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packet arrived on the correct port. Packets that do not pass this check are forwarded to the server for
validation. This checkpoint prevents an attacker from spoofing a client and declining or releasing the real
client’s address. Server-originated packets (DHCPOFFER, DHCPACK, and DHCPNACK) that arrive on a not
trusted port are also dropped. This checkpoint prevents an attacker from acting as an imposter as a
DHCP server to facilitate a man-in-the-middle attack.
Binding table entries are deleted when a lease expires, or the relay agent encounters a DHCPRELEASE,
DHCPNACK, or DHCPDECLINE.
DHCP snooping is supported on Layer 2 and Layer 3 traffic. DHCP snooping on Layer 2 interfaces does
require a relay agent.
Binding table entries are deleted when a lease expires or when the relay agent encounters a
DHCPRELEASE. Line cards maintain a list of snooped VLANs. When the binding table is exhausted, DHCP
packets are dropped on snooped VLANs, while these packets are forwarded across non-snooped VLANs.
Because DHCP packets are dropped, no new IP address assignments are made. However, DHCPRELEASE
and DHCPDECLINE packets are allowed so that the DHCP snooping table can decrease in size. After the
table usage falls below the maximum limit of 4000 entries, new IP address assignments are allowed.
NOTE: DHCP server packets are dropped on all not trusted interfaces of a system configured for
DHCP snooping. To prevent these packets from being dropped, configure
ip dhcp snooping
trust
on the server-connected port.
Enabling DHCP Snooping
To enable DHCP snooping, use the following commands.
1.
Enable DHCP snooping globally.
CONFIGURATION mode
ip dhcp snooping
2.
Specify ports connected to DHCP servers as trusted.
INTERFACE mode
INTERFACE PORT EXTENDER mode
ip dhcp snooping trust
3.
Enable DHCP snooping on a VLAN.
CONFIGURATION mode
ip dhcp snooping vlan
name
Enabling IPv6 DHCP Snooping
To enable IPv6 DHCP snooping, use the following commands.
1.
Enable IPv6 DHCP snooping globally.
CONFIGURATION mode
ipv6 dhcp snooping
2.
Specify ports connected to IPv6 DHCP servers as trusted.
INTERFACE mode
Dynamic Host Configuration Protocol (DHCP)
299
Summary of Contents for S6000-ON
Page 1: ...Dell Configuration Guide for the S6000 ON System 9 9 0 0 ...
Page 557: ...Figure 80 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 557 ...
Page 562: ...Figure 83 MSDP Default Peer Scenario 1 562 Multicast Source Discovery Protocol MSDP ...
Page 563: ...Figure 84 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 563 ...
Page 564: ...Figure 85 MSDP Default Peer Scenario 3 564 Multicast Source Discovery Protocol MSDP ...
Page 665: ...Policy based Routing PBR 665 ...
Page 818: ...Figure 110 Single and Double Tag TPID Match 818 Service Provider Bridging ...
Page 819: ...Figure 111 Single and Double Tag First byte TPID Match Service Provider Bridging 819 ...
Page 995: ...Figure 140 Setup OSPF and Static Routes Virtual Routing and Forwarding VRF 995 ...