Chapter 8
| General Security Measures
DHCP Snooping
– 243 –
an untrusted interface (as specified by the
no
ip dhcp snooping trust
command) from a device not listed in the DHCP snooping table will be
dropped.
◆
When enabled, DHCP messages entering an untrusted interface are filtered
based upon dynamic entries learned via DHCP snooping.
◆
Table entries are only learned for trusted interfaces. Each entry includes a MAC
address, IP address, lease time, VLAN identifier, and port identifier.
◆
Filtering rules are implemented as follows:
■
If global DHCP snooping is disabled, all DHCP packets are forwarded.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, all DHCP packets are forwarded for a
trusted
port. If the received packet is a DHCP ACK message, a dynamic DHCP
snooping entry is also added to the binding table.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, but the port is
not trusted
, it is processed as
follows:
■
If the DHCP packet is a reply packet from a DHCP server (including
OFFER, ACK or NAK messages), the packet is dropped.
■
If the DHCP packet is from a client, such as a DECLINE or RELEASE
message, the switch forwards the packet only if the corresponding
entry is found in the binding table.
■
If the DHCP packet is from client, such as a DISCOVER, REQUEST,
INFORM, DECLINE or RELEASE message, the packet is forwarded if MAC
address verification is disabled (as specified by the
ip dhcp snooping
verify mac-address
command). However, if MAC address verification is
enabled, then the packet will only be forwarded if the client’s hardware
address stored in the DHCP packet is the same as the source MAC
address in the Ethernet header.
■
If the DHCP packet is not a recognizable type, it is dropped.
■
If a DHCP packet from a client passes the filtering criteria above, it will only
be forwarded to trusted ports in the same VLAN.
■
If a DHCP packet is from server is received on a trusted port, it will be
forwarded to both trusted and untrusted ports in the same VLAN.
◆
If DHCP snooping is globally disabled, all dynamic bindings are removed from
the binding table.
Содержание EX-3524
Страница 2: ......
Страница 28: ...Figures 28 ...
Страница 34: ...Section I Getting Started 34 ...
Страница 58: ...Chapter 1 Initial Switch Configuration Setting the System Clock 58 ...
Страница 72: ...Chapter 2 Using the Command Line Interface CLI Command Groups 72 ...
Страница 156: ...Chapter 5 SNMP Commands Notification Log Commands 156 ...
Страница 164: ...Chapter 6 Remote Monitoring Commands 164 ...
Страница 218: ...Chapter 7 Authentication Commands Management IP Filter 218 ...
Страница 268: ...Chapter 8 General Security Measures Port based Traffic Segmentation 268 ...
Страница 292: ...Chapter 9 Access Control Lists ACL Information 292 ...
Страница 312: ...Chapter 10 Interface Commands Power Savings 312 ...
Страница 324: ...Chapter 11 Link Aggregation Commands Trunk Status Display Commands 324 ...
Страница 366: ...Chapter 15 Address Table Commands 366 ...
Страница 428: ...Chapter 17 VLAN Commands Configuring Voice VLANs 428 ...
Страница 572: ...Chapter 25 IP Interface Commands IPv6 Interface 572 ...
Страница 578: ...Section I Appendices 578 ...
Страница 594: ...Appendix C Customer Support Manuals 594 ...