Comment 5 for bug 1861277

This is breaking at least the nrpe charm for fan networking, likely more if they use a similar mechanism:

On the Nagios host:
$ juju run --unit nagios/0 'network-get public'
bind-addresses:
- macaddress: fa:16:3e:01:32:39
  interfacename: ens2
  addresses:
  - hostname: ""
    address: 10.48.131.32
    cidr: 10.48.128.0/17
  - hostname: ""
    address: 10.48.131.32
    cidr: 10.48.128.0/17
- macaddress: ae:81:9a:5c:80:ed
  interfacename: fan-252
  addresses:
  - hostname: ""
    address: 252.6.64.1
    cidr: 252.0.0.0/8
egress-subnets:
- 10.48.131.32/32
ingress-addresses:
- 10.48.131.32
- 10.48.131.32
- 252.6.64.1

Relation data from the nrpe unit:
$ u=nrpe/6; r=monitors ; juju run --unit $u "relation-ids $r| xargs -I_@ sh -c 'relation-list -r _@|xargs -I_U sh -c \"relation-get -r _@ - _U |sed s,^,_U:, 2>&1\"'"
nagios/0:egress-subnets: 10.48.131.32/32
nagios/0:ingress-address: 10.48.131.32
nagios/0:private-address: 10.48.131.32

If the egress-subnets included the fanout address as well, nrpe would pick it up and add it to the config file. Both addresses can be used for egress.