Oklahoma Disaster Relief
VoyForums Notice -- Quick Contributions:|
Donate $10 to the Red Cross: Text the word REDCROSS to 90999
Donate $10 to the Salvation Army: Text the word STORM to 80888
* The charge will appear on your cellphone bill.
|Problems with Caching Proxy Servers (pronounced "cashing proxee servers")|
- The Symptoms
- What's Wrong?
- How can the problem be remedied?
- Information you should know -- The Basics...
- Caching Proxy Servers are not the Web-Browser
- Last-Modified & Expiration Information
- Dynamic Pages
- The Problem
- What can you do about it?
Missing form variables when posting: This seems to be specifically
related to faulty caching proxy servers not transmitting the user's
post information to VoyForums.
Seeing old pages: Many people have reported that new messages are
not being posted -- this is over 95% of the time not the case,
but is the result of seeing an old version of a message
index among other complications with some servers on Internet failing to
comply with standards. It must be mentioned that VoyForums doesn't have any
way of sending you an "old" forum index, and this paper explains that the
actual location of this problem is usually with your Internet Provider and
their "Caching Proxy Server(s)". Please read-on to learn about the problem
before you contact your ISP.
New messages not posting: As
mentioned above, this is not the actual case, but is just a side-effect of
old pages being seen, or VoyForums not receiving page-requests. Read on to
Many Internet Service Providers (ISPs) use software on their machines to
reduce on network traffic -- they do this by keeping a copy of the webpages
transferred by their users. Known as caching, the technique can be
beneficial to reduce on network load. However, many ISPs use outdated or
flawed caching software (called proxy cache software) which does not
abide by HTTP 1.1 standards. The two main problems are:
- Ignoring when a page's size changes:
Many flawed proxy servers improperly ignore if a webpage changes size.
If a document's size changes, the page should be considered un-fresh,
and updated in the cache.
- Not recognizing dynamic content:
Webpages often include a Last-modified time. Many program-generated
pages include an option specifying to not cache the pages (called
Pages which include no caching information or modification times
should be considered "dynamic" content pages, and proxy servers should
not cache these pages. Why not include the "no-cache" with these pages?
The reason is because this option is used by your web-browser as well,
and using it in a page means the web-browser will reload the page over
the network even if moving backwards and forwards. Using it would
actually consume more bandwidth than if the proxy servers were fixed.
How can the problem be remedied?
The Proxy-Cache software must be fixed/updated by the ISP to comply with
HTTP/1.1 standards. Free software like "Squid" is very-well behaved and
available for use by anyone. In addition, we're told that "ProxyPlus" for
Windows is also just about as good (thanks to Kevin from Remote
Communications for his helpful information). Other software must be
updated so it is compliant with the latest standards.
There is nothing that can be done from a website -- the change must be
made at the ISP. This is because any changes on a website serving dynamic
data either means the data will not be considered dynamic at all (and users
won't see new pages), or will increase on network traffic --
defeating the purpose of the proxy cache servers.
Many ISPs have already updated their software after users reported the
problem, but there are still some that refuse to take action.
Information you should know -- The Basics...
When you view a webpage over Internet, the page is sent through many
devices before it reaches you. Most of these devices do nothing more
than send the information the proper direction (routers, switches,
hubs, etc.) However many Internet Service Providers (ISPs) have
special computers set up which store copies of user-requested
webpages. These computers are known as "caching proxy servers",
"caching proxies," or "caching servers", and they are primarily
used to reduce network traffic by serving pages to users from
a local storage instead of it being transmitted the full distance
How does it reduce network traffic? The idea is simple: Any user(s)
wanting to view a webpage send out their request, but since
the Caching Proxy "sees" this request first, it can check if it
already has that page stored -- if it has that page stored in its
cache, it returns the stored page to the user. This means
the page doesn't have to be transferred from the original source again.
This also means the page may be a bit old.
This usually works fine, and is a marvellous way to reduce network
load on Internet. Unfortunately, some proxies are faulty and do not
follow the standards...
Caching Proxy Servers are not the Web-Browser Cache:
Before we go on, it is important to mention that we have been
discussing machines outside of a user's machine. The most
common "cache" a user hears of is the one his/her browser keeps
on their own machine. This cache stores the pages a user retrieves
and keeps them on their own hard drive and in memory. The problems
we are discussing are predominantly not under the control
of the end-user, and reside outside on Internet. We we will tell you
what you can do about it
at the end of this document.
Last-Modified & Expiration Information:
It is standard practice for web-pages to be transmitted along with
the time the file was last modified. This information is sent by
the site serving the webpage. This merely tells your web-browser or
the proxy server when it is thought the document was last changed,
but doesn't say much about when it will change next.
Additionally, there is another bit of information that can be sent
to tell a cache not to cache. This is an Expires time,
and is used to force a cache to clear this document from its storage
at the specified time.
Web-pages which are created by a program and contain content that
changes often are referred to as "dynamic-content" pages. They often
change the data every time they are loaded. It is standard for such
pages to be transmitted with no last-modified time nor expires
time. Proxy Cache servers are not "supposed" to store these pages.
Proxy Cache servers should also check to see if a page's content-length has
changed -- if it has, they should consider it not-fresh and update their
Although caching servers aren't supposed to cache these pages, they don't
all follow the standards. In particular, older versions of proxy software
tend to be more faulty than newer ones -- they keep the pages stored
even when they shouldn't. The result is that even clicking reload will
load the old stored page from the caching proxy, and the source-site
never receives the request. This means that VoyForums servers never
even receive your request to load the page again -- you're seeing an
old page stored by your ISP.
What can you do about it?
If you suspect you are seeing old pages, it is not VoyForums doing it
but, most likely, you are seeing the stored page from a caching proxy
server. This server probably belongs to your ISP, and is more-than-likely
a server not following the standards.
We have now received word from some of our forum owners that their users
have had this problem fixed after reporting it to their ISP. It is highly
possible that this problem occurs because an ISP is using outdated or
faulty proxy software.
There is nothing we can do about this from our end, although we have
tried. Each method of trying to deal with these non-standard-compliant
proxy-servers has its own complications. After trying numerous work-arounds,
we found it best to leave our site handle things the way it should, and
hope ISPs fix their cache proxies.
[ Back to Help Desk ]
VoyForums(tm) is a Free Service from Voyager Info-Systems.
Copyright © 1998-2012 Voyager Info-Systems. All Rights Reserved.