Might be worth to consider running a software router on that scale with perhaps some cheap quad-port GbE PCIe NICs. BIRD would be the BGP daemon to go, or FRRouting if you want an integrated shell. Hardware routers for 100 Mbit egress seem a bit overpowered, however, as scaleable you want to go, some Ubiquiti routers might be a cheap option.

As for transit, have you considered a redundant tunnel-based solution instead? You can run that transparently on top of your RCN connection, with negligible costs for your commit and no additional connection fees.

On Sep. 3 2019, at 6:17 pm, ADNS NetBSD List Subscriber <nanog2@adns.net> wrote:
I have a need for a BGP enabled connection in the River North section of Chicago. We have a small number of IP blocks that we want to use. Currently, we have some equipment at 350 E. Cermak (Steadfast Networks) and are looking at downsizing and bringing stuff
in-house. Our bandwidth requirements are miniscule (10MB/Sec is fine).
 
I know RCN offers business cable-modem service but probably not BGP.
 
Also, we’d like to ditch our 3640 router in favor of a smaller “desktop” size router, but none of them seem to do BGP (not surprising).  Any recommendations on hardware would be welcome as well
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