Dell S6000 FTOS 9.0(2.0) Configuration Guide for the System - Page 252

www.dell.com | support.dell.com Packets received on snooping disabled L3 Ports : 0 Snooping packets processed on L2 vlans : 142 DHCP Binding File Details Invalid File Invalid Binding Entry Binding Entry lease expired List of Trust Ports List of DHCP Snooping Enabled Vlans List of DAI Trust ports : 0 : 0 : 0 :Te 0/49 :Vl 10 :Te 0/49 Drop DHCP packets on snooped VLANs only Binding table entries are deleted when a lease expires, or the relay agent encounters a DHCPRELEASE. Starting with FTOS Release 8.2.1.1, line cards maintain a list of snooped VLANs. When the binding table fills, DHCP packets are dropped only on snooped-VLANs, while such packets will be forwarded across non-snooped VLANs. Since DHCP packets are dropped, no new IP address assignments are made. However, DHCP Release and Decline packets are allowed so that the DHCP snooping table can decrease in size. Once the table usage falls below the max limit of 4000 entries, new IP address assignments are allowed. View the number of entries in the table with the show ip dhcp snooping binding command. This output displays the snooping binding table created using the ACK packets from the trusted port. FTOS#show ip dhcp snooping binding Codes : S - Static D - Dynamic IP Address MAC Address Expires(Sec) Type VLAN Interface 10.1.1.251 00:00:4d:57:f2:50 172800 D Vl 10 Te 0/2 10.1.1.252 00:00:4d:57:e6:f6 172800 D Vl 10 Te 0/1 10.1.1.253 00:00:4d:57:f8:e8 172740 D Vl 10 Te 0/3 10.1.1.254 00:00:4d:69:e8:f2 172740 D Vl 10 Te 0/50 Total number of Entries in the table : 4 Dynamic ARP Inspection Dynamic ARP inspection prevents ARP spoofing by forwarding only ARP frames that have been validated against the DHCP binding table. ARP is a stateless protocol that provides no authentication mechanism. Network devices accepts ARP request and replies from any device, and ARP replies are accepted even when no request was sent. If a client receives an ARP message for which a relevant entry already exists in its ARP cache, it overwrites the existing entry with the new information. The lack of authentication in ARP makes it vulnerable to spoofing. ARP spoofing is a technique attackers use to inject false IP to MAC mappings into the ARP cache of a network device. It is used to launch man-in-the-middle (MITM), and denial-of-service (DoS) attacks, among others. 230 | Dynamic Host Configuration Protocol (DHCP)