Protocol optimization
Protocol optimization techniques optimize bandwidth use across the WAN. These techniques can improve the efficiency of communication across the WAN optimization tunnel by reducing the amount of traffic required by communication protocols. You can apply protocol optimization to CIFS, FTP, HTTP, MAPI, and general TCP sessions. You can apply general TCP optimization to MAPI sessions.
For example, CIFS provides file access, record locking, read/write privileges, change notification, server name resolution, request batching, and server authentication. CIFS requires many background transactions to successfully transfer a single file. This is usually not a problem across a LAN. However, across a WAN, latency and bandwidth reduction can slow down CIFS performance.
When you select the CIFS protocol in a WAN optimization profile, the FortiGate units at both ends of the WAN optimization tunnel use a number of techniques to reduce the number of background transactions that occur over the WAN for CIFS traffic.
If a policy accepts a range of different types of traffic, you can set Protocol to TCP to apply general optimization techniques to TCP traffic. However, applying this TCP optimization is not as effective as applying more protocol-specific optimization to specific types of traffic. TCP protocol optimization uses techniques such as TCP SACK support, TCP window scaling and window size adjustment, and TCP connection pooling to remove TCP bottlenecks.
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, labeling 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, 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 can only be enabled from the CLI and is available for HTTP, CIFS and FTP.
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Dynamic data chunking is disabled by default and |
To enable dynamic data chunking for HTTP in the default WAN optimization profile:
config wanopt profile
edit default
config http
set prefer-chunking dynamic
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