Enable Matrix Federation on same Cludron server

[andreasdueren]

I'd like to propose a change to the default synapse config file. Currently, the federation blacklist blocks any connections from another Matrix instance on the same server:

federation_ip_range_blacklist:
  - '127.0.0.0/8'
  - '10.0.0.0/8'
  - '172.16.0.0/12' # this is blocking the internal conections
  - '192.168.0.0/16'
  - '100.64.0.0/10'
  - '169.254.0.0/16'
  - '::1/128'
  - 'fe80::/64'
  - 'fc00::/7'

Synapse supports additional whitelisting which overrides the blacklist:

ip_range_whitelist:
  - '172.18.0.0/16' # Whitelist the Cloudron's docker network

[girish]

Cloudron's docker network is in 172.18.0.0/16 which afaict is not in the federation_ip_range_blacklist . What am I missing?