I I

Ingress PE

Egress PE

The Ingress PE sets the MPLS EXP bits to 3

A P router can recolor the packet EXP bits become 0

Recoloring at P router: the packet becomes out-of-rate

Figure 12-12 Recoloring a Packet in an MPLS VPN Network for the Uniform Model

Copy must happen for all three models

Copy must only happen for uniform model

Copy must happen for all three models

Copy must only happen for uniform model

Ingress PE

The Ingress PE sets the MPLS EXP bits to 3

Egress PE

A P router can recolor the packet EXP bits become 0

Recoloring at P router: the packet becomes out-of-rate

The Uniform model needs extra configuration on the egress PE. The EXP bits of the top label of the received packet must be propagated to the IP precedence or DSCP bits. You can accomplish this by configuring qos-group on the egress PE.

Table 12-4 shows an overview of the three Tunneling models regarding the label operation for plain IP-over-MPLS, MPLS traffic engineering, and MPLS VPN. Consider these three cases:

■ IP-to-Label—The packet is received as an IP packet and forwarded labeled (ingress PE).

■ Label-to-Label—The packet is received labeled and forwarded labeled (P router).

■ Label-to-IP—The packet is received labeled and forwarded as an IP packet (egress PE).

Table 12-4 Overview of the Three Tunneling Models for Plain IP-over-MPLS, MPLS Traffic Engineering, and MPLS VPN

Tunneling Model

IP-to-Label

Label-to-Label

Label-to-IP

Uniform

Copy IP precedence/ DiffServ to MPLS EXP

MPLS EXP copied

Copy MPLS EXP to IP precedence/DiffServ

Pipe

MPLS EXP set according to service provider policy

MPLS EXP copied

Preserve IP precedence/DiffServ

Forwarding treatment based on MPLS EXP

Short Pipe

MPLS EXP set according to service provider policy

MPLS EXP copied

Preserve IP precedence/DiffServ

Forwarding treatment based on IP precedence/DiffServ

With plain IP-over-MPLS, MPLS traffic engineering, and MPLS VPN, the incoming packet is an IP packet. However, in the case of Carrier's Carrier (CsC) and Inter-Autonomous MPLS VPN, the incoming packet on the ingress LSR is already labeled. Then both the Tunneled and the LSP DiffServ information are MPLS EXP bits, but in different labels in the label stack. Thus, it is possible to have hierarchical levels of MPLS DiffServ tunnels.

MQC Commands for MPLS QoS

Cisco IOS lets you change the EXP bits to a new value or implement the behavior of copying the EXP bits to the exposed IP precedence/DSCP bits on the egress LSR. In Cisco IOS, you can use the Modular QoS Command Line Interface (MQC) or Committed Access Rate (CAR) for this. However, MQC is the newest implemented feature and the one with the most capabilities, so it is the only one mentioned here.

You can use two commands in MQC to change the EXP bits of labels. The following command sets the EXP bits in the topmost label:

set mpls experimental topmost value

You can use it in an input or an output service policy.

The next command sets the EXP bits in the pushed label(s):

set mpls experimental imposition value

You can use it only in an input service policy. The value for both commands is between 0 and 7.

To make the impact of these two commands easier to understand, Figures 12-13 through 12-17 show you the result of these commands when you apply them to the input or output interface of a router. The LSP is left to right, so the input interface is the left interface and the output interface is the right interface. The examples demonstrate the impact of the commands in terms of imposition, swapping labels, or disposition of labels. Pay close attention to when the EXP bits of a certain label change.

Figure 12-13 Set MPLS Experimental Commands with Imposition

DSCP=5

EXP =

4

EXP =

3

DSCP

DSCP=5

Remember MPLS QoS Rule 2 for the imposition case. Figure 12-14 Set MPLS Experimental Commands When Swapping Labels

Set MPLS Experimental Topmost 4

Set MPLS Experimental Topmost 4

DSCP=5

Swap

Set MPLS Experimental Topmost 4

NO CHANC

Set MPLS Experimental Imposition 4

Set MPLS Experimental Imposition 4

Set MPLS Experimental Imposition 4

Remember MPLS QoS Rule 2 for the swap case. Figure 12-15 Set MPLS Experimental Commands with Disposition

NO CHANGE!

Disposition

Set MPLS Experimental Topmost 4

DSCP=5

Disposition

Set MPLS Experimental Topmost 4

Disposition Set MPLS Experimental Imposition 4

Disposition Set MPLS Experimental Imposition 4

Remember MPLS QoS Rule 3 in the case of pop.

Figure 12-16 shows an interesting use of the set MPLS experimental commands. You can use the commands on the incoming and outgoing interface at the same time. The top illustration shows you that this gives you an interesting possibility—namely, to recolor the EXP bits of the two labels to a different value. The incoming EXP bits are changed to four by the MQC command on the swapped and pushed labels is on the input interface, and the EXP bits are changed to five only on the top label on the output interface. The bottom illustration in Figure 12-16 is not a very useful one, because you can change the EXP bits by one command on the input or output interface. You do not need to have both commands here, except to show what happens if you do configure both. Clearly, the command on the input or the output interface suffices.

Figure 12-16 Set MPLS Experimental Commands on Input and Output Interfaces

Imposition Set MPLS Experimental Topmost 4

Set MPLS Experimental Topmost 5

Set MPLS Experimental Topmost 5

Set MPLS Experimental Topmost 5

Swapping Set MPLS Experimental Topmost 4

Set MPLS Experimental Topmost 5

Figure 12-17 shows the commands in the case of IP-to-Label imposition.

Figure 12-17 Set MPLS Experimental Commands with IP-to-Label Imposition

EXP =

5

EXP =

5

DSCP

EXP =

4

EXP =

5

DSCP

DSCP=5

Set MPLS Experimental Topmost 4 Set MPLS Experimental Topmost 4

Set MPLS Experimental Topmost 4 Set MPLS Experimental Topmost 4

IP-to-Label Imposition

Set MPLS Experimental Imposition 4

IP-to-Label Imposition Set MPLS Experimental Imposition 4

Remember MPLS QoS Rule 1 for the IP-to-Label case.

Micro Expression Master

Micro Expression Master

If You Could Read Everyone Life A Book You Can Have Better Career, Great Relationships And Become Successful. This Book Is One Of The Most Valuable Resources In The World When It Comes To Reading the smallest and tiniest body Language and know what people are thinking about.

Get My Free Ebook


Post a comment