IP Configuration
Overview
255 Cisco Small Business 300 Series Managed Switch Administration Guide
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Layer 2 IP Addressing
In Layer 2 system mode, the device has up to one IPv4 address and up to two IPv6
interfaces (either “native” interface or Tunnel) 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 Layer2 system mode are configured on
the IPv4 Interface and IPv6 Interfaces pages. In Layer 2 system mode, the device
uses the default gateway, if configured, to communicate with devices that are not
in the same IP subnet with the device. By default, VLAN 1 is the management
VLAN, but this can be modified. When operating in Layer 2 system mode, the
device can only be reached at the configured IP address through its management
VLAN.
The factory default setting of the IPv4 address configuration is DHCPv4. This
means that the device acts as a DHCPv4 client, and sends out a DHCPv4 request
during boot up.
If the device receives a DHCPv4 response from the DHCPv4 server with an IPv4
address, it sends Address Resolution Protocol (ARP) packets to confirm that the IP
address is unique. If the ARP response shows that the IPv4 address is in use, the
device sends a DHCPDECLINE message to the offering DHCP server, and sends
another DHCPDISCOVER packet that restarts the process.
If the device does not receive a DHCPv4 response in 60 seconds, it continues to
send DHCPDISCOVER queries, and adopts the default IPv4 address:
192.168.1.254/24.
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 device.
When a VLAN is configured to use dynamic IPv4 addresses, the device issues
DHCPv4 requests until it is assigned an IPv4 address from a DHCPv4 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, all the interface types (ports,
LAGs, and/or VLANs) on the device can be configured with a static or dynamic IP
address.
The IP address assignment rules for the device are as follows:
•When in Layer 2 system mode, u nless the device is co nfigured with a static
IP address, it issues DHCPv4 requests until a response is received from the
DHCP server.
•If the IP address on the device is changed, the device issues gratuitous ARP
packets to the corresponding VLAN to check IP address collisions. This rule
also applies when the device reverts to the default IP address.