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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 13 Configuring Interface Characteristics
Interface Types
(6300 mW). The switch provides power to the connected devices on the port if the device needs up to
6.3 W. If the CDP-power negotiated value or the IEEE classification value exceeds the configured cutoff
value, the switch does not provide power to the connected device. After the switch turns on power on the
PoE port, the switch does not police the real-time power consumption of the device, and the device can
consume more power than the maximum allocated amount, which could adversely affect the switch and
the devices connected to the other PoE ports.
Because a standalone switch supports internal power supplies, the total amount of power available for
the powered devices varies depending on the power supply configuration.
• If a power supply is removed and replaced by a new power supply with less power and the switch
does not have enough power for the powered devices, the switch denies power to the PoE ports in
auto mode in descending order of the port numbers. If the switch still does not have enough power,
the switch then denies power to the PoE ports in static mode in descending order of the port numbers.
• If the new power supply supports more power than the previous one and the switch now has more
power available, the switch grants power to the PoE ports in static mode in ascending order of the
port numbers. If it still has power available, the switch then grants power to the PoE ports in auto
mode in ascending order of the port numbers.
The Catalyst 3750-X stackable switch also supports StackPower, which allows power supplies to share
the load across multiple systems in a stack by connecting the switches with power stack cables. You can
collectively manage the power supplies of up to four stack members as a one large power supply For
more information about StackPower, see Chapter 9, “Configuring Catalyst 3750-X StackPower.”
Connecting Interfaces
Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs
cannot exchange data without going through a routing device. With a standard Layer 2 switch, ports in
different VLANs have to exchange information through a router. By using the switch with routing
enabled, when you configure both VLAN 20 and VLAN 30 with an SVI to which an IP address is
assigned, packets can be sent from Host A to Host B directly through the switch with no need for an
external router (Figure 13-1).
Figure 13-1 Connecting VLANs with the 3750-X or 3560-X Switch
When the IP services feature set is running on the switch or the stack master, the switch uses two
methods to forward traffic between interfaces: routing and fallback bridging. If the IP base feature set is
on the switch or the stack master, only basic routing (static routing and RIP) is supported. Whenever
Host A
SVI 1172.20.128.1 172.20.129.1SVI 2
Layer 3 switch
with routing enabled
VLAN 20
Host B
VLAN 30
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