Cisco Sg3008 Manual

IP Configuration
IPv4 Management and Interfaces
Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  285
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The following describes how DHCP reply packets are handled when both DHCP 
Snooping and DHCP Relay are enabled
DHCP Snooping Binding Database
DHCP Snooping builds a database (known as the DHCP Snooping Binding 
database) derived from information taken from DHCP packets entering the device 
through trusted ports. 
The DHCP Snooping Binding database...

IP Configuration
IPv4 Management and Interfaces
286 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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The DHCP Snooping Binding database is also used by IP Source Guard and 
Dynamic ARP Inspection features to determine legitimate packet sources.
DHCP Trusted Ports
Ports can be either DHCP trusted or untrusted. By default, all ports are untrusted. 
To create a port as trusted, use the DHCP Snooping Interface Settings page. 
Packets from these ports are...

IP Configuration
IPv4 Management and Interfaces
Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  287
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STEP  6Device forwards DHCPOFFER, DHCPACK, or DHCPNAK.
The following summarizes how DHCP packets are handled from both trusted and 
untrusted ports. The DHCP Snooping Binding database is stored in non-volatile 
memory.
DHCP Snooping Packet Handling
Packet Type Arriving from 
Untrusted Ingress 
InterfaceArriving from Trusted Ingress 
Interface...

IP Configuration
IPv4 Management and Interfaces
288 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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DHCP Snooping Along With DHCP Relay
If both DHCP Snooping and DHCP Relay are globally enabled, then if DHCP 
Snooping is enabled on the clients VLAN, DHCP Snooping rules contained in the 
DHCP Snooping Binding database are applied, and the DHCP Snooping Binding 
database is updated in the clients and DHCP server ’s VLAN, for packets that are 
relayed....

IP Configuration
IPv4 Management and Interfaces
Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  289
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STEP 1Enable DHCP Snooping and/or DHCP Relay in the IP Configuration > DHCP > 
Properties page or in the Security > DHCP Snooping > Properties page.
STEP  2Define the interfaces on which DHCP Snooping is enabled in the IP Configuration 
> DHCP > Interface Settings page.
STEP  3Configure interfaces as trusted or untrusted in the IP Configuration >...

IP Configuration
IPv4 Management and Interfaces
290 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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STEP  2Click Apply. The settings are written to the Running Configuration file.
STEP  3To  d e f i n e  a  D H C P  s e r v e r ,  c l i c k  Add.
STEP  4Enter the IP address of the DHCP server and click Apply. The settings are written 
to the Running Configuration file. 
Interface Settings
In Layer 2, DHCP Relay and Snooping can only be enabled on...

IP Configuration
IPv4 Management and Interfaces
Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  291
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DHCP Snooping Binding Database
See How the DHCP Snooping Binding Database is Built for a description of how 
dynamic entries are added to the DHCP Snooping Binding database.
Note the following points about maintenance of the DHCP Snooping Binding 
database:
•The device does not update the DHCP Snooping Binding database when a 
station moves to...

IP Configuration
DHCP Server
292 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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STEP  3Enter the fields:
•VLAN ID—VLAN on which packet is expected.
•MAC Address—MAC address of packet.
•IP Address—IP address of packet.
•Interface—Unit/Slot/Interface on which packet is expected.
•Ty p e—T h e  p o s s i b l e  f i e l d  v a l u e s  a r e :  
-
Dynamic—Entry has limited lease time.
-
Static—Entry was statically configured. 
•Lease Time—If the entry...

IP Configuration
DHCP Server
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Dependencies Between Features
•It is impossible to configure DHCP server and DHCP client on the system at 
the same time, meaning: if one interface is DHCP client enabled, it is 
impossible to enable DHCP server globally.
•If DHCPv4 Relay is enabled, the device cannot be configured as a DHCP 
server.
Default Settings and Configurations
•The device is not configured as...

IP Configuration
DHCP Server
294 Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version) 
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DHCPv4 Server
To configure the device as a DHCPv4 server:
STEP 1Click IP Configuration > IPv4 Management and Interfaces > DHCP Server > 
Properties to display the Properties page. 
STEP  2Select Enable to configure the device as a DHCP server. 
STEP  3Click Apply. The device immediately begins functioning as a DHCP server. 
However, it does not assign IP addresses to...