QoS enables tunneling to be transparent from one edge of a network to the other edge of the network. A tunnel starts where there is label imposition and ends where the label is disposed off. Label disposition is where the label is removed from the stack. The removed packet goes out as an MPLS packet with a different per-hop behavior (PHB) layer underneath or as an IP packet with the IP PHB layer.

Packets are forwarded in the following three ways through a network with respect to QoS.

• Uniform Tunneling Mode In the Uniform Tunneling mode, packets are treated uniformly in the IP and MPLS networks, that is, the IP Precedence value and the MPLS EXP bits always are identical. Whenever a router changes or recolors the PHB of a packet, that change must be propagated to all encapsulation markings. The propagation is performed by a router only when a PHB is added or exposed due to label imposition or disposition on any router in the packet’s path. The color must be reflected everywhere, at all levels.

• Pipe Tunneling Mode

• Short Pipe Tunneling Mode

Pipe mode and Short Pipe mode provide QoS transparency. With QoS transparency, the customer’s IP marking in the IP packet is preserved.

Note	QoS transparency does not support short Pipe mode in this release.

Uniform mode is the default Tunneling Mode available on NCS4K. In this mode, the DiffServ Code Point/MPLS Experimental (EXP) bits as the packet travels from one customer edge (CE) router to another CE router across the MPLS core is as follows:

To implement the pipe tunneling mode, Conditional marking of MPLS experimental bits and DSCP preservation for L3VPN Traffic are enabled.

Conditional Marking of MPLS experimental bits for L3VPN Traffic

The conditional marking of MPLS experimental bits is achieved for Layer 3 VPN traffic by applying a combination of ingress and egress policy maps on the provider edge (PE) router. In the ingress policy map, the QoS-group or discard class is set either based on the result of the policing action or implicitly. The egress policy map matches on qos-group or discard-class and sets the MPLS experiment bits to the corresponding value.

Conditional marking of the MPLS experimental bits is done differently for in-contract and out-of-contract packets. In-contract packets are the confirmed packets with the color green and discard-class set to 0. Out-of-contract packets have exceeded the limit and have the color yellow and discard class set to 1.

Conditional marking of MPLS experimental bits for L3VPN can be done on physical and bundle main interfaces and subinterfaces.

The DSCP value of the IP packet is preserved for L3VPN networks when the experimental remarking is done on the imposition node. The original IP DSCP value is preserved on the disposition node, and egress queuing is done based on MPLS EXP.

Tunneling Pipe Mode

Tunneling Pipe Mode uses two layers of QoS:

• An underlying QoS for the data, which remains unchanged when traversing the core.

• A per-core QoS, which is separate from that of the underlying IP packets. This per-core QoS pre-hop behavior(PHB) remains transparent to end users.

When a packet reaches the edge of the MPLS core, the egress PE router (PE2) classifies the newly exposed IP packets for outbound queuing based on the MPLS PHB from the EXP bits of the recently removed label.

Additional capabilities across Imposition-PE, Core-P, and Disposition-PE nodes are enabled to enable the Functional requirements of Uniform and Pipe tunneling mode.

Imposition-PE

Following Capabilities are enabled in Imposition-PE:

• Supports implicit copy of precedence or DSCP to experimental bits (default mode)

• Supports explicit marking of experimental bits on ingress or egress

• Supports condition experimental bits marking on egress

• Classification based on L4 protocol

Core-P

Following Capabilities are enabled in Core-P:

• Supports no experimental bits remarking (default mode)

• Set MPLS top most at ingress

Disposition-PE

Following Capabilities are enabled in Disposition-PE:

• Experimental bits not copied to DSCP (Default mode)

• Classification on experimental bits in ingress for egress queuing support (pipe mode)

The following is a sample configuration of no experimental bits marking at ingress.

1.Configs at PE-1 (no EXP marking, dscp copied to EXP at imposition) 
a.Ingress policy:
class-map prec3
    match precedence 3
end-class-map

policy-map ingressPE1
    class prec3
      set traffic-class 3
end-policy-map

b.Egress policy:
class-map tc3
   match traffic-class 3
end-class-map

policy-map egressPE1
   class tc3
      shape average percent 10
end-policy-map

2.Configs at P (swapping the label)
a.Ingress policy
class-map mpls-in-exp3
  match mpls experimental topmost 3
end-class-map
    
policy-map mpls-in-pol
  class mpls-in-exp3
   set mpls experimental topmost 2
end-policy-map

3.Configs at PE 2 (EXP not copied to dscp of exposed IP packet)
a.Ingress policy
class-map mpls-in-exp2
    match mpls experimental topmost 2
end-class-map

policy-map ing-PE2
   class mpls-in-exp2
     set traffic-class 2
end-policy-map

b.Egress policy
class-map tc2
match traffic-class 2
end-policy-map

policy-map egr-PE2
   class tc2
     shape average percent 10
end-policy-map

The following is a sample configuration of experimental bits marking at ingress.

1.Configs at PE-1 (setting the EXP label - imposition) 
a.Ingress policy:
class-map dscpcs3
    match dscp cs3
end-class-map

policy-map ingressPE1
    class dscpcs3
      set qos-group 2
end-policy-map

b.Egress policy:
class-map qgrp2
   match qos-group 2
end-class-map

policy-map egressPE1
   class-map qgrp2
      set mpls experimental imposition 4
end-policy-map

2.Configs at P (swapping the label)
a.Ingress policy

class-map mpls-in-exp4
  match mpls experimental topmost 4
end-class-map

policy-map mpls-in-pol-P1
  class mpls-in-exp4
   set mpls experimental topmost 5
 end-policy-map

3.Configs at PE 2 (outgoing queueing policy)
a.Ingress policy
class-map mpls-in-exp5
    match mpls experimental topmost 5
end-class-map

policy-map ing-PE2
   class mpls-in-exp5
     set traffic-class 3
end-policy-map

b.Egress policy

class-map tc3
   match traffic-class 3
end-class-map

policy-map egr-PE2
   class tc3
     shape average percent 10
end-policy-map

The following is a sample configuration of conditional experimental bits marking at ingress.

1.Configs at PE-1 (conditional EXP marking at egress) 
a.Ingress policy:
class-map dscpcs3
    match dscp cs3
end-class-map

policy-map ing-PE1
    class dscpcs3
      set qos-group 2
set traffic-class 2
police rate percent 5 peak-rate percent 10
end-policy-map

b.Egress policy:

class-map match-all qgrp2dc1
   match qos-group 2
   match discard-class 1
end-class-map

class-map match-all qgrp2dc0
  match qos-group 2 
  match discard-class 0 
end-class-map

class-map tc2
  match traffic-class 2
end-class-map

policy-map egr-mark-PE1
   class qgrp2dc1
      set mpls experimental imposition 4
   class qgrp2dc0
      set mpls experimental imposition 6
end-policy-map

policy-map egr-shape-PE1
  class tc2
     shape average percent 5
end-policy-map


2.Configs at P (swapping the label)
a.Ingress policy

class-map mpls-in-exp4
  match mpls experimental topmost 4
end-class-map

policy-map mpls-in-pol-P1
  class mpls-in-exp4
   set mpls experimental topmost 5
 end-policy-map

3.Configs at PE 2 (outgoing queueing policy)
a.Ingress policy

class-map mpls-in-exp5
    match mpls experimental topmost 5
end-class-map

class-map mpls-in-exp6
    match mpls experimental topmost 6
end-class-map

policy-map ing-PE2
   class mpls-in-exp5
     set traffic-class 3
   class mpls-in-exp6
     set traffic-class 4
end-policy-map

b.Egress policy:
class-map tc3
   match traffic-class 3
end-class-map

class-map tc4
   match traffic-class 4
end-class-map

policy-map egr-PE2
   class tc3
     shape average percent 10
   class tc4
     shape average percent 5
end-policy-map

Configuration and Software Restrictions

• In the ingress policy map, if qos-group is set for the incoming traffic packets, then the setting of DSCP and MPLS experimental bits will not work. In other words, set experimental bits/DSCP and set QoS-group cannot be used together. Setting MPLS experimental bits, precedence or DSCP, and QoS-group in the same class on ingress, the result is unpredictable on egress when used for the match.

• Both the ingress and egress policy maps must be applied to attain the expected behavior. If either one of them is not applied, then it might lead to undefined behavior.

• When access control list and QoS co-exist on an interface, the QoS statistics don’t work, whereas the ACL stats always works. When the ACL is removed from the interface, QoS statistics start working.

• All the control traffic hits Class Traffic 6 by default due to the DNX design, we cannot change the queuing.