Transparent Web Cache Redirect on the SmartSwitch Router
By Bill Ryan
SmartSwitch Router Product Manager
Introduction
Access to the Internet has gone from a luxury to a necessity in
today's business environment. This has resulted in a tremendous
increase in enterprise and service provider traffic. Quite
often, this is redundant information being transferred. For
example, users may access the same pages over and over. One
costly solution is to just keep adding more bandwidth. However,
WAN access is expensive, whether you're an enterprise owner or a
service provider.
Simply adding bandwidth is just a "band-aid"
solution, and does not address the core problem: the increased
volume of duplicate data. It simply covers up the issue, causing
the same problem to reoccur. Caching web objects preserves
bandwidth by reducing the number of duplicate requests sent out
over WAN links. This paper addresses various caching schemes and
discusses the advantages of the transparent web cache feature of
the SmartSwitch Router 2000, 8000 and 8600.
Quick Overview of Cache Server Types
A Web Cache Server caches HTTP objects. It resides either
directly in the path to the Internet, monitoring all traffic; or
to the side with only HTTP traffic redirected to it (see Figure
1). When the cache server sees the first request for an object,
it sends the request to the intended web site, and caches the
reply in its memory. The next time the Web Cache Server sees a
request for that same object, it traps the request and responds
to the client with the locally stored object, with the
responding packet appearing to have come from the requested
server. Most Web Cache Servers set time limits on how long an
object is stored locally. There are many different Web Cache
Server vendors, and how they maintain their caches is beyond the
scope of this paper. What's important here is how the
SmartSwitch Router enhances a Web Cache Server in the network.
When the Web Cache Server sits in the Internet path, it sees
all the network traffic to the Internet. The benefit to this
solution is that it is transparent to the clients accessing the
network. That is, there is no need to program the clients to
send their traffic to the Web Cache Server. The down side,
however, is that it processes other forms of traffic besides
HTTP, which may cause performance degradation and also
introduces an unnecessary point of failure into the network. For
these reasons, this configuration is not recommended.
The alternative is to have the Web Cache Server positioned
peripheral to the network, with only HTTP traffic directed to
it. This removes the bottleneck caused by other network traffic,
since only HTTP traffic is redirected to the server. Initial
solutions required that all clients on the network be configured
to send their HTTP requests to the Web Cache Server. As a
result, the network administrator needed to configure every
client on the network to send HTTP requests to the Web Cache
Server and all other Internet traffic through normal paths.
Aside from the onerous task of configuring these systems, there
was the added problem that some of these Web Cache Servers could
only support a few thousand connections at a time. Once these
limits were met, new sessions were dropped. Additionally, if the
server went down, HTTP traffic stopped. This obviously has a
negative impact on customers. The solution is transparent web
cache redirection.
Transparent Web Cache Redirect
Transparent web cache redirect on the SmartSwitch Router
addresses these issues. Instead of reconfiguring all of the
clients, the network administrator needs only to configure the
SmartSwitch Router. With a few commands, the administrator can
transparently redirect all HTTP traffic or specific HTTP traffic
to a Web Cache Server. The SmartSwitch Router may be configured
to keep track of the number of current sessions connected to the
Web Cache Server and compare that to a preset maximum number of
connections the server can support. Once the maximum is reached,
new traffic is sent directly to the Internet, bypassing the Web
Cache Server until the number of sessions falls below the
threshold.
Advanced Web Cache Redirect Features
When they receive a request for an object not already in its
memory, some servers make requests to the web site on the
Internet using the Web Cache Server's IP address as the source
address.There are some web sites that use the source IP address
for accounting purposes or for access control. Since some Web
Cache Servers modify the source IP address, the web site may see
this as an invalid address and respond with an error message.
The Web Cache Server would then incorrectly cache the error
message for future requests. The SmartSwitch Router can be
configured so that traffic destined for such sites is sent
directly to the site, not through the Web Cache Server.
There may also be instances when a proxy server is used for
HTTP requests. It may be configured to receive requests with a
port address other than 80 for HTTP traffic, and then its HTTP
requests would be sent to the Internet using port 80. In this
situation, the SmartSwitch Router can be configured to redirect
traffic other than to port 80. The SmartSwitch Router would sit
between the proxy and the clients. As traffic is sent to the
proxy, the SmartSwitch Router would redirect it to the Web Cache
Server based on the different port number. The Web Cache Server,
after being configured to recognize this new port number, would
process the packet in its normal fashion.
Some sites may be concerned that one Web Cache Server is
handling all of the traffic. The SmartSwitch Router solves this
problem. The system administrator can organize a group of Web
Cache Servers into a pool, and the SmartSwitch Router will load
balance the redirection of HTTP traffic over the pool of Web
Cache Servers.
Sample Configurations
The Web Cache Server and the SmartSwitch Router may be located
either at the enterprise or the service provider level. They
could also be placed at both locations, with commonly accessed
pages for a single enterprise kept at the enterprise level, and
commonly requested pages for multiple enterprises kept at the
service provider level. The enterprise manager frees up valuable
bandwidth by cutting down the amount of duplicate web object
traffic. Optimizing the bandwidth on the access lines has the
immediate benefit of delaying the need for adding new access
lines. The service provider frees up valuable bandwidth for
accessing the Internet by reducing the amount of duplicate web
object traffic, and has the benefit of less duplicate traffic
from enterprise customers. In both cases, there is an immediate
improvement in the available bandwidth for WAN traffic.
The best way to illustrate this is through examples. Suppose
that an enterprise manager has purchased a SmartSwitch Router
8600 and a Web Cache Server. The Web Cache Server has an IP
address of 186.89.10.51 and access to the Internet is on
interface ip1 (see figure 2). The selected Web Cache Server
supports 10,000 active connections. There is no HTTP proxy
server and only one Web Cache Server installed. Some of the
users access the web site www.cabletron.com at 188.83.115.10.
The site checks the source address to confirm that the client is
allowed access. While in the configuration mode on the
SmartSwitch Router, the following commands would be entered;
web-cache c1 create server-list s1 list 186.89.10.51
web-cache c1 set-maximum-connection s1 10000
web-cache c1 create bypass-list list 188.83.115.10
web-cache c1 apply interface ip1
These commands create a web cache redirect with the name c1
and a server list associated with it of the name s1. The
server list s1 has only one Web Cache Server entry,
186.89.10.51. The set-maximum-connection command sets the total
number of active connections spread out over the server list s1
(containing only one server) at 10,000. The bypass list allows
traffic destined to address 188.83.115.10 to be sent directly to
the Internet, and not redirected to the Web Cache Server. It is
also possible to apply an ACL profile on the traffic instead of
a specific address (or list or range of addresses). This is
accomplished by replacing 'list 188.83.115.10' with 'profile
p1,' where p1 is the name of the profile to apply.
Web Cache Server load balancing is accomplished by putting a
list of the IP addresses of the Web Cache Servers within
quotation marks. The example below shows how to configure the
SmartSwitch Router if there were two Web Cache Servers in the s1
list, and traffic with port 81 needed redirection as well. The
commands are entered when the SmartSwitch Router is in
configuration mode.
web-cache c1 create server-list s1 list "186.89.10.51
186.89.10.52"
web-cache c1 set-maximum-connection s1 10000
web-cache c1 set http-port 81
web-cache c1 create bypass-list list 188.83.115.10
web-cache c1 apply interface ip1
Conclusion
These simple commands unleash dramatic performance increases on
the network. The SmartSwitch Router harnesses the power of a Web
Cache Server, and makes critical performance-enhancing processes
truly transparent to clients on the network. Using the
transparent redirect feature of the SmartSwitch Router
simplifies the implementation of a Web Cache Server. The
redirection feature alleviates concerns over Web Cache Servers
becoming single points of failure on the network by integrating
redundancy and override features. Additionally, using a Web
Cache Server improves response time by bringing data closer to
clients, and increases available WAN bandwidth by removing
redundant traffic.When this is added to other features found in
the SmartSwitch Router, such as VRRP for redundancy, QoS for
traffic shaping, IP policy routing for security, and traffic
management at wire speed, the administrator sees a tremendous
return on their investment in a SmartSwitch Router 2000, 8000 or
8600 product.
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