Hello Nik,
I'll try to explane you the complete situation.
Here is the content of the Plesk page IP Addresses (/admin/ip-address/list/):
IP address Interface IP type Resellers Sites
213.32.108.231 /255.255.255.255 "Ethernet" Shared 2 120
5.39.73.187 /255.0.0.0 "Ethernet" dedicated 0 0
54.36.11.94 /255.255.255.255 "Ethernet" Shared 1 1
The main IP of the server, assigned by the farm is 5.39.73.187.
Here are the commands you required when sites are unreacheable:
C:\>ipconfig /all
Windows IP Configuration
Host Name . . . . . . . . . . . . : ******
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Ethernet:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) I210 Gigabit Network Connection
Physical Address. . . . . . . . . : A4-BF-01-44-48-A1
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::f15d:7bba:f67b:b00d%4(Preferred)
IPv4 Address. . . . . . . . . . . : 5.39.73.187(Preferred)
Subnet Mask . . . . . . . . . . . : 255.0.0.0
IPv4 Address. . . . . . . . . . . : 54.36.11.94(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.255
IPv4 Address. . . . . . . . . . . : 213.32.108.231(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . : 5.39.73.254
DHCPv6 IAID . . . . . . . . . . . : 61128449
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-24-AE-AE-42-A4-BF-01-44-48-A1
DNS Servers . . . . . . . . . . . : 213.186.33.99
NetBIOS over Tcpip. . . . . . . . : Enabled
Tunnel adapter isatap.{3A6E91E8-E82A-4AE4-9506-45644F98372C}:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Tunnel adapter Teredo Tunneling Pseudo-Interface:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv6 Address. . . . . . . . . . . : 2001:0:2851:782c:24b8:a02:fad8:b644(Preferred)
Link-local IPv6 Address . . . . . : fe80::24b8:a02:fad8:b644%2(Preferred)
Default Gateway . . . . . . . . . : ::
DHCPv6 IAID . . . . . . . . . . . : 167772160
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-24-AE-AE-42-A4-BF-01-44-48-A1
NetBIOS over Tcpip. . . . . . . . : Disabled
C:\>route print
===========================================================================
Interface List
4...a4 bf 01 44 48 a1 ......Intel(R) I210 Gigabit Network Connection
1...........................Software Loopback Interface 1
3...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter
2...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface
===========================================================================
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 5.39.73.254 5.39.73.187 281
5.0.0.0 255.0.0.0 On-link 5.39.73.187 281
5.39.73.187 255.255.255.255 On-link 5.39.73.187 281
5.255.255.255 255.255.255.255 On-link 5.39.73.187 281
54.36.11.94 255.255.255.255 On-link 5.39.73.187 281
127.0.0.0 255.0.0.0 On-link 127.0.0.1 331
127.0.0.1 255.255.255.255 On-link 127.0.0.1 331
127.255.255.255 255.255.255.255 On-link 127.0.0.1 331
213.32.108.231 255.255.255.255 On-link 5.39.73.187 281
224.0.0.0 240.0.0.0 On-link 127.0.0.1 331
224.0.0.0 240.0.0.0 On-link 5.39.73.187 281
255.255.255.255 255.255.255.255 On-link 127.0.0.1 331
255.255.255.255 255.255.255.255 On-link 5.39.73.187 281
===========================================================================
Persistent Routes:
Network Address Netmask Gateway Address Metric
0.0.0.0 0.0.0.0 5.39.73.254 Default
===========================================================================
IPv6 Route Table
===========================================================================
Active Routes:
If Metric Network Destination Gateway
2 331 ::/0 On-link
1 331 ::1/128 On-link
2 331 2001::/32 On-link
2 331 2001:0:2851:782c:24b8:a02:fad8:b644/128
On-link
4 281 fe80::/64 On-link
2 331 fe80::/64 On-link
2 331 fe80::24b8:a02:fad8:b644/128
On-link
4 281 fe80::f15d:7bba:f67b:b00d/128
On-link
1 331 ff00::/8 On-link
4 281 ff00::/8 On-link
2 331 ff00::/8 On-link
===========================================================================
Persistent Routes:
None
>>>is your server available by alias ip (not by hosted domain name) when such circumstances happen ?
No, if I ping the alias IP 213.32.108.231 from a Vodafone connection I get all the packets lost
>>>have you checked is alias present in IIS > domain > bindings (for couple hosted domains that are unreachable) ?
Here is a screenshot
I bought a Vodafone SIM in order to do the tests because obviously I can't ask my clients to do them...
I'm not secure about all connections but it seems that mainly mobile connections are affected, I know about Vodafone Italy, Ho Mobile (sub of Vodafone) and a Hetzner server's IP of a client of mine.
Most other connections, especially land-lines ones, appear to be working normally.
Thanks for your help