A Few Words About Content Caches and Proxies
Content-caching architectures and engines such as in the Cisco product palette deal with the challenge to deliver content reliably, efficiently, and effectively to the network edge and access layer where customers subscribe to certain content. Vice versa, they are necessary to provide sufficiently clustered server farms to feed these requests.
NOTE
Historically, caching was the initial purpose of proxies and proxy chaining. Protection of expensive and rare WAN bandwidth was their prime directive. Today, with cheap bandwidth in abundance, the focus has shifted toward intelligent security, content screening, and load-balancing content and cache-engine architectures. However, these are Layer 4 through 7 issues and not the focus of this chapter. For a background on caching strategies, look at the Internet's most popular open-source proxy, squid, at http://www.squid-cache.org/, and the proxy capabilities of the Apache web server, at http://www.apache.org.
Modern proxies fall in different categories:
- Transparent caching proxies
- Security (intercepting) proxies
- Load-balancing proxies
- Mangling proxies (packet rewrites)
Cisco HA and Load-Balancing Approaches
Cisco offers several architectural approaches to high availability, ranging from lower-layer concepts such as resilient packet ring and Multiprotocol Label Switching (MPLS) node protection up to protocol-intrinsic or application layer approaches.
The lower-layer concepts (Layers 1 through 3) are summarized under the Cisco Global Resilient IP Framework (GRIP). This framework consists of the following building blocks:
- Stateful NAT (SNAT) for translation groups
- IPSec stateful failover (VPN HA in combination with HSRP)
- Multicast subsecond convergence
- GLBP
- Nonstop forwarding with stateful switchover
- MPLS fast reroute
Approaches that are relevant to the transport and application layers are discussed briefly in the following two subsections.
Cisco IOS Server Load Balancing (SLB) Feature
The Cisco IOS SLB feature is available for certain Cisco IOS routers and catalyst switches. It provides two load-balancing algorithms: weighted round-robin and weighted least connections. With SLB enabled, a virtual server (VIP) represents a cluster of real servers. Clients are configured to connect to the IP address of the virtual server (directed or dispatched redirection mode). DNS records usually point to the virtual IP address.
The Cisco IOS SLB intelligence picks a real server to satisfy the requesting client based on one of the load-balancing algorithms mentioned earlier. It can perform NAT, provide added security by hiding real servers, and provide rudimentary DoS protection such as maximum connection limits and SYNGuard (SYN flooding protection).
IOS SLB for Layer 3 switches works with HSRP to prevent single points of failure for virtual IP addresses. In contrast to crude round-robin approaches, the cluster constituents provide input into the IP load-balancing device by means of the Dynamic Feedback Protocol (DFP), indicating the level of CPU utilization, application, and user identity. DFP is implemented with workload agents (Windows, UNIX) that reside on IP server platforms. For further configuration information, consult the Cisco.com document "Configuring Server Load Balancing."
Cisco Content Networking Devices and Software
These devices, software and hardware, operate at Layers 4 through 7 and consist of the following products:
- Content engines
- Content routers (redirect the user to the most suitable site on a network based on a set of metrics such as delay topology, server load, and a set of policies such as location of content)
- Content networking software (carries out the same duty without a dedicated appliance)
The main features of these approaches are caching, intelligent content delivery, traffic distribution, intelligent DNS services, and load balancing.
If You Enjoyed This Post Please Take a Second To Share It.
You Might Also Like
Stay Connected With Free Updates
 |
 |
 |
|
Subscribe via Email
|
