Cisco ASR 9910 - MPLS QoS

[JohnTylerPearce]

Hello,

 Let's say you have specific DSCP AF values that are set for QoS classes. So, if voice if marked at DSCP EF within the ToS byte in the IPv4 Header, makes it way to the PE (within a L3 MPLS VPN environment) PE-CE Link. So, it hits the PE as an IP packet, from that point, does it automatically map the DSCP EF value to a MPLS EXP bit value? I was just curious about this. I've tried to find documentation but have had a hard time locating a document.

[Yahia CHARIF · Accepted solution]

Hi John,

The default behavior on a PE is to map the IP Precedence onto the EXP bits. if using DSCP only the first 3 bits are used since the exp bits field is 3 bit long. Also, when an already labeled packet is imposed with further labels, the EXP bits at ingress side are copied to the imposed labels at egress side.

The default DSCP to MPLS EXP mapping is as follows:

0-7 to 0

8-15 to 1

16-23 to 2

24-31 to 3

32-39 to 4

40-47 to 5

48-55 to 6

56-63 to 7

Hope that will help you.

Best regards.

[JohnTylerPearce]

Thank you very much, I appreciate it.