[Networkmanager] pppoe connection gets a secondary wrong IP address

[nmgr053 at iotti.biz]

Hi all

I'm trying for the first time to configure a pppoe NM connection via a DSL
bridge. The OS is a new Alma Linux 9 install. A similar connection, but made
in the older network-scripts way, did work until I reinstalled the box.

I simply added the connection with 
nmcli connection add con-name dsl-pppoe type pppoe ifname ens1 username
xxxxx password xxxxx connection.autoconnect yes

The connection is negotiated well, PPP/IPCP works, I get my static public IP
address. The problem is that strangely to me, NM configures the 1.0.0.0 on
the interface too. This becomes the preferred source address, so I can not
make connections from my machine to the outside. i.e.:

# ip a l dev ppp0
23: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc fq_codel
state UNKNOWN group default qlen 3
    link/ppp 
    inet 82.6.7.8 peer 192.168.100.1/32 scope global ppp0
       valid_lft forever preferred_lft forever
    inet 1.0.0.0 peer 82.6.7.8/32 scope global noprefixroute ppp0
       valid_lft forever preferred_lft forever

I don't understand where that inet 1.0.0.0 comes from.

I took a tcpdump of the IPCP config requests/ack and I obviously found my
real 82.6.7.8 IP address, but nothing about 1.0.0.0 .

I tried to debug NetworkManger activity. The trace is long, but the first
time 1.0.0.0 is encountered is in these lines:

Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <info>
[1697545591.4494] ppp-manager: (IPv4 Config Get) reply received.
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4495] ppp-mgr[53d9673f9f182516]: ip-config v4 received
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4495] ppp-mgr[53d9673f9f182516]: set state: have-ip-config (was
have-ifindex)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4496] ppp-mgr[53d9673f9f182516]: emit signal: state-changed,
state=have-ip-config, old-state=have-ifindex, ifindex=6, reason=ip config
received
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <debug>
[1697545591.4496] device[3e16a0d952df9134] (ens1): ip:dev4: set state=done
(has extra IP configuration)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4496] l3cfg[d04d98862e8219a9,ifindex=6]: IP configuration
changed (mark dirty)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <debug>
[1697545591.4496] device[3e16a0d952df9134] (ens1): ip:dev: set state=done
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4497] l3cfg[d04d98862e8219a9,ifindex=6]: commit update (auto)
(idle handler)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4497] l3cfg[d04d98862e8219a9,ifindex=6]: acd[1.0.0.0, init]:
track [l3cd=f1f7d2cce73884a0,obj=5af6210b199ad005,tag=5b29ed498c674a2b] with
timeout 0 msec, defend=a
l
ways (new)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4497] l3cfg[d04d98862e8219a9,ifindex=6]: acd[1.0.0.0, init]:
skip probing (acd disabled by configuration, during pre-check)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4497] l3cfg[d04d98862e8219a9,ifindex=6]: acd[1.0.0.0, ready]:
set state to ready
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <trace>
[1697545591.4498] l3cfg[d04d98862e8219a9,ifindex=6]: emit signal
(l3cd-changed, l3cd-old=[b28257230dabe9aa], l3cd-new=[789afffb6e0c2270],
commited=0)
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <debug>
[1697545591.4498] l3cfg[d04d98862e8219a9,ifindex=6]: obj-state: track:
[f9a6252a5cf48691, ip4-address, 1.0.0.0/32 lft forever pref forever lifetime
13-0[0,0] ptp 82.6.7.8
 dev 6 src ppp]
 dev 6 src ipv6ll force-commit]
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <debug>
[1697545591.4499] l3cfg[d04d98862e8219a9,ifindex=6]: obj-state: track:
[4d883f1f322f5db8, ip4-route, type unicast 0.0.0.0/0 via 82.6.7.8 dev 6
metric 103 mss 0 rt-src ppp
]
Oct 17 14:26:31 test.domain.com NetworkManager[1254]: <debug>
[1697545591.4499] l3cfg[d04d98862e8219a9,ifindex=6]: obj-state: track:
[d75462eea012f585, ip4-route, type unicast 82.6.7.8/32 dev 6 metric 103 mss
0 rt-src rt-kernel scop
e link pref-src 1.0.0.0]

Any hint where this 1.0.0.0 address could come from?

I can mitigate the problem by manually deleting the address with ip a del
1.0.0.0 dev ppp0 , but I would be curious to understand what's going on.

Thank you in advance:)