You can configure AS path and local preference as follows:

The AS path prepend and local preference is route qualifiers like the community. The same process can be followed for AS path prepend and local preference.

The configuration will support setting a local preference value for all the VIP and SNAT routes advertised. This is a field in the BGP profile which is part of VRF.

The configuration supports setting the number of times the local AS is to be prepended in the VIP and SNAT routes advertised. This is a field in the BGP profile which is part of VRF.

Configuring AS Path using NSX Advanced Load Balancer UI

Configuring AS path is supported using NSX Advanced Load Balancer UI.

Navigate to Infrastructure > Routing > BGP Peering and provide the value for the AS-Path Prepend as shown below:





Configuring AS Path using NSX Advanced Load Balancer CLI

The following is the CLI to configure the AS path:

[admin:ctlr1]: > configure vrfcontext global
[admin:ctlr1]: vrfcontext> bgp_profile
[admin:ctlr1]: vrfcontext:bgp_profile> num_as_path_prepend 5
[admin:ctlr1]: vrfcontext:bgp_profile> save
[admin:ctlr1]: vrfcontext> save
+-----------------------+-------------------------------------------------+
| Field                 | Value                                           |
+-----------------------+-------------------------------------------------+
| uuid                  | vrfcontext-4f58cb16-eedb-41d1-a125-538e512f11bb |
| name                  | global                                          |
| bgp_profile           |                                                 |
|   local_as            | 66000                                           |
|   ibgp                | False                                           |
|   keepalive_interval  | 60                                              |
|   hold_time           | 180                                             |
|   send_community      | True                                            |
|   num_as_path_prepend | 5                                               |
|   shutdown            | False                                           |
| system_default        | True                                            |
| lldp_enable           | True                                            |
| tenant_ref            | admin                                           |
| cloud_ref             | Default-Cloud                                   |
+-----------------------+-------------------------------------------------+
Network          Next Hop            Metric LocPrf Weight Path
*>100.64.1.126/32  100.64.1.69              0             0 65000 i
*>100.64.1.153/32  100.64.1.39              0             0 65000 65000 65000 65000 65000 65000 i

As per the above use case, on the upstream router, the AS path has been prepended with N+1, wherein the N=AS path is defined while doing the configuration in the BGP profile.

Configuring Local Preference using NSX Advanced Load Balancer UI

Configuring AS path is supported using NSX Advanced Load Balancer UI.

Navigate to Infrastructure > Routing > BGP Peering and provide the value for the Local Preference as shown below:



Note:

Any configuration change in AS path prepend or local preference parameters can result in a BGP connection to the peers being flapped.

Configuring Local Preference using NSX Advanced Load Balancer CLI

The following is the CLI to configure the local preference:

[admin:ctlr1]: > configure vrfcontext global
[admin:ctlr1]: vrfcontext:bgp_profile> local_preference 500
[admin:ctlr1]: vrfcontext:bgp_profile> save
[admin:ctlr1]: vrfcontext> save
+----------------------+-------------------------------------------------+
| Field            	| Value                                       	|
+----------------------+-------------------------------------------------+
| uuid             	| vrfcontext-b894161d-d517-4f11-ac78-ee869389fe1e |
| name             	| global                                      	|
| bgp_profile      	|                                             	|
|   local_as       	| 6000                                        	|
|   ibgp           	| True                                        	|
|   keepalive_interval | 60                                          	|
|   hold_time      	| 180                                         	|
|   send_community 	| True                                        	|
|   local_preference   | 500                                         	|
|   shutdown       	| False                                       	|
| system_default   	| False                                       	|
| tenant_ref       	| admin                                       	|
| cloud_ref        	| Default-Cloud                               	|
+----------------------+-------------------------------------------------+
Network               Next Hop            Metric LocPrf Weight Path
>i0.0.0.0/0         100.64.2.70             500      0 i
>i10.79.172.0/22    100.64.2.70    0        500      0 i

As per the above use case, on the upstream router, the local preference has been updated to the configured value.

Local AS Override for an iBGP Profile in VRF

This feature is required for cases where the local AS in an iBGP profile on a VRF needs to be decided based on the peers reachable through the SE. For instance, the networks where routers that support only 2-byte AS number and more recent routers co-exist.

When a VRF and its BGP profile is deployed in an SE, if there are peer configurations with ibgp_local_as_override set and the peer subnet applies to the SE, the profile level local_as will be overridden with the peer level remote_as.

The following are a few constraints in the configuration:

  • This feature is only for iBGP networks.

  • If there are multiple peers with subnets to the same TOR in the SE and ibgp_local_as_override is enabled, then all the peers should have the same remote_as value.

Example config

+----------------------------+-------------------------------------------------+
| Field                      | Value                                           |
+----------------------------+-------------------------------------------------+
| uuid                       | vrfcontext-553674bd-44b9-4a22-b4d6-8bf804e0f046 |
| name                       | global                                          |
| bgp_profile                |                                                 |
|   local_as                 | 100                                             |
|   ibgp                     | True                                            |
|   peers[1]                 |                                                 |
|     remote_as              | 200                                             |
|     peer_ip                | 100.64.3.10                                     |
|     subnet                 | 100.64.3.0/24                                   |
|     bfd                    | True                                            |
|     advertise_vip          | True                                            |
|     advertise_snat_ip      | True                                            |
|     advertisement_interval | 5                                               |
|     connect_timer          | 10                                              |
|     ebgp_multihop          | 0                                               |
|     shutdown               | False                                           |
|     ibgp_local_as_override | True                                            |
|   peers[2]                 |                                                 |
|     remote_as              | 200                                             |
|     peer_ip                | 100.64.4.10                                     |
|     subnet                 | 100.64.4.0/24                                   |
|     bfd                    | True                                            |
|     advertise_vip          | True                                            |
|     advertise_snat_ip      | True                                            |
|     advertisement_interval | 5                                               |
|     connect_timer          | 10                                              |
|     ebgp_multihop          | 0                                               |
|     shutdown               | False                                           |
|     ibgp_local_as_override | True                                            |
|   peers[3]                 |                                                 |
|     remote_as              | 300                                             |
|     peer_ip                | 100.64.5.10                                     |
|     subnet                 | 100.64.5.0/24                                   |
|     bfd                    | True                                            |
|     advertise_vip          | True                                            |
|     advertise_snat_ip      | True                                            |
|     advertisement_interval | 5                                               |
|     connect_timer          | 10                                              |
|     ebgp_multihop          | 0                                               |
|     shutdown               | False                                           |
|     ibgp_local_as_override | True                                            |
|   peers[4]                 |                                                 |
|     remote_as              | 100                                             |
|     peer_ip                | 100.64.6.10                                     |
|     subnet                 | 100.64.6.0/24                                   |
|     bfd                    | True                                            |
|     advertise_vip          | True                                            |
|     advertise_snat_ip      | True                                            |
|     advertisement_interval | 5                                               |
|     connect_timer          | 10                                              |
|     ebgp_multihop          | 0                                               |
|     shutdown               | False                                           |
|   keepalive_interval       | 60                                              |
|   hold_time                | 180                                             |
|   send_community           | True                                            |
|   shutdown                 | False                                           |
| system_default             | True                                            |
| lldp_enable                | True                                            |
| tenant_ref                 | admin                                           |
| cloud_ref                  | Default-Cloud                                   |
+----------------------------+-------------------------------------------------+

With the above config, the following are the only valid SE peering:

Peering with Peers

Quagga Config Local AS

peering with peers[1]

200

peering with peers[2]

200

peering with peers[1] and [2]

200

peering with peers[3]

300

peering with peers[4]

100

Note:

Any other combination of peering is invalid and result in all the BGP virtual services deployed in the SE with this VRF going to OPER_DOWN state.