Cisco Cisco 2504 Wireless Controller 기술 매뉴얼
CoS and DSCP Switch Operation
Differentiated Services Code Point (DSCP) is a tag in layer 3 of the IP header, so it always survives
throughout the journey of the packet. DSCP contains a hex/decimal value but is usually translated into a
friendly name.
throughout the journey of the packet. DSCP contains a hex/decimal value but is usually translated into a
friendly name.
For example, a voice packet is usually tagged Expedited Forwarding (EF), which has a decimal value of 46.
This table gives the correspondance:
This table gives the correspondance:
DSCP Name Binary Decimal IP Precedence
CS0
000 000 0
0
CS1
001 000 8
1
AF11
001 010 10
1
AF12
001 100 12
1
AF13
001 110 14
1
CS2
010 000 16
2
AF21
010 010 18
2
AF22
010 100 20
2
AF23
010 110 22
2
CS3
011 000 24
3
AF31
011 010 26
3
AF32
011 100 28
3
AF33
011 110 30
3
CS4
100 000 32
4
AF41
100 010 34
4
AF42
100 100 36
4
AF43
100 110 38
4
CS5
101 000 40
5
EF
101 110 46
5
CS6
110 000 48
6
CS7
111 000 56
7
Call signaling is often tagged as CS3, while voice is EF. You usually need to remember the friendly names
rather than the actual values.
rather than the actual values.
IP phones or even software applications send voice traffic tagged as EF.
CoS is a layer 2 tag, also called 802.1p, that sits in the 802.1q VLAN tag header; therefore, it is present only
when a VLAN tag is present, such as on trunk ports. For this reason, it is a non-surviving tag that disappears
when the packet is routed to another subnet or when the packet goes through an access port.
when a VLAN tag is present, such as on trunk ports. For this reason, it is a non-surviving tag that disappears
when the packet is routed to another subnet or when the packet goes through an access port.
It is perfectly acceptable for both values to coexist, and they always coexist on trunk ports.
When you enter the mls qos trust dscp command on a port, the switch uses the DSCP value on incoming
packets in order to put the packets in the right queue (internal voice, video, or best effort queue). When the
packet is resent on another port, the switch sets the CoS tag to match the DSCP so there is no conflict between
the two values; if the CoS tag is present, it is a trunk port.
packets in order to put the packets in the right queue (internal voice, video, or best effort queue). When the
packet is resent on another port, the switch sets the CoS tag to match the DSCP so there is no conflict between
the two values; if the CoS tag is present, it is a trunk port.
When you enter the mls qos trust cos command on a port, the switch uses the CoS marking on incoming
packets in order to put the packet in the right queue. When the packet is resent, the switch makes the DSCP
packets in order to put the packet in the right queue. When the packet is resent, the switch makes the DSCP