MikroTik

We're working with a small ISP which is connected to a Tier 1 provider. They have probably 2,000 subscribers. Recently, they've asked us to review their eBGP and iBGP configurations because they suspect it's running inefficiently. They're receiving 2+ million routes from their Tier 1 provider.

My question is, can't we just sum this into a single default route? Does receiving this 2+ million routes give us flexibility if they were to load balance between a primary and secondary Tier 1/2 provider?

Why a single BGP session is providing 2 million routes is concerning - biggest full table I have across sites is just under 1 million, so it seems high.

But - if they do not have multiple providers, only one external provider, then generally a default route is a much more efficient way to do things. Taking in full tables can help if you are using multiple providers, and mostly are trying to find best path for outbound traffic.

You need to go with default route only, if you have only one bgp peer to your upstream provider.
And yes full internet routing table is less then 1 milion prefixes

Thank you for your explanations. This all makes sense.
They have two peers, so we're going to do some investigating as to see whether we need to cut down on redundant routes in some way; but the 2 million+ routes isn't as bad as I first figured.