Enterasys Networks Security Router X-PeditionTM - Manual (Page 297)

QoS with VLAN
XSR User’s Guide 12-15
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
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.
1
2
3
Incoming VLAN tagged frame
F1.1
VLAN 1200
IP 1.2.3.4/24
Ethernet VLAN Tag IP: 9.9.9.1
Priority CFI VLAN: 1200
IP 2.2.3.4/24
F2.1
IP Routing Table
1.2.3.0/24 F1.1
3.3.3.0/24 F2.2
9.9.9.0/24 F2.1 (Static)
Outgoing VLAN tagged frame
Ethernet VLAN Tag IP: 9.9.9.1
2.2.3.0/24 F2.1
F2.2
VLAN 1400
IP 3.2.3.4/24
VLAN 1300
Priority CFI VLAN: 1300
Class Map: matchCos5To7
match cos 5 6 7
Policy Map: setCos4
class matchCos5To7
set cos 4
FastEthernet 2.1
service-policy output setCos4