Service Manual

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: Dynamic ARP inspection (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 prole allocates only nine entries to the L2SysFlow region for DAI. You can congure 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; L2SystemFlow has 15 entries. Six L2SystemFlow entries are used by Layer 2 protocols, leaving nine
for DAI. L2Protocol can have a maximum of 100 entries; you must expand this region 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 seven more entries; in this case, recongure the SystemFlow region for 122 entries using the layer-2 eg-
acl value fib value frrp value ing-acl value learn value l2pt value qos value system-
flow 122 command.
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 nine are for
DAI; to enable DAI on 16 VLANs, seven more entries are required. 87 L2Protocol + 13 additional L2Protocol + 15 L2SystemFlow
+ 7 additional L2SystemFlow equals 122.
Conguring Dynamic ARP Inspection
To enable dynamic ARP inspection, use the following commands.
1. Enable DHCP snooping.
2. Validate ARP frames against the DHCP snooping binding table.
INTERFACE VLAN mode
arp inspection
Examples of Viewing the ARP Database and Packets
To view entries in the ARP database, use the show arp inspection database command.
Dell#show arp inspection database
Protocol Address Age(min) Hardware Address Interface VLAN CPU
---------------------------------------------------------------------
Internet 10.1.1.251 - 00:00:4d:57:f2:50 Gi 1/2 Vl 10 CP
Internet 10.1.1.252 - 00:00:4d:57:e6:f6 Gi 1/1 Vl 10 CP
Internet 10.1.1.253 - 00:00:4d:57:f8:e8 Gi 1/3 Vl 10 CP
Internet 10.1.1.254 - 00:00:4d:69:e8:f2 Gi 1/5 Vl 10 CP
Dell#
To see how many valid and invalid ARP packets have been processed, use the show arp inspection statistics command.
Dell#show arp inspection statistics
Dynamic ARP Inspection (DAI) Statistics
---------------------------------------
Valid ARP Requests : 0
Valid ARP Replies : 1000
Invalid ARP Requests : 1000
Invalid ARP Replies : 0
Dell#
252
Dynamic Host Conguration Protocol (DHCP)