Problema de gateway - "ping" funciona, "curl" não

Temos um servidor [S]SRV_GATEWAY com dois NICs ( [I]WAN/INT_LAN e [I]PRIV_LAN ) configurados como GATEWAY, DNS e DHCP para uma rede privada ( [N]PRIV_LAN ).

O servidor [S]SRV_GATEWAY acessa a internet (consome-se como DNS) e todos os outros servidores ( [S]PRIV_SRV_X ) consomem o DHCP, DNS e GATEWAY fornecidos pelo servidor [S]SRV_GATEWAY .

• Disposição da rede...

                     [N]WAN/INT_LAN (10.2.0.0/24)
                      ↕
                     [I]WAN/INT_LAN
                  [S]SRV_GATEWAY
                     [I]PRIV_LAN
                      ↕
                     [N]PRIV_LAN (10.3.0.0/24)
                      ↕
       ...............................
       ↕              ↕              ↕
      [S]PRIV_SRV_0  [S]PRIV_SRV_1  [S]PRIV_SRV_0
                     [S]PRIV_SRV_2  [S]PRIV_SRV_0
                     [S]PRIV_SRV_3
    
     _ [N] - Network;
     _ [I] - Network Interface;
     _ [S] - Server.
    
     _ [N]WAN/INT_LAN - Has internet access;
     _ [N]PRIV_LAN - Private network.

PERGUNTA: Por que podemos pingservidores com sucesso na internet e não podemos acessar os mesmos servidores usando curlo servidor [S]PRIV_SRV_0 (veja a saída abaixo)?

    [root@okd4-bootstrap core]# ping -c 2 www.google.com
    PING www.google.com (172.217.18.196) 56(84) bytes of data.
    64 bytes from ham02s14-in-f196.1e100.net (172.217.18.196): icmp_seq=1 ttl=113 time=10.5 ms
    64 bytes from par10s38-in-f4.1e100.net (172.217.18.196): icmp_seq=2 ttl=113 time=10.6 ms
    
    --- www.google.com ping statistics ---
    2 packets transmitted, 2 received, 0% packet loss, time 1001ms
    rtt min/avg/max/mdev = 10.500/10.548/10.597/0.048 ms

    [root@okd4-bootstrap core]# curl http://www.google.com
    curl: (7) Failed to connect to www.google.com port 80: No route to host

EXTRA:

• Como SRV_GATEWAY foi definido como GATEWAY:

O servidor SRV_GATEWAY foi configurado como GATEWAY através de comandos...

Ativar encaminhamento de IP ...

tee "/etc/sysctl.d/ip_forward.conf" << EOF
net.ipv4.ip_forward=1
EOF
sysctl -w net.ipv4.ip_forward=1

Configure um gateway NAT de saída com destino nos dispositivos de mascaramento NIC ens3 ( [I]WAN/INT_LAN ) configurados no CIDR 10.3.0.0/24...

firewall-cmd --permanent --direct --passthrough ipv4 -t nat -I POSTROUTING -o ens3 -j MASQUERADE -s 10.3.0.0/24
firewall-cmd --reload

• Algumas informações obtidas do servidor [S]PRIV_SRV_0 :

[root@okd4-bootstrap core]# cat /etc/resolv.conf | grep -i '^nameserver' | head -n1 | cut -d ' ' -f2
10.3.0.14

[root@okd4-bootstrap core]# ip r
default via 10.3.0.14 dev ens3 proto dhcp metric 100 
10.3.0.0/24 dev ens3 proto kernel scope link src 10.3.0.4 metric 100 

[root@okd4-bootstrap core]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.3.0.14       0.0.0.0         UG    100    0        0 ens3
10.3.0.0        0.0.0.0         255.255.255.0   U     100    0        0 ens3

[root@okd4-bootstrap core]# netstat -r -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         10.3.0.14       0.0.0.0         UG        0 0          0 ens3
10.3.0.0        0.0.0.0         255.255.255.0   U         0 0          0 ens3

[root@okd4-bootstrap core]# ping -c 2 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=113 time=10.8 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=113 time=11.0 ms

--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 10.769/10.891/11.013/0.122 ms

[root@okd4-bootstrap core]# cat /etc/resolv.conf
# This is /run/systemd/resolve/resolv.conf managed by man:systemd-resolved(8).
# Do not edit.
#
# This file might be symlinked as /etc/resolv.conf. If you're looking at
# /etc/resolv.conf and seeing this text, you have followed the symlink.
#
# This is a dynamic resolv.conf file for connecting local clients directly to
# all known uplink DNS servers. This file lists all configured search domains.
#
# Third party programs should typically not access this file directly, but only
# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a
# different way, replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

nameserver 10.3.0.14
search okd.local

[root@okd4-bootstrap core]# tracepath 8.8.8.8
 1?: [LOCALHOST]                      pmtu 1500
 1:  api-int.mbr.okd.local                                 0.526ms 
 1:  api-int.mbr.okd.local                                 0.855ms 
 2:  okd4-services.okd.local                               1.842ms !H
     Resume: pmtu 1500 

[root@okd4-bootstrap core]# tracepath www.google.com
 1?: [LOCALHOST]                      pmtu 1500
 1:  api.mbr.okd.local                                     0.481ms 
 1:  api-int.mbr.okd.local                                 0.562ms 
 2:  api.mbr.okd.local                                     0.553ms !H
     Resume: pmtu 1500 

[root@okd4-bootstrap core]# ip route show
default via 10.3.0.14 dev ens3 proto dhcp metric 100 
10.3.0.0/24 dev ens3 proto kernel scope link src 10.3.0.4 metric 100 

[root@okd4-bootstrap core]# nslookup www.google.com
Server:         10.3.0.14
Address:        10.3.0.14#53

Non-authoritative answer:
Name:   www.google.com
Address: 172.217.18.196
Name:   www.google.com
Address: 2a00:1450:4007:805::2004

[root@okd4-bootstrap core]# cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

Obrigado! =D