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​MPLS QoS - Explicit Null

Picture
On CSR1, we'll create a policy-map that sets the top most label, the LDP label, EXP bits to a value of 3 rather than the received 6 from control plane traffic. We aren't changing the Telnet QoS marking, we're just changing the EXP marking as it traverses the SP backbone.

CSR1
policy-map PM_EXP3_TO_CORE
 class class-default
  set mpls experimental topmost 3
!
interface GigabitEthernet1
 service-policy output PM_EXP3_TO_CORE


CSR1#show policy-map interface g1 output 
 GigabitEthernet1 

  Service-policy output: PM_EXP3_TO_CORE

    Class-map: class-default (match-any)  
      2257 packets, 659347 bytes
      5 minute offered rate 3000 bps, drop rate 0000 bps
      Match: any 
      QoS Set
        mpls experimental topmost 3
          Marker statistics: Disabled
Picture
As you can see in the above output, the EXP marking of 3 did take affect and is visible on CSR3
Picture

On the egress PE, we don't see that marking show up with traffic going from IOS17 to IOS18. In order to affect this, we need to tell CSR3 not to PHP the top or transport label. 

CSR3#show mpls forwarding-table 192.0.2.5 32
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
29         Pop Label  192.0.2.5/32     18962         Gi5        10.3.5.5  


CSR5
mpls ldp explicit-null

CSR3#show mpls forwarding-table 192.0.2.5 32
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
29         explicit-n 192.0.2.5/32     418           Gi5        10.3.5.5    


We can see by adding the explicit null command on CSR5, that the Pop label is now explicit-n.


CSR5#show bgp vpnv4 unicast all 10.101.18.0/24
BGP routing table entry for 100:1:10.101.18.0/24, version 1488
Paths: (1 available, best #1, table C1)
  Advertised to update-groups:
     13        
  Refresh Epoch 1
  65100
    101.5.18.18 (via vrf C1) from 101.5.18.18 (10.101.18.18)
      Origin IGP, metric 0, localpref 100, valid, external, best
      Extended Community: SoO:65100:100 RT:192.0.2.5:1
      mpls labels in/out 45/nolabel
      rx pathid: 0, tx pathid: 0x0


​To verify the labeling, take a look at the BGP VPNv4 table and see that label 45 is applied to the 10.101.18.0/24 network. Which is the VPN label visible in the below output.
Picture
After the explicit null attribute is applied. We see that Label 0 is visible and Explicit Null is used. The Label of 3 is now being used.


​CSR3#show mpls forwarding-table 192.0.2.5 32
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
29         explicit-n 192.0.2.5/32     3712          Gi5        10.3.5.5    
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  • Home
  • Technology VoD!
    • Cisco >
      • Route & Switch / Enterprise Infrastructure
  • Technology Breakdowns!
    • Route&Switch/Ent. Infra. >
      • L2 Technologies
      • L3 Technologies
      • VPN Technologies
      • Services >
        • IOS - Dynamic NAT
        • HSRP - IPv4 Setup
        • HSRP - Priority and Preemption
    • Service Provider >
      • IGPs (Interior Gateway Protocols)
      • First Hop Redundancy >
        • HSRP (Hot Standby Router Protocol) >
          • HSRP - IOS/IOS XE Setup
          • HSRP - IOS XR Setup
      • BGP (Border Gateway Protocol)
      • Inter AS Multicast (MSDP)
      • Intra-AS MPLS
      • Inter-AS MPLS
    • Security >
      • IOS Firewall
      • ASA Firewall
      • FirePOWER Threat Defense >
        • FTD - FTD NGFW Device Setup and FMC Integration
      • VPNs >
        • PKI
        • Site to Site VPNs
        • Remote Access VPNs >
          • IOS Remote Access
          • ASA Remote Access
    • Data Center >
      • Nexus 9000v >
        • Nexus 9000v - Enabling Features
        • Nexus 9000v - VLANs and Trunks
        • Nexus 9000v - LACP Port Channels
        • Nexus 9000v - vPC (Virtual Port Channel)
        • Nexus 9000v - OSPFv2
        • Nexus 9000v - VXLAN - Ingress Replication Flood and Learn
        • Nexus 9000v - IP Multicast
        • Nexus 9000v - VxLAN - Multicast Flood and Learn
        • Nexus 9000v - VxLAN - BGP EVPN with Multicast
        • Nexus 9000v - VxLAN - BGP EVPN w/Ingress Replication
        • Nexus 9000v - VxLAN - Inter-VxLAN Routing with BGP EVPN
        • Nexus 9000v - VXLAN - External Routing
      • Nexus 7000v
    • Palo Alto