Hi,
In general, it is possible to use multiple internet connections to achieve load sharing. However, how exactly it should be done depends very much on how these multiple broadband connections are terminated at your premises. In your case, do you have all 5 broadband connections terminated on the same physical router, or are you using multiple routers to terminate these broadband connections?
If you have just a single router that handles all 5 broadband connections at once, you do not need to use HSRP/VRRP/GLBP, as the traffic going to the internet has to go through your single router anyway. It is then just a matter of proper configuration of your router to utilize multiple uplinks to the internet. There may be challenges with setting the NAT right, though.
If you have multiple routers with each of them handling just one or just a few broadband connections, you would then want to use one of the first hop redundancy protocols to achieve load sharing across multiple physical gateways. The ideal choice would be GLBP as it would allow using up to 4 active gateways. With HSRP or VRRP, you would have only a single active gateway, with the rest of the gateways being in standby mode, waiting to replace the active gateway but not being active at the same time. There are tricks such as mHSRP where you can create multiple virtual routers on the same network, assign them with different IP addresses, and have your PCs use different gateways, but that complicates the setup of both the routers and the end hosts.
Even with GLBP, it might be necessary to tweak the algorithm by which a certain host is assigned its gateway. Considering that each one of your routers would be performing its own independent NAT, it would be ideal for one host to use just a single gateway all the time so that from outside, it only has a single public IP address.
Regardless of the actual solution - either a single router handling all 5 broadband connections, or 5 standalone routers handling a single broadband connection each - you have to take into account that each host will be utilizing only a single broadband connection for a given conversation. The actual increase in the bandwidth will be visible only with multiple hosts communicating at the same time, as their total traffic will be spread over different uplinks. It is very similar to the way EtherChannel operates - a single traffic flow will not experience any speedup, as it will still be carried over a single link only. It is only multiple flows that are spread across different uplinks when they start experiencing the gain of the added bandwidth on additional uplinks.
So much for the general answer. If you would like us to guide you further, please try to explain your network in more detail. Ideally, post a diagram showing your network and the placement of your gateways, their type and IOS version. This will help us understand the environment in which you want to operate.
Best regards,
Peter
