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
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
As you can see in the above output, the EXP marking of 3 did take affect and is visible on CSR3
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.
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.
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
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
