Enterasys Networks X-PeditionTM manual Describing Vlan QoS Packet Flow

QoS with VLAN

Describing VLAN QoS Packet Flow

The following scenarios illustrate how prioritized VLAN and non-VLAN packets behave across XSR interfaces with VLAN and QoS configured and include minimal CLI commands.

VLAN Packet with Priority Routed out a Fast/GigabitEthernet Interface

The following scenario is illustrated in Figure 12-3.

1.After the XSR accepts a VLAN-tagged Ethernet frame, the tag is stripped and the VLAN ID within the tag is used in the process of mapping the frame to a sub-interface of the Fast/ GigabitEthernet interface. The priority bits are stored internally with the frame.

2.The IP packet in the Ethernet frame is routed according to the XSR’s forwarding table which learns the next hop and outgoing interface.

3.If the outgoing port is associated with a VLAN by a <VLAN ID>, the XSR will create a VLAN tag with the <VLAN ID> and insert it in the outgoing Ethernet frame. Also, if priority bits are stored with the frame, they will be marked in the VLAN tag. Lastly, if QoS is configured on the XSR’s output interface, it will be applied accordingly. In this case, the policy map setCos4 is applied to the output sub-interface FastEthernet 2.1. Since the input priority was 7, it will match the class matchCos5To7. The output VLAN frame will be marked with a priority of 4.

Figure 12-3 VLAN/QoS Ethernet Scenario

IP Routing Table	VLAN 1300
1.2.3.0/24 F1.1
2.2.3.0/24 F2.1	IP 2.2.3.4/24
3.3.3.0/24 F2.2

VLAN 1200	9.9.9.0/24 F2.1 (Static)
IP 1.2.3.4/24	F2.1
		Ethernet	VLAN Tag	IP: 9.9.9.1

Ethernet	VLAN Tag IP: 9.9.9.1		F1.1	F2.2
	1
				VLAN 1400
				IP 3.2.3.4/24
Priority	CFI	VLAN: 1200

Incoming VLAN tagged frame

3

Priority CFI VLAN: 1300

Outgoing VLAN tagged frame

Class Map: matchCos5To7 match cos 5 6 7

Policy Map: setCos4 class matchCos5To7 set cos 4

FastEthernet 2.1 service-policy output setCos4

VLAN Packet with Priority Routed out a Serial Interface

In this scenarios, pictured in Figure 12-4, the policy map setDscp is applied to the output interface Serial 1. Since the input priority was 7 it will match the class matchCos5To7. The IP packet will be marked with a DSCP of 46.

XSR User’s Guide 12-15