22.3 Coexistence of Layer 2 switch function and other functions

When the Layer 2 switch functionality is used, other functionality might be restricted or disabled. The following table describes the restrictions regarding combinations of functionality.

Note that only functionality with compatibility restrictions is shown in the table.

Table 22-3 Limitations of MAC address learning
Functionality used	Functionality	Restrictions
MAC Address Learning	Uplink Redundancy	Can only be partially used^#

#: Static entries cannot be used for uplink port pairs.

Table 22-4 Limitations on VLANs
Functionality used		Functionality	Restrictions
VLAN type	Port VLAN	VLAN tunneling	Partially limited*1
		Layer 2 Authentication	Partially limited*2
		Port mirroring (mirrored ports)	Partially limited*3
	Protocol VLAN	Default VLAN	Cannot be used
		VLAN tunneling
		PVST+
		Layer 2 Authentication	Partially limited*2
		Port mirroring (mirrored ports)	Cannot be used
	MAC VLAN	Default VLAN	Cannot be used
		VLAN tunneling
		PVST+
		Layer 2 Authentication	Partially limited*2
		Port mirroring (mirrored ports)	Cannot be used
Default VLAN		Protocol VLAN	Cannot be used
		MAC VLAN
		IGMP snooping
		MLD snooping
		Layer 2 Authentication	Partially limited*2
		Port mirroring (mirrored ports)	Partially limited*3
Extended VLAN Functionality	Tag translation	PVST+	Cannot be used
		IGMP snooping
		MLD snooping
		Uplink Redundancy	Partially limited*4
	VLAN tunneling	Port VLAN	Partially limited*1
		Protocol VLAN	Cannot be used
		MAC VLAN
		PVST+
		Single Spanning Tree
		Multiple Spanning Tree
		IGMP snooping
		MLD snooping
		Layer 2 Authentication	Partially limited*2
		DHCP Snooping	Cannot be used
		Uplink Redundancy	Partially limited*4
	L2 Protocol Frame Transparency (BPDU)	PVST+	Cannot be used
		Single Spanning Tree
		MSTP
	L2 Protocol Frame Transparency (EAP)	Layer 2 Authentication	Partially limited*2
	Inter-port relay blocking functionality	IGMP snooping	Partially limited*5
		MLD snooping
		Layer 2 Authentication
		DHCP Snooping
		GSRP aware
		CFM

#1: When using the VLAN tunneling functionality, do not use a native VLAN on a trunk port.
#2: See "Configuration Guide: Using Vol.2" "5.2.1 Layer 2 Authentication with Other Features."
#3: This function is available only when 802.1Q Tag grant function is used.
#4: Cannot be used on an uplink port.
#5: When the limited functionality is enabled, Layer 2 forwarding of some frames becomes software processing. Frames forwarded by software are not subject to inter-port forwarding shutdown. For details about the frames used for software forwarding, see Table 22-8: Functions and frame types used for software forwarding for Layer 2 frame forwarding.

Table 22-5: Restrictions on spanning tree
Functionality used	Functionality	Restrictions
PVST+	Protocol VLAN	Cannot be used
	MAC VLAN
	VLAN tunneling
	Tag translation
	L2 protocol frame transparency functionality (BPDU)
	Multiple Spanning Tree
	Ring Protocol
	Layer 2 Authentication	Can only be partially used^#
	Uplink Redundancy	Cannot be used
Single Spanning Tree	VLAN tunneling	Cannot be used
	L2 protocol frame transparency functionality (BPDU)
	Multiple Spanning Tree
	Ring Protocol
	Layer 2 Authentication	Can only be partially used^#
	Uplink Redundancy	Cannot be used
Multiple Spanning Tree	VLAN tunneling	Cannot be used
	L2 protocol frame transparency functionality (BPDU)
	Single Spanning Tree
	PVST+
	Loop guard
	Ring Protocol
	Layer 2 Authentication	Can only be partially used^#
	Uplink Redundancy	Cannot be used

#: See "Configuration Guide: Using Vol.2" "5.2.1 Layer 2 Authentication with Other Features."

Table 22-6 Restrictions on the Ring Protocol
Functionality used	Functionality	Restrictions
Ring Protocol	PVST+	Cannot be used
	Single Spanning Tree
	Multiple Spanning Tree
	Layer 2 Authentication	Partially limited*1
	Uplink Redundancy	Partially limited*2

#1: See "Configuration Guide: Using Vol.2" "5.2.1 Layer 2 Authentication with Other Features."
#2: Cannot be used with a ring port.

Table 22-7 Restrictions on IGMP snooping/MLD snooping
Functionality used	Functionality	Restrictions
IGMP snooping	Default VLAN	Cannot be used
	Tag translation
	VLAN tunneling
	Inter-port relay blocking functionality	Can only be partially used^#
MLD snooping	Default VLAN	Cannot be used
	Tag translation
	VLAN tunneling
	Inter-port relay blocking functionality	Can only be partially used^#
	Layer 2 Authentication	Cannot be used

#: When IGMP snooping/MLD snooping is enabled, Layer 2 forwarding of some frames is software-processed. Frames forwarded by software are not subject to inter-port forwarding shutdown. For details about the frames used for software forwarding, see Table 22-8: Functions and frame types used for software forwarding for Layer 2 frame forwarding.

Table 22-8: Functionality and type of frames for which Layer 2 frame forwarding is software forwarding
Function that generates software relay		Frame to be used as a software relay
IGMP snooping		IGMP datagram
		PIM protocol-specific Hello messaging
		224.0.0.0 /24 as the destination IPv4
MLD snooping		MLD datagram
MLD snooping		IPv6 addressed to ff02::/16
Layer 2 Authentication	ARP packet relay functionality	ARP packet*
DHCP Snooping	Monitoring DHCP packets	DHCP datagram
DHCP Snooping	Dynamic ARP inspection	ARP packet
GSRP aware		GSRP Flush request frame
CFM		Linktrace messages

#: Only ARP packets sent from pre-authentication terminals are forwarded by software.