It is arguably the most important function of a web proxy at least as far as performance is concerned and that’s on-demand caching. That is documents or web pages which are cached upon request by a client or application. It’s important to remember that a document can only be cached if it has actually been requested by a user. Without a request, it will not be cached and indeed the proxy server will not even be aware of it’s existence.
This is a different method than using a replication model which is typically used to distribute data and updates. This is more often used on larger, busier networks where data can be replicated onto specific servers, this method is also known as mirroring and also useful for sharing over the internet. One of the most common examples for mirroring is when a large software package is being distributed instead of a single server being responsible, multiple duplicates are replicated onto different servers.
One of the best ways to facilitate performance increases is to use a method called round-robin DNS. This involves mapping a single host name to multiple physical servers. These servers must be assigned separate IP and physical addresses and their addresses distributed evenly among the clients requesting the software. When using the DNs method, the clients will be unaware of the existence of multiple servers because they will appear as a single logical server.
Most of the caching solutions used by proxies are centred around removing the load on a specific server. However when a proxy caches resources locally without mirroring or replication then it’s still the single server which is responsible. The physical loads doesn’t decrease however it does reduce the number of network requests that the server has to implement. This also reduces the number of name requests that the server makes which can also introduce some levels of latency.
Having caching enabled can reduce the speed of the server responses significantly. However this does depend largely on the sort of requests that are made, imagine a proxy used specifically to obtain a Czech IP Address and directly download a specific resource. Caching that resource locally would improve the speed significantly as long as the content didn’t change much, however this would be different for sites which stream audio or video and contained large amounts of multimedia content.
The SSL Tunneling Protocol allows any proxy server which supports it the ability to act as a tunnel for SSL enhanced protocols. This feature is essential to support normal web traffic and increasingly SSL is being used to secure normal web requests which would previously have been sent in clear text. The client makes the initial HTTP request to the proxy and asks for an SSL tunnel. If we look at the protocol level the actual handshake to establish the SSL tunneling connection is fairly straight-forward.
The connection is simple and in fact looks like virtually any other HTTP request, the only difference is that we use a new ‘Connect’ method. The format is also slightly different as the parameter is not a full url but rather the destination host address and the post number in the format 192.168.1.1:8080. The port number is always required with these connection requests, as the default number is generic and not always correct.
When the client has received a successful response then the connection will pass all data in both directions to the destination server. For the proxy server much of it’s role in authentication and establishing the connection is over, and it’s role is then limited to simply forwarding data for the connection. The final significant role for the proxy server is to close the connection which it will do when it receives a close request from either the client or the server.
Other situations where the connection will be closed mainly refer to error status codes. For example an error generated in response to authentication would be a typical situation where authentication has failed. Most proxies will require some sort of authentication especially the high quality US proxies such as this. The methods might change however from a simple username password supplied via a challenge and response to pass through authentication from a system like the Active Directory or LDAP.
It’s interesting to note that the mechanism used to handle SSL tunnelling is not actually specific to this protocol. It is in fact a generic technique which can be used to tunnel any protocol including SSL. There is no actual reliance on any SSL support from the proxy, which can be confusing when you see people look for SSL enabled proxies online. It is not required on a properly configured proxy server as the data is simply transported there is no need for the actual protocol to be understood after the initial connection request.
There are issues with some protocols transferring through proxies, certain specialised protocols need more support than is offered with the standard tunneling mechanism. For example for many years LDAP (Lightweight Directory Access Protocol) was not able to work across most common proxies. Some implementations support LDAP by using SOCKS while there is some difficulty with LDAP queries being cached and subsequently causing performance issues. Most protocols however work perfectly with this ‘hands off’ tunneling mechanism which you can see perfectly illustrated if you try and stream video through proxies like this which used to circumvent BBC iPlayer blocked abroad.
There is little excuse for not installing an IDS (Intrusion Detection System) on your Network, even the usual culprit of budget doesn’t apply. In fact one of the leading IDS systems called Snort is actually available completely free of charge and is sufficient for all but the most very complex network infrastructures. It is virtually impossible to effectively monitor and control your network, particularly if it’s connected to the internet, without some sort of IDS in place.
There are certain questions about the day to day operation of your network that you should be able to answer. Questions like the following will help you determine if you really have control over your network and it’s hardware =
- Can you tag and determine how much traffic on your network is associated with malware or unauthorised software.
- Are you able to determine which of your clients do not have the latest client build?
- Can you determine which websites are most popularly requested. Are these requests from legitimate users or as a result of malware activity.
- Can you determine which users are the top web surfers (and is it justified).
- How much mail are your SMTP server’s processing?
It is surprising how many network professionals simply wouldn’t have a clue about obtaining this information from their network however, it’s impossible to ensure that the network is efficient without it. For example a few high intensive web users can create much more traffic than the majority of ordinary business users. Imagine two or three users in a small department who used a working BBC VPN to stream TV to their computer 8 hours a day. The traffic that would generate would be huge and could easily swamp an important network segment.
All security professionals should ensure that they have the tools and reporting capacity to answer simple questions like this about network usage. Knowing the answers to these questions, will help control and adapt your network to meet it’s users needs. Of course a simple IDS won’t provide the complete solution but it will help keep control in your network. Malware can sit and operate for many weeks in a network which is not monitored properly. This will heavily impact performance and can enable it to spread to other devices and eventually other networks. In network environments where performance is important, then being aware of the sorts of situations can make a huge difference.
Network Professional and Broadcaster on author of BBC News Streaming.
In these times when security is becoming ever more important the SSL Tunneling Protocol is extremely important, it allows a web proxy server to act as a tunnel for SSL enhanced protocols. The protocol is used when any connected client makes a HTTP request to the proxy server and asks for a SSL tunnel to be initiated. On the HTTP protocol level, the handshake required to initiate the SSL tunneling connection is simple. There is little difference to an ordinary HTTP request except that a new ‘Connect’ method is used and the parameter passed is not a full URL but instead a destination port number and hostname separated by a colon.
The port number is always required with ‘CONNECT’ requests because the tunneling method is generic and there is no protocol specified, hence default port numbers cannot be used reliably. The general syntax for the request is as below ;
CONNECT <host>:<port> HTTP/1.0
HTTP Request Headers
The successful response would be a connection established message, followed by another empty line. After the successful response the connection will then pass all the data transparently to the destination server and pass through any replies from the server. In practice what is happening is the proxy is validating the initial request, establishes the connection and then takes a step back. After this initial stage the proxy merely forwards data back and forth between the client and the server. If either side closes the connection then the proxy will cause both connections to be closed and no mor tunneling will take place until a new connection is established between the server and client.
The proxy does have the ability to respond to error messages within the SSL tunnel. If this error is generated in the initial stages then the connection will not be established, if it is already connected then the proxy will close the connection after the error response has been sent. However it is important to remember especially where security is important that this SSL tunneling protocol is not specific to SSL and therefore has no in depth security. The tunnelling mechanism used in this instance is a generic one and can in fact be used for any protocol. This means that there is no requirement either for the proxy to support SSL either as the server is merely establishing a connection and then forwarding data without any processing.
BBC Iplayer Ireland – Here’s How you Can Watch
The network layer of the OS Protocol stack is often simply known as Layer 3. It is important for network troubleshooting as it is where routing takes place one level above the data link layer (Layer 2) which is where switching and bridging happens. A VLAN (virtual LAN) is a subnetwork of an internetwork however it is normally defined using a switched network topology.
So what do we mean by a switched network? Well simply put it is a series of devices such as computers attached directly to some sort of multiport switching device. A network switch acts like a connecting medium between the ports which computers are connected to. In the perfect switching environment each port has only one device connected to it, however in reality it’s likely to be another network device like a bridge or hub which has many more clients indirectly connected to the switch. The perfect scenario has no conflict between different devices trying to use the same network cable, performance is maximized here because there is no waiting or latency while information is transmitted such as you would get on Ethernet. Just like the simple VPNs we use across the internet to watch BBC USA whilst hiding your IP address they VLANs segment and protect traffic.
An important reason for segmenting networks initially then connecting them together again using routers is that it minimizes the size of broadcast domains with fewer devices competing for access. Switched topologies also reduce the level of contention and many networks have to evolve into large flat switched networks. If you remove routers though there is a price to pay both in ease of administration and being able to securely manage specific segments or devices. If you need to retain some sort of topological layout in this scenario, VLANs are probably the only feasible option.
A VLAN restores the advantages of a segmented network to a flat switched network. Network administrators can use VLANs to create pseudo segments in a open network across the switches. This is important for creating security segments and managing large networks as the computers which are joined to the VLAN can exists anywhere on the network. So for example you can create a high security VLAN to connect secured servers together where they can be managed and secured as a group. These servers can exist on different switches, different ports and across buildings and departments.
The next stage is to take these individual VLANs which connect many groups of computers and extend the model. Indeed a device can be a member of multiple VLANs and messages can be broadcast to specific devices by sending them to specific VLANs only. The issue with this setup is that routers still need to transmit packets across these different VLANs, there is still a requirement for data to be transported which can cause contention and performance issues.
Here we see the techniques of Layer 3 switching being useful where a routing algorithm is used to discover the fastest path through the switched network. Once a destination is actually located, a shorter layer 2 switched path can be used. This procedure is possible because the VLANS will actually overlay the physical switching fabric of the network. Obviously there is more to these techniques and indeed the design and construction of efficient switched networks is a large and interesting field.
John Simmons, american version of Netflix? Galsworthy Publications, 2013
The technology sector is at the moment somewhat confused about what a VPN actually is. However the confusion is understandable as the VPN has continually evolved over the last few years into a somewhat different networking technology. In the passed, the VPN could be described as a private network which is able to carry voice and data usually built into existing carrier services.
This is not how a VPN is defined commonly today, it’s probably best to split into the following different definitions.
- Voice VPN – a single carrier which handle all the voice call switching. The ‘virtual’ in VPN here implies that a virtual voice switching network has been created within the switching equipment. This is probably the most dated definition under the concept of traditional carrier based voice vpns.
- Carrier Based Data VPN – Traditional packet, cell switching and frame networks normally carry data in discrete bundles which are then routed through a complex mesh of networks and switches to their destination. These networks would be shared between many owners and users. A VPN would be a web of individual virtual circuits which form a virtual private network over another carriers packet-switched network.
- Internet VPN – this is probably the definition which is most relevant today, similar to the previous carrier based data network. Here an IP network is the underlying transport and the common medium the shared hardware of the internet.
The internet VPN like this is the most common today probably because it is by far the easiest and cheapest one to set up. There might not be the same bandwidth and data quality guarantees than a traditional virtual circuit, however the popularity of simple VPN client and server accessible from anywhere in the world is a powerful tool for many reasons.
What’s more the internet VPN can be created and used by almost anyone without exception. Companies for instance will often install generic VPN client software on their laptops so any employee can dial in to the corporate servers using any internet connection safely and securely. This means that employees can work remotely from almost any location all they need is a simple internet connection and an account on the VPN server.
A decade ago these were used over simple dial up modems but now most countries have a fairly large internet access infrastructure allowing high speed access from most public places and from home internet connection. The other advantage is that an internet VPN requires no real investment in hardware apart from the central server. Users can leverage the internet connection of their ISP or even a hotel wifi access point, a fairly insecure setup but if you connect through a virtual private network then all your data is securely encrypted and protected from prying eyes.