The cephadm MGR service is hosting different modules, like the Ceph Dashboard and the cephadm manager module.
The MGR service supports binding only to a specific IP within a network.
example spec file (leveraging a default placement):
service_type: mgr networks: - 126.96.36.199/24
Allow co-location of MGR daemons
In deployment scenarios with just a single host, cephadm still needs
to deploy at least two MGR daemons in order to allow an automated
upgrade of the cluster. See
the ceph-mgr administrator’s guide for further details.
See also: Co-location of daemons.