Equal-cost multi-path routing (ECMP)

Hello,

Design question:

I currently have a BSD device acting as a router/firewall providing our connectivity.
This server runs BGP via OpenBGPD to advertise our resources allocated by LACNIC:

  • Our own ASN
  • One IPv4 /22 block
  • One IPv6 /48 block

I currently have Connection #1:

Speed: 1000 Mbps download / 500 Mbps upload
Characteristics: 1:4 contention/reuse ratio (marketed as "Broadband Internet")

I will soon add a Connection #2 from the same ISP (I know it's not ideal for true HA, but it's my only option):

Speed: 500 Mbps download / 500 Mbps upload
Characteristics: 1:1 no contention/reuse (marketed as "Dedicated Internet")

My questions:

  1. As I understand it, traditional ECMP via BGP works best when paths are symmetrical (same speeds and characteristics, e.g., two 500/500 1:1 links, or two 1000/500 1:4 links). Is that strictly required?
  2. Is it technically viable or recommended to implement ECMP with two such asymmetrical connections?

Has anyone here had experience with this kind of setup on FreeBSD?

Thanks in advance for your insights!
 
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