Category Archives: FortiOS

WAN optimization, web caching and memory usage

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WAN optimization, web caching and memory usage

To accelerate and optimize disk access and to provide better throughput and less latency FortiOS WAN optimization uses provisioned memory to reduce disk I/O and increase disk I/O efficiency. In addition, WAN optimization requires a small amount of additional memory per session for comprehensive flow control logic and efficient traffic forwarding.

When WAN optimization is enabled you will see a reduction in available memory. The reduction increases when more WAN optimization sessions are being processed. If you are thinking of enabling WAN optimization on an operating FortiGate unit, make sure its memory usage is not maxed out during high traffic periods.

In addition to using the system dashboard to see the current memory usage you can use the get test wad 2 command to see how much memory is currently being used by WAN optimization. See “get test {wad | wccpd} <test_level>” for more information.

WAN optimization and HA

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WAN optimization and HA

You can configure WAN optimization on a FortiGate HA cluster. The recommended best practice HA configuration for WAN optimization is active-passive mode. When the cluster is operating, all WAN optimization sessions are processed by the primary unit only. Even if the cluster is operating in active-active mode, HA does not load-balance WAN optimization sessions.

You can also form a WAN optimization tunnel between a cluster and a standalone FortiGate unit or between two clusters.

In a cluster, only the primary unit stores the byte cache database. This database is not synchronized to the subordinate units. So, after a failover, the new primary unit must rebuild its byte cache. Rebuilding the byte cache can happen relatively quickly because the new primary unit gets byte cache data from the other FortiGate unit that it is participating with in WAN optimization tunnels.

WAN optimization and user and device identity policies, load balancing and traffic shaping

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WAN optimization and user and device identity policies, load balancing and traffic shaping

Please note the following about WAN optimization and firewall policies:

  • WAN optimization is not compatible with firewall load balancing.
  • WAN optimization is compatible with source and destination NAT options in firewall policies (including firewall virtual IPs). If a virtual IP is added to a policy the traffic that exits the WAN optimization tunnel has its destination address changed to the virtual IPs mapped to IP address and port.
  • WAN optimization is compatible with user identity-based and device identity security policies. If a session is allowed after authentication or device identification the session can be optimized.

 

Traffic shaping

Traffic shaping works for WAN optimization traffic that is not in a WAN optimization tunnel. So traffic accepted by a WAN optimization security policy on a client-side FortiGate unit can be shaped on ingress. However, when the traffic enters the WAN optimization tunnel, traffic shaping is not applied.

 

In manual mode:

  • Traffic shaping works as expected on the client-side FortiGate unit.
  • Traffic shaping cannot be applied to traffic on the server-side FortiGate unit. In active-passive mode:
  • Traffic shaping works as expected on the client-side FortiGate unit.
  • If transparent mode is enabled in the WAN optimization profile, traffic shaping also works as expected on the server-side FortiGate unit.
  • If transparent mode is not enabled, traffic shaping works partially on the server-side FortiGate unit.

WAN optimization tunnels

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WAN optimization tunnels

All optimized traffic passes between the FortiGate units or between a FortiClient peer and a FortiGate unit over a WAN optimization tunnel. Traffic in the tunnel can be sent in plain text or encrypted using AES-128bit-CBC SSL.

 

WAN optimization tunnels

Both plain text and the encrypted tunnels use TCP destination port 7810.

Before a tunnel can be started, the peers must be configured to authenticate with each other. Then, the client- side peer attempts to start a WAN optimization tunnel with the server-side peer. Once the peers authenticate with each other, they bring up the tunnel and WAN optimization communication over the tunnel starts. After a tunnel has been established, multiple WAN optimization sessions can start and stop between peers without restarting the tunnel.

 

Tunnel sharing

You can use the tunnel-sharing WAN optimization profile CLI keyword to configure tunnel sharing for WAN optimization rules. Tunnel sharing means multiple WAN optimization sessions share the same tunnel. Tunnel sharing can improve performance by reducing the number of WAN optimization tunnels between FortiGate units.

Having fewer tunnels means less data to manage. Also, tunnel setup requires more than one exchange of information between the ends of the tunnel. Once the tunnel is set up, each new session that shares the tunnel avoids tunnel setup delays.

Tunnel sharing also uses bandwidth more efficiently by reducing the chances that small packets will be sent down the tunnel. Processing small packets reduces network throughput, so reducing the number of small packets improves performance. A shared tunnel can combine all the data from the sessions being processed by the tunnel and send the data together. For example, suppose a FortiGate unit is processing five WAN optimization sessions and each session has 100 bytes to send. If these sessions use a shared tunnel, WAN optimization combines the packets from all five sessions into one 500-byte packet. If each session uses its own private tunnel, five 100-byte packets will be sent instead. Each packet also requires a TCP ACK reply. The combined packet in the shared tunnel requires one TCP ACK packet. The separate packets in the private tunnels require five.

Use the following command to configure tunnel sharing for HTTP traffic in a WAN optimization profile.

config wanopt profile edit default

config http

set tunnel-sharing {express-shared | private | shared}

end

 

Tunnel sharing is not always recommended and may not always be the best practice. Aggressive and non- aggressive protocols should not share the same tunnel. An aggressive protocol can be defined as a protocol that is able to get more bandwidth than a non-aggressive protocol. (The aggressive protocols can “starve” the non- aggressive protocols.) HTTP and FTP are considered aggressive protocols. If aggressive and non-aggressive protocols share the same tunnel, the aggressive protocols may take all of the available bandwidth. As a result, the performance of less aggressive protocols could be reduced. To avoid this problem, rules for HTTP and FTP traffic should have their own tunnel. To do this, set tunnel-sharing to private for WAN optimization rules that accept HTTP or FTP traffic.

It is also useful to set tunnel-sharing to express-shared for applications, such as Telnet, that are very interactive but not aggressive. Express sharing optimizes tunnel sharing for Telnet and other interactive applications where latency or delays would seriously affect the user’s experience with the protocol.

Set tunnel-sharing to shared for applications that are not aggressive and are not sensitive to latency or delays. WAN optimization rules set to sharing and express-shared can share the same tunnel.

Operating modes and VDOMs

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Operating modes and VDOMs

To use WAN optimization, the FortiGate units can operate in either NAT/Route or Transparent mode. The client- side and server-side FortiGate units do not have to be operating in the same mode.

As well, the FortiGate units can be configured for multiple virtual domain (VDOM) operation. You configure WAN optimization for each VDOM and configure one or both of the units to operate with multiple VDOMs enabled.

If a FortiGate unit or VDOM is operating in Transparent mode with WAN optimization enabled, WAN optimization uses the management IP address as the peer IP address of the FortiGate unit instead of the address of an interface.

FortiClient WAN optimization

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FortiClient WAN optimization

PCs running the FortiClient application are client-side peers that initiate WAN optimization tunnels with server- side peer FortiGate units. However, you can have an ever-changing number of FortiClient peers with IP addresses that also change regularly. To avoid maintaining a list of such peers, you can instead configure WAN optimization to accept any peer and use authentication to identify FortiClient peers.

Together, the WAN optimization peers apply the WAN optimization features to optimize the traffic flow over the WAN between the clients and servers. WAN optimization reduces bandwidth requirements, increases throughput, reduces latency, offloads SSL encryption/decryption and improves privacy for traffic on the WAN.

For more details, see FortiClient WAN optimization on page 2904.

WAN optimization transparent mode

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WAN optimization transparent mode

WAN optimization is transparent to users. This means that with WAN optimization in place, clients connect to servers in the same way as they would without WAN optimization. However, servers receiving packets after WAN optimization “see” different source addresses depending on whether or not transparent mode is selected for WAN optimization. If transparent mode is selected, WAN optimization keeps the original source address of the packets, so servers appear to receive traffic directly from clients. Routing on the server network should be configured to route traffic with client source IP addresses from the server-side FortiGate unit to the server and back to the server-side FortiGate unit.

Some protocols, for example CIFS, may not function as expected if transparent mode is not selected. In most cases, for CIFS WAN optimization you should select trans- parent mode and make sure the server network can route traffic as described to sup- port transparent mode.

If transparent mode is not selected, the source address of the packets received by servers is changed to the address of the server-side FortiGate unit interface that sends the packets to the servers. So servers appear to receive packets from the server-side FortiGate unit. Routing on the server network is simpler in this case because client addresses are not involved. All traffic appears to come from the server-side FortiGate unit and not from individual clients.

Do not confuse WAN optimization transparent mode with FortiGate transparent mode. WAN optimization transparent mode is similar to source NAT. FortiGate Transparent mode is a system setting that controls how the FortiGate unit (or a VDOM) processes traffic.

 

Configuring Transparent mode

You can configure transparent mode by selecting Transparent in a WAN Optimization profile. The profile is added to an active WAN Optimization policy.

When you configure a passive WAN Optmization policy you can accept the active policy transparent setting or you can override the active policy transparent setting. From the GUI you can do this by setting the Passive Option as follows:

  • default use the transparent setting in the WAN Optimization profile added to the active policy (client-side configuration).
  • transparent impose transparent mode (override the active policy transparent mode setting). Packets exiting the FortiGate keep their original source addresses.
  • non–transparent impose non-transparent mode (override the active policy transparent mode setting). Packets exiting the FortiGate have their source address changed to the address of the server-side FortiGate unit interface that sends the packets to the servers.

 

From the CLI you can use the following command:

config firewall policy

set wanopt-passive-opt {default | transparent | non-transparent}

end

Byte caching

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Byte caching

Byte caching breaks large units of application data (for example, a file being downloaded from a web page) into small chunks of data, labelling each chunk of data with a hash of the chunk and storing those chunks and their hashes in a database. The database is stored on a WAN optimization storage device. Then, instead of sending the actual data over the WAN tunnel, the FortiGate unit sends the hashes. The FortiGate unit at the other end of the tunnel receives the hashes and compares them with the hashes in its local byte caching database. If any hashes match, that data does not have to be transmitted over the WAN optimization tunnel. The data for any hashes that does not match is transferred over the tunnel and added to that byte caching database. Then the unit of application data (the file being downloaded) is reassembled and sent to its destination.

The stored byte caches are not application specific. Byte caches from a file in an email can be used to optimize downloading that same file or a similar file from a web page.

The result is less data transmitted over the WAN. Initially, byte caching may reduce performance until a large enough byte caching database is built up.

To enable byte caching, you select Byte Caching in a WAN optimization profile.

Byte caching cannot determine whether or not a file is compressed (for example a zip file), and caches compressed and non-compressed versions of the same file separately.

 

Dynamic data chunking for byte caching

Dynamic data chunking can improve byte caching by improving detection of data chunks that are already cached in changed files or in data embedded in traffic using an unknown protocol. Dynamic data chunking is available for HTTP, CIFS and FTP.

Use the following command to enable dynamic data chunking for HTTP in the default WAN optimization profile.

 

config wanopt profile edit default

config http

set prefer-chunking dynamic

end

 

By default dynamic data chunking is disabled and prefer-chunking is set to fix.