If you have mission-critical dependency on your Wide Area Network (WAN) connectivity, you have to understand what ISP SLAs (Service Level Agreements) really mean for you and if they can keep your Internet up and running.
In most cases, your ISP (Internet Service Provider) will promise SLAs which sound great but are usually merely sales pitches to tie you up with a long-term contract. If you look at the fine print, you will notice that the penalty for the ISP not meeting their SLAs is usually proportional to the cost of their service for the duration of the outage. So, a full day of Internet downtime may really mean only 1/30th of the monthly Internet cost will be credited to your account by your ISP, even though it may have cost you thousands of dollars. In my book, this is not how you build in a penalty for the ISP to keep your business Internet up and running at all costs. (I want to note here that some large integrators and value-added resellers would gladly step in and fill this void by taking on the risk of a true ISP SLA with high penalties. However, usually that risk has an associated high cost built into the service package, so may not be applicable for your business as an option).
If you want to achieve high 9s availability and very high Internet reliability, you have to put your eggs into different baskets. This means getting connectivity solutions from different ISPs, ideally with completely different infrastructures. This way, you are protecting your network against some correlated downtimes such as a telco Central Office (CO) being down, or an ISP’s backhaul routing being unavailable because of a BGP update. So ideally, you want to bring in various types of Internet access lines into your office and build a simple redundancy scheme to create a highly reliable WAN connectivity for your business, i.e. build your own ISP SLA.
The simplest redundancy you can build is literally having a manual failover mechanism with the additional spare Internet line. For example, if you have a T1 or MPLS connection at your office as your primary Internet line, you may want to keep an inexpensive DSL or cable connection at the office so that you can manually switch over your WAN connection within a few minutes of the outage. Not ideal, but works at a certain level.
The second, and more sophisticated approach, would be to have a load-balancing router do the manual switching for you. This will provide you with reliable failover in a relatively quick time frame, although would lack the latest features such as keeping the ongoing Internet sessions alive (in essence, you will need to re-initiate your VPN connection) if your primary line failed.
The third and the latest technology, would be to use Internet bonding routers to keep all your available WAN resources active and in use at all times. Priced similarly to load-balancing routers, these boxes will provide your office not only the additional bandwidth and speed, but also dynamic failover and session continuity features. This means the loss of any of the WAN links can be shielded from the applications, allowing your upload of a file to continue, or maintaining crystal-clear VoIP calls, if any of your WAN links carrying that traffic goes down. So the only way you will realize that your primary Internet connection went down would be the email alert that your Internet bonding router will send you or the syslog entry populated by the broadband bonding router.
Cahit Akin, CEO, Mushroom Networks, Inc.
Mushroom Networks is the provider of SD-WAN (Software Defined WAN) and NFV solutions capable of Broadband Bonding that enables self-healing WAN networks that route around network problems such as latency, jitter and packet loss.