Leverage SR-TE to Steer VPN Traffic¶

Preparing The Lab¶

Log into the LabAccess jumpserver:
1. Type labs, or select Option 97 to get to the Additional Labs menu.
2. Type or select the option for mesh-topology-evpn-labs in order to get to the EVPN labs.
3. Type srte in this menu to configure the topology with the necessary prerequisites.

Lab Tasks¶

In the first scenario, we will use Segment Routing Traffic Engineering, or SR-TE to manipulate L3VPN traffic for Customer-1. Configure the Service Provider network so that traffic from EOS15 to EOS12 follows the path pictured above.
1. Before beginning the Service Provider configuration, verify connectivity and path to EOS12 on EOS15.
```
ping 12.12.12.12 source 15.15.15.15
traceroute 12.12.12.12 source 15.15.15.15
```
2. To start the configuration, first, create a Prefix-List and Route-Map on EOS1 and EOS6 to set the BGP Color community on the route for EOS12 to a value of 12. Ensure that this is applied to the Customer-1 CE Peering and that there is a open permit at the end to allow other routes that will not be colored.
  
  Note
  
  The BGP Color community is used to identify routes on the ingress PE that should be steered by the SR-TE policy, which we will see in a later step. Since the route for EOS12, 12.12.12.12/32 is received by both PEs, we can set the policy on both.
  
  EOS1
```
ip prefix-list CUSTOMER-1_EOS12 seq 10 permit 12.12.12.12/32
!
route-map CUSTOMER-1_IN permit 10
    match ip address prefix-list CUSTOMER-1_EOS12
    set extcommunity color 12 additive
!
route-map CUSTOMER-1_IN permit 20
!
router bgp 100
    !
    vrf CUSTOMER-1
        neighbor 10.1.11.11 route-map CUSTOMER-1_IN in
```
  EOS6
```
ip prefix-list CUSTOMER-1_EOS12 seq 10 permit 12.12.12.12/32
!
route-map CUSTOMER-1_IN permit 10
    match ip address prefix-list CUSTOMER-1_EOS12
    set extcommunity color 12 additive
!
route-map CUSTOMER-1_IN permit 20
!
router bgp 100
    !
    vrf CUSTOMER-1
        neighbor 10.6.13.13 route-map CUSTOMER-1_IN in
```
3. Next, enable SR-TE on EOS8 and apply the base settings to allow SR-TE tunnels to resolve and set a router-id.
  
  Note
  
  When enabling SR-TE, we must tell the router to look in system-colored-tunnel-rib in order to properly resolve SR-TE tunnels as BGP next-hops.
```
router traffic-engineering
    segment-routing
        rib system-colored-tunnel-rib
    router-id ipv4 8.8.8.8
```
4. With SR-TE enabled, create two static policies on EOS8 that will steer VPN traffic to EOS12 along the desired path to EOS1 and EOS6 for routes with the color value of 12.
  
  Note
  
  With a simple SR-TE static policy, the entire transport label stack is built and applied on ingress to the Service Provider network by the PE. This policy will match the BGP color applied to the VPN route in the previous step. SR-TE policies are defined by endpoint and color so we create one for each egress PE.
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 1.1.1.1 color 12
            description STEER TRAFFIC TO EOS12
        !
        policy endpoint 6.6.6.6 color 12
            description STEER TRAFFIC TO EOS12
```
5. Define a Binding Segment-ID for each policy from the allowed range.
  
  Info
  
  The binding-sid is a required value in order for a policy to be valid. However, it is most commonly used in inter-domain or controller based SR-TE deployments. For this lab, the value isn’t significant.
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 1.1.1.1 color 12
            binding-sid 1000112
        !
        policy endpoint 6.6.6.6 color 12
            binding-sid 1000612
```
6. Define a Path-Group with a preference of 100 for the policies. Within the Path-Group, set the desired MPLS transport label stack to define the path the traffic should take.
  
  Note
  
  In this case, we will explicitly define the MPLS label for each EOS node in the desired path in order. Recall that the MPLS label value is determined by taking the Node SID index value plus the base value of the IS-IS SR label range, which by default is 900,000.
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 1.1.1.1 color 12
            !
            path-group preference 100
                segment-list label-stack 900004 900003 900007 900001
        !
        policy endpoint 6.6.6.6 color 12
            !
            path-group preference 100
                segment-list label-stack 900004 900003 900007 900001 900006
```
7. With the policy fully in place, validate that the policies are active as well as the resolved path on EOS8.
  
  Note
  
  The command will show the policy as active if all attributes are configured correctly. Notice that the Label Stack and the Resolved Label Stack differ slightly. This is due to the fact that EOS will intelligently resolve the path and remove any unnecessary labels in the stack that will still achieve the same path. Also notice that a Backup Resolved Label Stack is calculated because TI-LFA is enabled. In this case, the backup path is somewhat ridiculous as it passes through or close to the egress PE before going back to the initial path. This would be better addressed by creating a secondary path-group with a lower preference.
```
show traffic-engineering segment-routing policy
```
8. Verify the forwarding plane information for EOS12 in the Customer-1 VRF.
  
  Note
  
  Note that the traffic is still ECMP load-balanced since 12.12.12.12/32 is originated from two PEs.
```
show ip route vrf CUSTOMER-1 12.12.12.12
show tunnel fib traffic-engineering segment-routing policy
```
9. Finally, verify connectivity and path again to EOS12 on EOS15.
  
  Note
  
  Note that the additional hops will show in the traceroute path but will not resolve as they are tunneled through on the Service Provider network.
```
ping 12.12.12.12 source 15.15.15.15
traceroute 12.12.12.12 source 15.15.15.15
```
In the next scenario, we will use SR-TE to steer L2VPN traffic for Customer-2. Configure the Service Provider network so that traffic from EOS9 to EOS10 follows the path pictured above.
1. Similar to the L3VPN steering above, steering L2VPN traffic requires setting the BGP Color community. Create a Community-List and Route-Map to match the necessary RT value for Customer-2 which sets the color value to 10 and apply that to the BGP EVPN peering to the Route-Reflector on EOS3 and EOS4.
  
  Note
  
  In this example, we will instead set the color on the ingress PEs attached to the source EOS9. Since this is a EVPN A-A attached CE, we will set the policy on both. Also note that we are using a Community-List to match the RT value instead of the specific CE endpoint.
```
ip extcommunity-list CUSTOMER-2 permit rt 2:20
!
route-map EVPN-COLORING permit 10
    match extcommunity CUSTOMER-2
    set extcommunity color 10 additive
!
route-map EVPN-COLORING permit 20
!
router bgp 100
    !
    address-family evpn
        neighbor 5.5.5.5 route-map EVPN-COLORING in
```
2. Next, enable SR-TE on EOS3 and EOS4 and apply the base settings to for SR-TE. In addition, create the policy for steering traffic to EOS7 with a color of 10 that was set above and set the binding-sid to a value of 1000710.
  
  Abstract
  
  The SR-TE policy config for all VPN types follows the same template.
  
  EOS3
```
router traffic-engineering
    segment-routing
        rib system-colored-tunnel-rib
        !
        policy endpoint 7.7.7.7 color 10
            binding-sid 1000710
            description STEER TRAFFIC TO EOS10
    router-id ipv4 3.3.3.3
```
  EOS4
```
router traffic-engineering
    segment-routing
        rib system-colored-tunnel-rib
        !
        policy endpoint 7.7.7.7 color 10
            binding-sid 1000710
            description STEER TRAFFIC TO EOS10
    router-id ipv4 4.4.4.4
```
3. Finally, define the Path-Group and label stack for the pictured path on EOS3 and EOS4.
  
  Note
  
  Here, we can more intelligently define the label stack necessary to steer traffic along the desired path. By understanding that IS-IS SR will automatically take the shortest path to a given destination router based on the label on the top of the stack, we can skip statically defining the labels for certain intermediate nodes.
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 7.7.7.7 color 10
            !
            path-group preference 100
                segment-list label-stack 900008 900001 900007
```
4. With the policy fully in place, validate that the policies are active as well as the resolved path on EOS3 and EOS4.
```
show traffic-engineering segment-routing policy
```
5. Verify the forwarding plane information for EOS3 and EOS4 in the Customer-2 L2VPN.
  
  Note
  
  The commands below reference the MAC of EOS10, which may differ in your lab. You can find the MAC of EOS10 with the output of show interface Ethernet1.
```
show l2rib output mac 1426.0c23.74e4
show tunnel fib traffic-engineering segment-routing policy
```
6. Finally, verify connectivity to EOS10 on EOS9.
  
  Info
  
  Since the Service Provider is emulating a LAN service, traceroute would not provide additional path hints.
```
ping 10.10.10.10 source 9.9.9.9
```
In the last scenario, we will use SR-TE to steer VPWS traffic for Customer-3. Configure the Service Provider network so that traffic between EOS16 and EOS17 follows the path pictured above bidirectionally.
1. Similar to the L2VPN steering above, steering VPWS traffic requires setting the BGP Color community. Create a Community-List and Route-Map to match the necessary RT value for Customer-2 which sets the color value to 1617 and apply that to the BGP EVPN peering to the Route-Reflector on EOS1 and EOS4.
  
  Info
  
  Since we already created a Route-Map and applied it on EOS4 we will simply add another sequence to that existing Route-Map.
```
ip extcommunity-list CUSTOMER-3 permit rt 3:1617
!
route-map EVPN-COLORING permit 15
    match extcommunity CUSTOMER-3
    set extcommunity color 1617 additive
!
route-map EVPN-COLORING permit 20
!
router bgp 100
    !
    address-family evpn
        neighbor 5.5.5.5 route-map EVPN-COLORING in
```
2. Next, enable SR-TE on EOS1 and apply the base settings to for SR-TE. In addition, create the policy on EOS1 and EOS4 for steering traffic with a color of 1617 (which was set above) and set the binding-sid to a value of 1001617 between EOS1 and EOS4.
  
  Note
  
  Again, SR-TE was already enabled on EOS4 so the base settings are already in place.
  
  EOS1
```
router traffic-engineering
    segment-routing
        rib system-colored-tunnel-rib
        !
        policy endpoint 4.4.4.4 color 1617
            binding-sid 1001617
            description STEER TRAFFIC TO EOS16
    router-id ipv4 1.1.1.1
```
  EOS4
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 1.1.1.1 color 1617
            binding-sid 1001617
            description STEER TRAFFIC TO EOS17
```
3. Finally, define the Path-Group and label stack for the pictured path on EOS1 and EOS4.
  
  Note
  
  Note that the label stacks defined are providing a symmetrical path per the desired TE policy.
  
  EOS1
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 4.4.4.4 color 1617
            !
            path-group preference 100
                segment-list label-stack 900007 900004
```
  EOS4
```
router traffic-engineering
    segment-routing
        !
        policy endpoint 1.1.1.1 color 1617
            !
            path-group preference 100
                segment-list label-stack 900007 900001
```
4. With the policy fully in place, validate that the policies are active as well as the resolved path on EOS1 and EOS4.
```
show traffic-engineering segment-routing policy | section 1617
```
5. Verify the forwarding plane information for EOS1 and EOS4 in the Customer-3 E-LINE Service.
  
  Note
  
  Note that the patch panel configuration is now forwarding into the SR-TE Policy Tunnel.
```
show patch panel forwarding
show tunnel fib traffic-engineering segment-routing policy
```
  Info
  
  Due to a limitation in software forwarding in vEOS-lab, forwarding of VPWS traffic into SR-TE tunnels does not function and as such, we cannot verify functionality via ICMP, etc. All control-plane functions should be verified using the commands above. Steering of VPWS traffic in hardware platforms functions as expected.

Success

Lab Complete!