If you are hosting your site with a shared, VPS, dedicated, or cloud web hosting provider. There is a 99% + chance they have multiple upstream providers. These upstream providers can be their colocation provider, datacenter providers, company they are leasing servers from, equipment vendors, IP transit carriers, and many other companies that your web host has to work with. The most important ones you should know are who your web host’s bandwidth carriers or IP transit carriers are.
Who is providing your web host with their internet connection is something that is important. You need to know this and who these providers are may change over time. Bandwidth carriers or IP transit carriers are the internet service providers that provide the actual fiber connections to your web host’s datacenter.
Single homed networks
No matter how large or small your web host is or how well their perceived reputation to be. Their reputation can be known as a great web hosting provider with top notch customer service. This means nothing if they have one single network connection to the internet. With one network connection this does not necessary mean one physical connection but means your web host’s network relies upon one single IP transit upstream provider to provide network access to the internet. If there were any network routing or any other issues no matter how many physical fiber connections your web host has to their IP transit upstream provider. The network routing or other issue could mean traffic issues would be encountered when attempting to access site hosted with your web host.
Two IP transit upstream providers
Having 2 IP transit upstream providers is an improvement over having a single homed network. This improvement is not much but lessens the chance and risks when one of the IP transit upstream provider may have any issues. Having 2 IP transit carrier helps to broaden the different paths that traffic may your sites from the internet. If one of the two IP transit carriers were to encounter any issues and the remaining IP transit carrier doesn’t have the capacity to handle the unexpected surge in traffic. Your sites would probably be not accessible for a few hours while your web host works to fix it. Having 2 IP transit carriers but if the distribution and capacity of the two are dramatically different then any shift in traffic pattern may knock your web host offline.
Three or more IP transit carriers is better
The most optimal network setup involves having multiple if not dozens and dozens of IP transit carriers. The more ISPs your web host are connected to the better. This lessens the chance that any network congestion or routing issue would have on your sites. The more connections your web host has, the more diverse, and multiple paths would be available for visitors to use to access your sites.
Quality IP transit carriers versus low quality IP transit carriers
If your web host has more than 3 IP transit carriers but if each of these IP transit carrier are low quality (single homed or only have 2-3 upstream connections themselves) than all 3 IP transit carrier would save your web host a lot of money but there would be more risks for you if any network congestion or issues were to arise.
This is why you must inquire and know who your web host’s upstream IP transit carriers are. If your web host refuses to say or is outright concealing this information than your web host is putting your sites at risk so they can save money by using low quality IP transit carriers.