There are some specific edge-cases when is a need to run FRR and another FRR
and/or another BGP implementation on the same box. Relaxing 127.0.0.0/8 for
this case might be reasonable.
An example below peering via 127.0.0.0/8 between FRR and GoBGP:
% grep 127.0.0.2 /etc/frr/daemons
bgpd_options=" -A 127.0.0.1 -l 127.0.0.2"
% grep local /etc/gobgp/config.toml
local-address-list = ["127.0.0.1"]
donatas-pc# sh ip bgp summary
IPv4 Unicast Summary (VRF default):
BGP router identifier 192.168.10.17, local AS number 65001 vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 725 KiB of memory