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Npcap loopback adapter not showing in Windows > Network Connections

asked 2020-11-10 11:20:47 +0000

DavidA_2018 gravatar image

updated 2020-11-11 08:26:03 +0000

grahamb gravatar image

Hi,

I am running Windows 10 1903 and have installed Wireshark 3.4.0 (without npcap) followed by an install of npcap 1.00.

Wireshark shows interface 'Adaptor for loopback traffic capture', which I assume is npcap, but that interface does not appear in Control Panel > Network Connections, so I cannot set the IP address.

Am I correct that the npcap interface should appear in Control Panel?

If so, why might it not appear?

I am unable to upload a file, so I have pasted in part of the npcap diagnostic report below.

Best regards David

*************************************************
Network Adapter(s) Info:
************************************************

Caption             : [00000003] Intel(R) Ethernet Connection (4) I219-V
GUID                : {43FF34BD-ADC5-4463-A2AA-AD27BAAE0733}
Index               : 3
InterfaceIndex      : 11
Manufacturer        : Intel
MACAddress          : C8:D9:D2:DF:D8:60
Speed               : 9223372036854775807
NetConnectionID     : Ethernet
NetConnectionStatus : 7
PNPDeviceID         : PCI\VEN_8086&DEV_15D8&SUBSYS_83B2103C&REV_21\3&11583659&0&FE
ServiceName         : e1dexpress
AdapterType         : Ethernet 802.3

Caption             : [00000004] Intel(R) Dual Band Wireless-AC 8265
GUID                : {2EEBFF1D-E0FE-40F5-A8A2-47CB862E4138}
Index               : 4
InterfaceIndex      : 9
Manufacturer        : Intel Corporation
MACAddress          : 30:24:32:DA:1B:5A
Speed               : 650000000
NetConnectionID     : Wi-Fi
NetConnectionStatus : 2
PNPDeviceID         : PCI\VEN_8086&DEV_24FD&SUBSYS_10108086&REV_78\4&179899FD&0&00E0
ServiceName         : Netwtw06
AdapterType         : Ethernet 802.3

Caption             : [00000005] Bluetooth Device (Personal Area Network)
GUID                : {741142D7-1AA0-4A5C-9C58-3E099DBB6FA0}
Index               : 5
InterfaceIndex      : 15
Manufacturer        : Microsoft
MACAddress          : 30:24:32:DA:1B:5E
Speed               : 3000000
NetConnectionID     : Bluetooth Network Connection
NetConnectionStatus : 7
PNPDeviceID         : BTH\MS_BTHPAN\6&2620B7E7&0&2
ServiceName         : BthPan
AdapterType         : Ethernet 802.3

Caption             : [00000017] Juniper Networks Virtual Adapter
GUID                : {CEE541B4-AD66-4983-8D88-31B361A28DC2}
Index               : 17
InterfaceIndex      : 23
Manufacturer        : Juniper Networks
MACAddress          : 02:05:85:7F:EB:80
Speed               : 2000000000
NetConnectionID     : Local Area Connection* 12
NetConnectionStatus : 2
PNPDeviceID         : {FE36527A-8C07-4854-8AF7-BF40E7DF52F7}\JNPRVA\0001
ServiceName         : jnprva
AdapterType         : Ethernet 802.3

Caption             : [00000019] Hyper-V Virtual Ethernet Adapter
GUID                : {BB7F4183-A50D-4564-9FF8-2D673F6AC80C}
Index               : 19
InterfaceIndex      : 19
Manufacturer        : Microsoft
MACAddress          : 00:15:5D:4E:6A:28
Speed               : 10000000000
NetConnectionID     : vEthernet (WSL)
NetConnectionStatus : 2
PNPDeviceID         : ROOT\VMS_MP\0000
ServiceName         : VMSNPXYMP
AdapterType         : Ethernet 802.3
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Comments

It does not appear in the CP. Why do you want to set an IP address, it's implicit as the loopback adaptor; 127.0.0.1 and ::1?

grahamb gravatar imagegrahamb ( 2020-11-10 11:45:08 +0000 )edit

Thanks, I'll try 127.0.0.1. However, I'm sure I used to be able to set it in CP.

DavidA_2018 gravatar imageDavidA_2018 ( 2020-11-10 17:46:50 +0000 )edit

Note that all local machine traffic can be captured on the loopback adaptor, e.g. if you send to a local IP then that will show up because the Windows stack will short-circuit it and not actually put it on the wire.

Maybe you could explain what you want to do rather than how you think you can do it?

grahamb gravatar imagegrahamb ( 2020-11-10 18:11:37 +0000 )edit

1 Answer

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answered 2020-11-11 02:07:16 +0000

Guy Harris gravatar image

You're assuming the loopback adapter is a regular Windows network adapter that can have an IP address assigned to it, and that loopback traffic passes through it.

As far as I know, that's not the case. Windows support loopback traffic to 127.0.0.1 even if you don't have Npcap installed; the looping back doesn't go through a regular NDIS interface, I think it's special-cased in the IPv4 and IPv6 code.

All Npcap does is provide a special hook to allow that looped-back traffic to be captured; the hook looks like a network adapter from the point of view of the libpcap API, so that programs using that API (which is also the Npcap API) to capture traffic can capture on it the same way it can capture on a regular interface, but that doesn't mean it is a regular interface.

If you want an authoritative answer, you should post it as an issue on the Npcap issues list, so that Daniel Miller, the Npcap developer, can answer in more detail. My main role in Npcap is "developer and maintainer of the code in libpcap that uses the lower-level Npcap code, and that's incorporated into Npcap"; I do know some of Npcap's lower-level innards, but I don't regularly work on it, I just look at it as necessary to make libpcap stuff work with it.

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Asked: 2020-11-10 11:20:47 +0000

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Last updated: Nov 11