7.5.3 Switching communication between member switch

You can configure the stack to switch communications quickly in the event of a member switch failure or recovery. If you need to switch communications in a short period of time, configure link aggregation across multiple member switches to connect to other devices, and then use a function that supports short-time communication switching on the stack. The following table describes the support status of short-time communication switching in the stack by using functionality.

Table 7-6: Short-time communication switching support status on the stack
Category	Functionality	Supported
Network Interfaces	Ethernet	OK
Link Aggregation	Static	OK
	LACP^#1	OK
	Standby link	NG
Layer 2 Switching	MAC Address Learning	OK
	VLAN	OK
	VLAN tunneling	OK
	Tag translation	OK
	Inter-port relay blocking	OK
	Spanning Tree Protocols	NG^#2
	Ring Protocol^#3	OK
	IGMP snooping	OK^{#4 #5}
Filters and QoS	Access lists	OK
Filters and QoS	QoS	OK
Layer 2 Authentication	IEEE 802.1X	OK
	Web Authentication	OK
	MAC-based Authentication	OK
	Multistep authentication	OK
Security	DHCP snooping^#4	OK
High Reliability Based on Redundant Configurations	GSRP aware^#4	OK
High Reliability Based on Redundant Configurations	Uplink redundant36	OK
Network monitoring function	L2 Loop Detection	OK
Network monitoring function	Storm Control	OK
Network management	Port Mirroring	OK
	Policy-Based Mirroring	OK
	IEEE 802.3ah/UDLD	OK

Legend OK: Supported; NG: Not supported

#1

If the following conditions are satisfied, communication can continue without downgrading LACP channel group when the master switch is switched. However, when the master switch is switched, LACPDU is not sent until LACPDU is received from the partner switch even if LACP startup mode of the Switch is active. Therefore, if the partner switch also supports LACP short-time communication switching, if the master switch is switched between the Switch and the partner switch at the same time, both switches enter LACPDU receive wait status and the channel group goes down due to a timeout.

The port-detachment limiting functionality does not operate until LACPDU is received from the partner switch.

Table 7-7: Conditions for continuing communication
Item	Switch	Facing device
Configuring Link Aggregation across Multiple Member Switches	Required	Optional
LACPDU Transmit Interval	long	long

#2

Repeat the topology calculation from the beginning when switching the master switch. Communication of VLAN running Spanning Tree is stopped until the topology calculation is completed.

#3

You can switch communication for a short period of time without having to configure link aggregation across multiple member switches.

#4

For frames forwarded by software, forwarding stops for up to 10 seconds when the master switch is switched. For details about the frames used for software forwarding, see Table 24-8: Functions and frame types used for software forwarding for Layer 2 frame forwarding.

#5

When IGMP snooping is used, Layer 2 forwarding of IPv4 control packets destined for 224.0.0.0/24 is software-processed, and forwarding stops for up to 10 seconds when the master switch is switched. For example, VRRP virtual router passing through the Switch may become a double-master.

For this reason, VRRP must ensure control packet communication by setting the sending interval of ADVERTISEMENT packets to 6 seconds or more.

#6

The following combination of uplink and redundant ports can only be used to restore communication for a short period of time.

.2 physical ports

.Link aggregation in physical ports and single member switches

.2 link aggregations in a single member switch

The communication switching time includes the link down detection time of the line connected to the stack and the link up detection time.