arp inspection database
Hardware Address
- 00:00:4d:57:f2:50
- 00:00:4d:57:e6:f6
- 00:00:4d:57:f8:e8
- 00:00:4d:69:e8:f2
Command Mode
INTERFACE VLAN
command.
Interface VLAN CPU
Gi 0/2 Vl 10 CP
Gi 0/1 Vl 10 CP
Gi 0/3 Vl 10 CP
Te 0/50 Vl 10 CP