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Manual Chapter: Managing the Settings for Subnet Discovery
Manual Chapter
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Overview: Managing advertised routing

An advertised route is a subnet that can be reached through a iSession connection. After the iSession connection is configured between two BIG-IPs, they automatically exchange advertised route specifications between the endpoints. The local endpoint needs to advertise the subnets to which it is connected so that the remote endpoint can determine the destination addresses for which traffic can be optimized. Advertised routes configured on the local endpoint become remote advertised routes on the remote endpoint; that is, the BIG-IP on the other side of the WAN.

When a BIG-IP device is deployed in a large scale network with large number of servers, and many of them belong to different subnets, manually configuring local optimization subnets can be very time consuming. Subnet Discovery is designed to ease such configuration challenges. With local subnet discovery, instead of requiring manual configuration of local subnets for traffic optimization, the BIG-IP system automatically discovers the local optimization subnet when traffic flows from the client side BIG-IP device to a server-side BIG-IP device.

Task Summary

Perform these tasks to manage advertised routing

Task list

Adding a virtual server to advertised routes

You can add the IP address of a virtual server you created to intercept application traffic to the list of advertised iSession routes on the central BIG-IP system. This configuration tells the BIG-IP system in the remote location that the iSession-terminating endpoint on the central BIG-IP system can route traffic to the application server.
  1. On the Main tab, click Acceleration > Symmetric Optimization > Advertised Routes.
  2. Click Create. The New Advertised Routes screen opens.
  3. In the Name field, type a name for a the advertised route (subnet).
  4. In the Address field, type the IP address of the virtual server you created for accelerating application traffic.
  5. In the Netmask field, type 255.255.255.255.
  6. Click Finished.
The remote BIG-IP system now knows that the iSession-terminating endpoint on the central BIG-IP system can route traffic to the application server.
Verify that the iSession profile on the iSession-terminating (endpoint) virtual server is configured to target this virtual server. The default profile isession, for which the default Target Virtual setting is match all is appropriate, as long as the Address setting for this virtual server is not a wildcard (0.0.0.0).

Adding advertised routes manually

An advertised route is a subnet that can be reached through the local endpoint. You can add advertised routes manually, for example, if you disabled the Discovery setting on the Quick Start screen.
  1. On the Main tab, expand WAN Optimization and click Advertised Routes.
  2. Click Create. The New Advertised Routes screen opens.
  3. In the Name field, type a name for the subnet.
  4. In the Address field, type the IP address of the subnet.
  5. In the Netmask field, type the subnet mask.
  6. In the Label field, type a descriptive label to identify the subnet.
  7. For the Mode setting, specify whether traffic on the subnet is included in optimization. If you select Excluded, the local and remote endpoints exchange subnet configuration information, but traffic on this subnet is excluded from optimization.
    Note: You can define a subset of IP addresses to exclude from optimization within a larger included subnet. An excluded endpoint advertised route must be a valid address range subset of an included endpoint advertised route.
  8. Depending on how many advertised routes you want to add, click the appropriate button.
    Option Description
    Repeat Save this route and add more advertised routes.
    Finished You have finished adding advertised routes.

Modifying automatic discovery of advertised routes

You can modify the settings that pertain to the discovery of subnets that can be reached through the local endpoint. These settings determine how BIG-IP learns about discovered subnets, and when to display the subnets. Using these settings, you can control the number and reach of the discovered subnets that are included.
  1. On the Main tab, click WAN Optimization > Advertised Routes > Discovery.
  2. From the Configuration list, select Advanced to view all the settings.
  3. Ensure that the Discover Routes check box is selected.
    Note: For server discovery to take place, the setting Discover Other Endpoints on the Remote Endpoints Dynamic Discovery screen, at the other end of the connection, must not be set to Disabled.
  4. In the Stop discovery after field, type the maximum number of servers or subnets (advertised routes) you want the system to discover before it stops looking.
  5. In the Do not add servers with RTT greater than field, type the maximum round-trip time in milliseconds. The system does not add discovered servers that have an RTT over this value.
  6. In the Minimum prefix length for IPv4 address field, type the minimum prefix length for route aggregation in IPv4 networks. If you use the default value of 32/128, the BIG-IP adds the host address as the advertised route. If you change this value to 24, the system adds the /24 network in which the server resides as the advertised route.
  7. In the Minimum prefix length for IPv6 address field, type the minimum prefix length for route aggregation in IPv6 networks.
  8. In the Allow idle time for routes field, specify the minimum and maximum lengths of time a discovered route can be idle (no optimized traffic coming through) without being removed. You can specify these limits in days, hours, or minutes, and the unit of measure must be the same for both limits. This setting does not affect manually configured routes.
  9. In the Do not add routes with ip ttl less than field, leave the default value of 5, or type a number between 0 and 255. The BIG-IP system matches the value you set with the IP TTL value of the discovery packets from the server. If the packet has an IP TTL value less than the configured value, it means the server is farther away than you want, so the system does not add the advertised route (server).
  10. To save the discovered subnets in the configuration, ensure that the Automatically save discovered routes check box is selected.
  11. In the Filter Mode field, you can exclude from discovery a subset you specify in the Subnet Filter field. You can also narrow the scope of the subnet discovery by selecting Include and specifying only the subnets to include in discovery.
    Important: If you select Include without entering an IP address in the Subnet Filter field, the system does not discover any subnets.
  12. Click Update to save changes.
After the BIG-IP system discovers a subnet and adds the route to the list, the system automatically optimizes traffic to any hosts in that subnet without rediscovery.

Verifying subnet discovery

After sending a client request from the local BIG-IP to a server behind a remote BIG-IP device, you can perform this procedure to verify that the destination subnet is discovered.
  1. Using the browser interface on the client-side BIG-IP system, on the Main tab, click WAN Optimization > Remote Endpoints. The Remote Endpoints List screen opens.
  2. Verify that the status indicator is green, and the IP address is correct for the remote endpoint you are checking.
  3. On the menu bar, click Routes, and verify that the list includes the IP address of the destination subnet. This subnet is also displayed on the Advertised Routes List screen of the browser interface on the server-side BIG-IP system.
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