NETWORK MANAGEMENT
Seeing through transparency claims
Dr. David Hughes
01.03.2007
Rating: -3.50- (out of 5)
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Many Wide Area Network (WAN) acceleration solutions are "symmetric" in nature, requiring communication between devices on each end of a WAN link. In order for these solutions to work, there must be a reliable way for traffic to be encoded/compressed on one end of the WAN link and successfully directed to a device on the other end of the link, where the traffic can be decoded/decompressed before final delivery.
There are two primary ways in which symmetric acceleration devices communicate across a WAN. These are:
Technology comparison
There are advantages and disadvantages to the different methods of communication across a WAN. Header transparency improves visibility into the header, which can be used to enforce downstream ACLs and QoS policies on simple protocols, such as CIFS. It does not provide visibility into the payload, however, and this limits its value when applications use ephemeral ports (e.g., VoIP, FTP and MAPI). In addition, this method can actually be problematic when downstream devices are using deep-packet inspection to compare header information with payload information, and can be costly to deploy and complicated to manage in networks with multiple WAN paths.
With peering, on the other hand, optimized traffic can be distinguished from non-optimized traffic across the WAN. Peering is also less disr
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uptive to IDS/IPS, firewalls and other downstream devices that map headers to payload information. Peering is more robust and reliable because optimized traffic is explicitly directed to the peer, where it is converted back into normal traffic before being forwarded to the end user. However, it does not natively provide visibility into the header, which can sometimes be used to preserve existing policies (i.e., when applications use static ports). This visibility must be provided using additional techniques.
A clear vision for transparency
Both methods described above are effective ways of communicating across a WAN, but neither method -- by itself -- delivers the level of transparency required to preserve all existing policies across a WAN. Any claims to the contrary are deliberately misleading. For a WAN acceleration solution to be truly transparent it must:
To achieve end-to-end transparency, vendors have to augment one of the above communication methods with other techniques. For example, the following can be used in conjunction with peering to provide end-to-end visibility across the WAN:
About the author:
Dr. David Hughes founded Silver Peak Systems in 2004 and previously held senior architect positions with Cisco Systems, Stratacom, Blueleaf and Nortel. He has a PhD in packet network optimization.
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