Juniper Networks EX2500 manual Port-Based Vlan Assignment

Chapter 2: VLANs

Figure 2: Port-Based VLAN Assignment

		PVID = 2
Untagged packet
				4
CRC	Data	SA	DA	Port

Before

Port 1		Port 2	Port 3		Tagged member
					of VLAN 2
				5
	802.1Q Switch			Port
Port 6		Port 7	Port 8

Untagged member of VLAN 2

BS45011A

As shown in Figure 3, the untagged packet is marked (tagged) as it leaves the switch through port 5, which is configured as a tagged member of VLAN 2. The untagged packet remains unchanged as it leaves the switch through port 7, which is configured as an untagged member of VLAN 2.

Figure 3: 802.1Q Tagging (after Port-Based VLAN Assignment)

PVID = 2		Port 1		Port 2	Port 3
	4
	Port		802.1Q Switch
		Port 6		Port 7	Port 8

Untagged memeber	CRC
of VLAN 2
	Data
Outgoing	SA
untagged packet	DA
(unchanged)

Tagged member of VLAN 2

5
Port	CRC*		Data		Tag		SA	DA
(*Recalculated)
				8100		Priority		CFI	VID = 2
				16 bits		3 bits		1 bits	12 bits
							After
		Key
		Priority		- User_priority
		CFI		- Canonical format indicator
		VID		- VLAN identifier

BS45012A

In Figure 4, tagged incoming packets are assigned directly to VLAN 2 because of the tag assignment in the packet. Port 5 is configured as a tagged member of VLAN 2, and port 7 is configured as an untagged member of VLAN 2.

Figure 4: 802.1Q Tag Assignment

Tagged packet

CRC Data Tag

Before

PVID = 2
		4
SA	DA	Port

Port 1		Port 2	Port 3		Tagged member
					of VLAN 2
				5
	802.1Q Switch			Port
Port 6		Port 7	Port 8

Untagged member of VLAN 2

BS45013A

VLAN Tagging „ 25