NAT Configuration on Avi Service Engine


This guide explains the NAT feature on Avi Service Engine. When new application servers are deployed, the servers need external connectivity for manageability. In the absence of a router in the server networks, the Avi SE can be used for routing the traffic of server networks by using IP routing feature of Service Engines. Also you need NAT functionality in the SE to use a NAT gateway for the entire private network of servers.

Note: This feature is not supported for IPv6.

NAT will function in post-routing phase of packet path in the SE. It is recommended to go through the SE default gateway (IP routing on Service Engine) feature as well. Refer to Default Gateway (IP Routing on Avi SE) for more details.

Enabling IP routing on Service Engine and using the SE as gateway is a necessary prerequisite to use outbound NAT functionality. Hence all necessary requirements for enabling IP routing on Service engine is also applicable to outbound NAT functionality.

Note: Outbound NAT is supported for TCP/UDP, and ICMP flows.

NAT Guidelines

NAT is VRF-aware and must be programmed per SE group via a network service of Routing Service type. Refer to Network Service for more details.

NAT/IP routing is supported on two-armed, no-access configurations of Linux server clouds and (as of Avi Vantage version 18.2.5) VMware clouds.

Starting with Avi Vantage version 18.2.5, Avi Vantage supports NAT for VMware cloud deployments in write access mode. For this feature to work on VMware write access clouds, atleast one virtual service must be configured with the following configurations:

  • One arm (in the two-arm mode deployment) must be placed in the back-end network. For this network, the SE acts as the default gateway.
  • The other arm is placed in the desired front-end network.
  • The SE group of the network service must be in legacy HA (active/standby).
  • The Routing Service should have enabled routing set.
  • NAT functionality is done by Service Engine IP stack, so the routing_by_linux_ipstack attribute of Routing Service should be set to False.
  • Only DPDK-based SEs are allowed.
  • VMware write access mode, if a virtual service has already been created. This virtual service creates the required Service Engines.
  • NAT IP of a NAT Rule cannot be same as any interface IP present in the VRF. Such NAT IP will be ignored.
  • NAT IP is configured on an interface as a secondary IP. Hence different Service Engine groups can not share a NAT IP in a given VRF.

NAT Service

The diagrammatic representation of NAT service traffic initiated from inside to outside is as follows:


The flow details mentioned in the above screenshot is from 1 to 8. The details of the flow are as follows:

Flow Count Description
1 The server ARP's for DG and gets MAC-A. The server sends IP packet to MAC-A. [S:IP-SX, D:IP-Ext]
2 Service Engine creates a NAT entry since this is a new flow, does NAT of src-IP and sport and sends packet to router (MAC-R). [S:SE-NIP, D:IP-Ext]
3 Router uses internet routing to forward to Ext. [S:SE-NIP, D:IP-Ext]
4 Ext receives the packet sent by SX. [S:SE-NIP, D:IP-Ext]
5 Packet received by destination. [S:IP-Ext, D:SE-NIP]
6 Router ARP's for SE-NIP and SE-Active responds to ARP. [S:IP-Ext, D:SE-NIP]
7 SE looks up NAT flow table and based on the match, it changes the dst-IP:port to real server IP port. [S:IP-Ext, D:IP-SX]
8 SE does IP routing and sends packet to MAC-SX. [S:IP-Ext, D:IP-SX]


  • The router acts as front-end floating IP for the SE group. SE backend network is not routable on the front end.
  • In the floating IP, the backend network is not routable on the front end.

NAT requires the following configurations at various points in the network:

  • On the Avi Controller, enable Enable IP Routing in the Service Engine group (only Legacy HA) in Advanced tab configuration.
  • On the front-end router, configure static routes to the back-end server networks with the nexthop as floating IP in front-end network.
  • On the back-end router, configure the SE’s floating IP in back-end server network as the default gateway.

Configuring NAT Policy

Configuring NAT Policy using UI

The following are the steps to configure NAT policy:

  1. Navigate to Template > Policies > NAT Policy. Click CREATE.


  2. Specify the name of the NAT policy.

  3. Check Enable Rule box.

  4. Specify the Destination and Source IP address in the Match tab.

  5. Under the Action tab, select the Type.
    • Dynamic IP and Port helps Source IP NAT with Port-Address Translation for packets originating from the Internal Network. This applies to TCP, UDP, and ICMP protocol packets.
    • Dynamic IP and Preserve Port (supported from NSX Advanced Load Balancer version 22.1.6) helps in preserving the source-port of packet coming from Internal Network. So, this action does only Source NAT of the IP without doing the Port-Address Translation.
      Note: Dynamic IP and Preserve Port is applicable only for matching rules and specifically for UDP traffic.


  6. Click Save after specifying the necessary details.

Configuring NAT Policy using CLI

You can configure NAT policy as follows:

Step 1: Assume is the destination-IP on which server is trying to reach, is the NAT IP. This IP is owned by Service Engine. Note that the NAT IP has to be configured as a static-route on the front-end router with next-hop as front-end floating-interface-ip ( of the SE.

configure natpolicy nat-policy-default-group-global
    rules index 1
        name rule1
              source_ip match_criteria is_in
                    ranges begin end
              destination_ip match_criteria is_in
                    destination_port match_criteria is_in
                         ports 80
                         ports 443
                    source_port match_criteria is_not_in
                         ports 800
         type nat_policy_action_type_dynamic_ip_port

Assume that the Service Engine Group name is set to DefaultGroup with SE-interfaces present in VRF global.

Step 2: Create a NetworkService that has NAT policy.

configure networkservice nat-policy-default-group-global
      vrf_ref global
      se_group_ref Default-Group
      service_type routing_service
            nat_policy_ref nat-policy-default-group-global

Step 3: Configure ServiceEngineGroup in Legacy-HA and EnableRouting with floating interface IP mentioned as in above screenshot. Refer to Default Gateway (IP Routing on Avi SE) for more details.


  • If explicit destination_port or source_portmatch_criteria are not specified by default, then all the ports in the range 1-65535 are allowed.

  • For explicit match-criterion configuration, in the case of both destination_port and source_port match criteria, a maximum of eight port configurations are allowed.

Outbound NAT Use Case

The following are the 3 options of outbound NAT use case:

  • NAT Flows
  • NAT Policy Stats
  • NAT Stat

[admin:localhost.localdomain]: > show serviceengine Active_Standby-se-xyjud nat
nat-flows             Show NAT flow information
natpolicystats        show NAT policy stats
natstat               Show NAT statistics

Note: Starting with Avi Vantage version 18.2.5, the stats are available via CLI.

Match Criteria

The following match criteria options are supported:

  • Match source IP address
  • Match source IP address range
  • Match source IP address group
  • Match source IP prefix
  • Match source port(s). Port range is not supported.
  • Match destination IP address
  • Match destination IP address range
  • Match destination IP address group
  • Match destination IP prefix
  • Match destination port(s)

For every option above, is not option is available. This option can be used to exclude packets having certain parameters from matching the rule.

Match Operations

  1. If two or more of the same parameters are used as match criteria, then OR operation is used for matching.


     source_ip match_criteria is_in
     ranges begin end

    This will match if source IP is or if the source IP falls in the range of -

  2. If two different parameters are used in the match criteria, then AND operation is used for matching.


     source_ip match_criteria is_in
     ranges begin end
     destination_port match_criteria is_in
     ports 80

    This will match if source IP is or if the source IP falls in the range of - and if destination port is 80.

  3. If there are multiple rules configured, the rules are evaluated in the ascending order as indexed. The evaluation stops on first match. No subsequent rules are checked if a packet already matches a rule.

Action Options

  • NAT IP - can be Avi VIP, floating interface IP, IP address in the subnet of SE interface. NAT IP cannot be SE interface IP.
  • NAT IP range.

Document Revision History

Date Change Summary
January 31, 2023 Added 'Configuring NAT Policy using UI' section for 22.1.3 release
February 29, 2024 Added Notes in 'Configuring NAT Policy using CLI' section for 22.1.6 release