Whenever your network is down, be it due to a technical problem or a DDOS-attack, the first thing you need to do is get your ‘emergency vehicles’ at the scene and assess the situation. But how to get them there if the main road is blocked, in this case with packets? Well, you use the service road.
A network can go down anytime and it can happen to anyone, as we have seen with Delta Airlines last week. When their network went down, it had its effect on the entire world, with over 700 flights being cancelled.
As a network manager, you want to get access to the network as quickly as possible, much like the police wants to get to an accident on the highway as quickly as possible. But the trouble is; traffic is blocking the police. So they want to use a service road. It is not as quick as the regular highway would normally be, but for now it is way faster.
In the case of networks, the service road is the ‘out of band management network’. This is basically an independent network that runs parallel to your production network. It can be as small as a 4 Mbps DSL line that runs the out of band management network, so it has the speed of a car on a dirt road. But when your main network is down, you will want to use it to get as quickly as possible to the problem.
The out of band management network can be used no matter what the reason is for your network problems. Whether it is a software bug causing problems with your BGP session, or whether it is deliberate, like with a DDOS-attack. Sure, during such an attack you could still reach your network devices through the normal channels, but it is borderline slow and it takes forever to send one command to your router’s CLI.
Chances are that the out of band management network is almost never used. That is why it is mostly a small band connection. But you want to have it – and be able to get to the problem when it really matters.