Cisco 500 series Administration Manual page 276

Configuring IP Information
Management and IP Interfaces
NOTE
Cisco 500 Series Stackable Managed Switch Administration Guide
• In Layer 3 system mode on Sx500 devices only, the switch does not
support MAC-based VLAN, Dynamic VLAN Assignment, VLAN Rate Limit,
SYN Rate DoS Protection, and Advanced QoS Policers.
For Sx500 devices only, to configure the system mode (Layer 2 or Layer 3), see the
System Mode and Stack Managemen
Switching from one system mode (layer) to another (in those devices in which it is
supported) requires a mandatory reboot, and the startup configuration of the
switch is then deleted.
Layer 2 IP Addressing
In Layer 2 system mode, the switch has a single IP address in the management
VLAN. This IP address and the default gateway can be configured manually, or by
DHCP. The static IP address and default gateway for Layer 2 system mode are
configured on the IPv4 Interface page. In Layer 2 system mode, the switch uses
the default gateway, if configured, to communicate with devices that are not in the
same IP subnet with the switch. By default, VLAN 1 is the management VLAN, but
this can be modified. When operating in Layer 2 system mode, the switch can only
be reached at the configured IP address through its management VLAN.
The factory default setting of the IP address configuration is DHCP. This means
that the switch acts as a DHCP client, and sends out a DHCP request during boot
up.
If the switch receives a DHCP response from the DHCP server with an IP address,
it sends Address Resolution Protocol (ARP) packets to confirm that the IP address
is unique. If the ARP response shows that the IP address is in use, the switch sends
a DHCPDECLINE message to the offering DHCP server, and sends another
DHCPDISCOVER packet that restarts the process.
If the switch does not receive a DHCP response in 60 seconds, it continues to
send DHCPDISCOVER queries, and adopts the default IP address: 192. 1 68. 1 .254/
24.
IP address collisions occur when the same IP address is used in the same IP
subnet by more than one device. Address collisions require administrative actions
on the DHCP server and/or the devices that collide with the switch.
When a VLAN is configured to use dynamic IP addresses, the switch issues DHCP
requests until it is assigned an IP address from a DHCP server. In Layer 2 system
mode, only the management VLAN can be configured with a static or dynamic IP
address. In Layer 3 system mode, up to 32 interfaces (ports, LAGs, and/or VLANs)
on the switch can be configured with a static or dynamic IP address.
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