Knowledge Base

Proactive customer success initiatives

Spitfire is committed to providing the best possible support and guidance to our customers, drawing from years of experience to share network security concerns, industry insights, best practices and White Papers.  We also provide a comprehensive resource of FAQs, installation instructions, product manuals and user guides.

If you can’t find what you’re looking for, please don’t hesitate to contact us.


Problems with VPN/ transferring data over VPN

The MAX product provides download data rates of up to 8Mb/s with Maximum upload data rates from 256 kb/s (standard ADSL) up to 448 kb/s (Max) and 832 kb/s (Premium Max).


IPstream Max is a ‘best efforts’ product, and thus no guarantee is given that increased data throughput will be experienced over that of the IPstream Office and Pro products. Where a customer upgrades from a fixed rate product to Max the speed their line achieves might be lower than they previously had.


The actual speed a line achieves is dependant upon:


  • Line length
  • Line quality
  • Electrical Interference


It is quite possible for two geographically close to have different line speeds.
IP throughout is dependant upon other factors such as server rate limiting. User will NOT be able to download files from the Internet at anywhere near 8Mbps.


Best speed
The best possible speed is determined by a service called Digital Line Management. This uses a variety of techniques to find the Maximum Stable Rate that a line can support.


(Minimum) 10 day Training period
To achieve the best possible speed when a line is first connected a new line undergoes a minimum 10 day training period to determine the Maximum Stable Rate. During this period line speed will vary and some disconnections will be experienced. This is correct behaviour and we are unable to log faults during this 10 day training period.


Digital Line Management contnually monitors line performance and adjusts speeds if necessary.

What throughput speeds can I expect on data circuits?

Please refer to our Service Level Agreement for the performance targets for the relevant services:

Spitfire SLAs

Streaming Issues? (e.g. Amazon Prime, Netflix etc)

In recent years many streaming providers (such as Amazon Prime, Netflix, BBC iPlayer, etc.) have changed their security measures to prevent content being accessed outside of the licensed region while others like NOW (Now TV) may not allow their content to be accessed outside of the UK at all.

As a result, some users may be blocked from using the services if the streaming provider suspects the IP address used is outside of the UK or that the user is using a VPN or proxy in an attempt to access regional content.

How do I know if this has happened to me?

• You may see an error within your application that informs you that “the IP address is outside of the UK” but you are, in fact, within the UK, or it may claim that you are using a VPN or proxy, or other similar message, when you believe you are not. You might even have been informed by your streaming provider to contact your Internet Service Provider (ISP) for assistance.

What can I do if this happens to me?

• Make sure you are using your Spitfire connection.

• If you are using a VPN or Proxy and are in the UK, disable it, clear your cache, and wait to see if it helps. This may take from less than an hour to a few days, or significantly longer. We regret to advise that is entirely outside Spitfire’s control.

• You can check where your IP address is registered by using an IP address checking website (type “What’s My IP Address” into your search engine for a number of web results that can confirm your IP address registered location). The IP address should be listed as “GB” or “UK”. If it is correctly listed, you will need to go back to your streaming provider and point out that the IP address is correctly listed.

What can I do to avoid this happening again in the future?

• Be careful to avoid using a VPN or proxy, or attempting to access your domestic UK services from abroad, where they are not permitted to be accessed outside the UK.

• Make sure your streaming provider username and password is updated and secure to avoid your account being compromised and used by unknown third parties without your knowledge.

• Ensure that access to your internet connection is restricted to trusted users and that all users know that using a VPN or proxy may result in them being blacklisted by the streaming providers (outside Spitfire’s control).

Do you provide static IP addresses?

Yes, we can provide fixed IP addresses that are dynamically allocated but consistently served (so you get the same IP address every time your router logs in). This is the most suitable option for businesses who need to run their own mail servers or set up VPNs between sites.

How to determine optimum MTU size

Maximum transmission unit (MTU) is a measurement in bytes of the largest data packets that an Internet-connected device can accept and can often cause problems with accessing and downloading from certain websites or FTP sites.

Finding the optimum size for your MTU will often resolve issues and give better overall performance.

Determining the optimum MTU size from a Windows Machine
From a Command Prompt type:

Ping –f –l 1500

-f means set the Do not Fragment bit in the TCP header
-l means fix the size of the packet in bytes
1500 sets the packet size to 1500

The destination host should be the one you are having trouble reaching, or a server on the other side of the VPN is you are having VPN problems.
Z:\>ping -f -l 1500

Pinging [] with 1500 bytes of data:

Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Reduce the size of the packets sent until a value is reached where packets are correctly returned:

Z:\>ping -f -l 1272

Pinging [] with 1272 bytes of data:

Reply from bytes=1272 time=103ms TTL=124
Reply from bytes=1272 time=103ms TTL=124
Reply from bytes=1272 time=103ms TTL=124
Reply from bytes=1272 time=103ms TTL=124

Ping statistics for
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 103ms, Maximum = 103ms, Average = 103ms

Here a packet size of 1272 works OK. To get the MTU value we need to add 28 bytes for the TCP header so we should set the MTU to be 1272 + 28 = 1300 bytes.


Connectivity Glossary


Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology.  Bandwidth (and bit rate) is greater toward the customer premises (known as downstream) than the reverse (known as upstream).


Broadband is a wide bandwidth data transmission with an ability to simultaneously transport multiple signals and traffic types. The medium can be coaxial cable, optical fibre, radio or twisted pair. 


Spitfire proprietary method of combining data circuits to provide a higher quality and resilient broadband service.


Ethernet Access Direct.  High quality Fibre circuit used to provide a Wide Area Network between two sites, for example between two main offices or between an office and a data centre hosting applications. 


Ethernet in the first mile. EFM or Copper Ethernet is a leased-line replacement service, delivered via multi copper pairs for added resilience. SLAs and guarantees on bandwidth and uptime apply. 


A ubiquitous layer 1/2 network protocol. Historically used for LAN connections it is now widely deployed for WAN connections giving symmetric, low latency connections between sites.


Fibre To The Cabinet.  Deploys fibre to a roadside cabinet and then copper cable to a customer premises. 


Generic Ethernet Access.  The UK’s best-value leased line service with speeds of up to 20Mb, with dedicated end-to-end bandwidth both up and downstream.

Leased Line

A widely used term for a private WAN circuit rented from a telecom provider rather than owned outright. A term still in common use for any WAN circuit.

Mbps & Gbps

Megabits and Gigabits per second.           


Optical Spectrum Access.  Point to point WAN connectivity between sites using different wavelengths of light over the same fibre.            

Point to Point 

Direct service linking two geographical sites, e.g. A end and B end.            


Providing alternative data paths in the event of single circuit failure. 

Router / Routing 

A device for forwarding data packets between networks. The process of forwarding data packets between networks. 


SDSL is Symmetric Digital Subscriber Line – providing the same upload and download speeds. 


Spitfire proprietary method of providing broadband service suitable for use with VoIP applications. 


VDSL – Very fast Digital Subscriber Line. Often referred to as fibre broadband.

IP Engineering Glossary



Common Gateway Interface. A Web server that supports CGI can be configured to interpret a URL that it serves as a reference to a CGI script. A common convention is to have a cgi-bin/ directory at the base of the directory tree and treat all executable files within this directory (and no other, for security) as CGI scripts.


CloudFlare is a Content Delivery Network (CDN) that allows your website to scale and cope with peaks in demand by automatically distributing your website from multiple servers all over the Internet and can offer your website DDoS protection and other advanced defences against website attacks.


The industry leading web GUI for managing your web space package. Everything you could possibly want to change and configure is all available from an easy to use GUI, with no knowledge of Linux required.

Domain / DNS    

Domain Name System converts logical names into IP addresses because humans remember names better than numbers.


Those in the know use Drupal to build everything from personal blogs to enterprise applications. Thousands of add-on modules and designs let you build any site you can imagine. Drupal is used to build websites for The White House, The Economist, The Prince Of Wales, The British Medical Journal and is even used on The Official Beatles website – so you will be in esteemed company.


Electronic Mail is information stored on a computer that is exchanged between two users over telecommunications. More plainly, e-mail is a message that may contain text, files, images, or other attachments sent through a network to a specified individual or group of individuals.

for PHP, Perl and Python             

PHP is a fast and powerful server-side scripting language designed especially for building complex websites that do exactly what you want them to do. It powers some of the biggest sites on the internet and sits behind the scenes of many web applications and content management systems. It powers almost 40% of all the websites on the web.


File Transfer Protocol.


The process of ensuring compatibility between hardware and software solutions.

IP Address

An IP address is a layer 3 address that identifies each computer or device using the Internet Protocol to communicate over a network.

IP Cortex             

IP – Internet Protocol.  IP Cortex is a specialist solution in Open, IP based call management systems for VoIP (Voice over Internet Protocol).

IPS Tag  

An IPS tag is a tag that was implemented by the UK registry (Nominet), to control domain name transfers. Every UK domain name (,,, etc.) must have a IPS tag specified to confirm which registrar currently holds the domain.

IPsec VPN           

IPsec is not a protocol in itself, but rather an umbrella term for a suite of protocols that, when combined, secure traffic at the IP layer to create VPNs (Virtual Private Network).


Joomla is an award-winning content management system (CMS), which enables you to build websites and powerful online applications.


Local Area Network. A network usually within a single building.


Multi-Protocol Label Switching. A method of switching data packets using labels assigned by the service provider network rather than addressing information in the layer 3 address. Often used as an alternate method of creating Virtual Private Networks (VPN) or Private Wide Area Networks (PWAN) for customers.


The number one open-source SQL database using Structured Query Language.


Post Office Protocol Version 3 and Internet Message Access Protocol email delivery systems. Two alternative protocols used for receiving email.

SIP Provider        

A SIP provider (Session Initiation Protocol) is any telecommunications company which provides SIP Trunking to customers, usually businesses. Normally they provide SIP “termination” (outbound calling) and “origination” (inbound calling).

Soft fax  

Soft Fax is the use of the Internet Protocol to send a fax (facsimile), rather than using only phone networks (traditional faxing) with a fax machine. Internet fax includes “web fax” and “email fax,” along with VoIP fax, which is the use of Voice over Internet Protocol to send a fax.


TAPI (Telephony Application Program Interface) is a standard program interface that lets you and your computer “talk” over telephones or video phones to people or phone-connected resources elsewhere in the world.


Voice over Internet Protocol.


Virtual Private LAN Service (VPLS) is a technology that provides Ethernet based multi-point to multi-point communication over IP/MPLS networks. It allows geographically dispersed sites to share an Ethernet broadcast domain by connecting sites through pseudo-wires.


Virtual Private Network


Wide Area Network. A data network joining geographically dispersed sites.

Website Hosting              

It is common for most websites to be run on a server with multiple internet connections using services provided by a website hosting company or an ISP.


WordPress is a publishing platform that allows anyone to make powerful, professional-looking websites quickly and easily. You can have your website and blog up and running in minutes, then customise it using thousands of free and paid for themes, widgets and plugins.


Voice Glossary

1U hardware 

1 rack unit – a system of measurement for equipment that is mounted in a standard 19 inch (wide) IT rack. 1U is equivalent to 1.75 inches. A typical rack will be 48 U high and manufacturers will state how high their equipment is in a U measurement. It ensures that a rack can be filled with different manufacturers devices because they conform to a standard measurement system. One of the few last bastions of the Imperial measurement system used throughout the World.

Analogue Lines

Direct Exchange Lines (DELs) for use with alarm, PDQ, ADSL or Fax

Call Diversion

Re-directing calls dialled to one destination to an alternative destination.

Converged Voice and Data

Carrying voice and data over the same circuit makes efficient use of available bandwidth

CPE Systems

Customer Premises Equipment – describing on-site telephone systems like Avaya IP 500 Office and 3CX.


Carrier Pre-Selection sends a customer’s calls to a telephony provider of their choice to route their calls to their destination.


Direct Dial In numbers (DDIs) are numbers that allow calls to bypass the operator and be directed straight to the required extension. They are normally used with a PBX (private branch exchange) telephone system, providing separate numbers for individuals, which is programmed to route incoming calls using DDI numbers to the correct extensions.

Geographical Numbers

A Geographic Telephone Numbers starts with an area code which is related to a geographic location in the UK.  Spitfire can provide numbers on every single UK telephone exchange.

Hosted PBX

A Hosted PBX is a private branch exchange (PBX) delivered as a hosted service rather than a piece of hardware on the customer’s site.

Hunt Groups

Hunt Groups refers to the method of distributing phone calls from a single telephone number to a group of several phone lines. Specifically, it is the process or algorithm used to select which line will receive the call. Hunt groups are supported by most PBX phone systems.

Intelligent Call Routing

Managed by a central portal, where you can set up, manage and change call diverts calls to your office in the day, your mobile in the evening, and a home office or answering service at the weekends which Works with 03 and 08 NTS numbers as well as standard geographic telephone numbers.

ISDN2e Lines

Integrated Services for Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.  It comes with two channels on one connection, enabling the use of broadband and calls at the same time, for smaller offices.


Integrated Services for Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.

NTS or Non Geographic Numbers

Number Translation Service.  These are 08 and 03 numbers giving a company a national presence regardless of location where calls can be routed through to an office line or any other ‘host number’.


A private automatic branch exchange (PABX) is an automatic telephone switching system within a private enterprise.


A PBX (private branch exchange) is a telephone system within an enterprise that switches calls between enterprise users on local lines while allowing all users to share a certain number of external phone lines.


Private Branch Exchange. A privately owned switch providing wired and possibly also wireless service.

Port / Porting

In the UK ranges of telephone numbers are assigned by Ofcom to different competing telephone companies. If a customer of one telephone company wished to move their telephone service to another they can normally ask for the numbers to be ported to their new provider. When this happens calls to the customer numbers are forwarded on from the number range holder to the new customer service provider’s network for onward call delivery.


Session Initiation Protocol.

SIP Communicator™

A multiple award winning Spitfire proprietary hosted PBX system.

SIP Trunks

SIP trunking is a Voice over Internet Protocol (VoIP) and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) provide breakout and break-in from the Public Switched Telephone Network (PSTN).

Switch / Switching

A generic term that could refer to an Ethernet switch that connects computers and devices together using the Ethernet protocol. When the term is used in a telephony network it could refer to a device or software that routes telephone calls.

Support Solutions Glossary

Auto Fail Over

Automatic transfer of backup services in the event of outages.


Customer Relationship Management.


Customer Relationship Management.


Quality of Service.


Service Level Agreements.

Phone Systems

User Guides

Firewall as a Service (FWaaS)

Our Network

Our fully resilient multi-node core network fibre ring now spans four geographically diverse locations: Telehouse – Docklands North, Equinix – Docklands South, The Oval in South London and Equinix LD3 in West London’s Park Royal.

This core network footprint also allows Spitfire to provide on-net access to other key UK data centres where our customers and partners want to connect to their services hosted elsewhere, as well as including multiple carrier connectivity options.