Cannot enable Promiscuous Mode for network device

felix.specht@iosb-ina.fraunhofer.de

Hello,

i would like to enable the promiscuous mode for the 'eth0' network device.

 

I tried this with the following commands:

1) ip link set eth0 promisc on

2) ifconfig eth0 promisc

 

Verificiation via ip a shows it is not set.

 

After reboot of the system a log message via dmesg shows device eth0 entered promiscuous mode, but it is still not activated for the device. 

 

Is there any way to activate the mode?

Version is 2019.9

 

Best regards,

fspecht

Martin [PLCnext Technology Team]

Hi fspecht,

I am not sure how to check for certain that the interface is in promiscuous mode ...  but perhaps it is?

Here is what I tried:

admin@axcf2152:~$ su
Password: 
root@axcf2152:/opt/plcnext/# ip a
1: lo:  mtu 65536 qdisc noqueue qlen 1000
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
 valid_lft forever preferred_lft forever
 inet6 ::1/128 scope host 
 valid_lft forever preferred_lft forever
2: eth0: <<span style="background-color: #ffff00;">BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000
 link/ether 00:a0:45:9c:a1:13 brd ff:ff:ff:ff:ff:ff
 inet 192.168.178.221/24 brd 192.168.178.255 scope global eth0
 valid_lft forever preferred_lft forever
 inet6 fe80::2a0:45ff:fe9c:a113/64 scope link 
 valid_lft forever preferred_lft forever
3: sit0@NONE>:  mtu 1480 qdisc noop qlen 1000
 link/sit 0.0.0.0 brd 0.0.0.0
4: docker0:  mtu 1500 qdisc noqueue 
 link/ether 02:42:ec:9d:25:76 brd ff:ff:ff:ff:ff:ff
 inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
 valid_lft forever preferred_lft forever
root@axcf2152:/opt/plcnext/# 
root@axcf2152:/opt/plcnext/# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:A0:45:9C:A1:13 
 inet addr:192.168.178.221 Bcast:192.168.178.255 Mask:255.255.255.0
 inet6 addr: fe80::2a0:45ff:fe9c:a113/64 Scope:Link
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:12102 errors:0 dropped:38 overruns:0 frame:0
 TX packets:2344 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000 
 RX bytes:1225350 (1.1 MiB) TX bytes:329862 (322.1 KiB)
 Interrupt:29 Base address:0xe000

root@axcf2152:/opt/plcnext/# ifconfig eth0 promisc
root@axcf2152:/opt/plcnext/# ip a
1: lo:  mtu 65536 qdisc noqueue qlen 1000
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
 valid_lft forever preferred_lft forever
 inet6 ::1/128 scope host 
 valid_lft forever preferred_lft forever
2: eth0: <<span style="background-color: #ffff00;">BROADCAST,MULTICAST,UP,LOWER_UP100> mtu 1500 qdisc mq qlen 1000
 link/ether 00:a0:45:9c:a1:13 brd ff:ff:ff:ff:ff:ff
 inet 192.168.178.221/24 brd 192.168.178.255 scope global eth0
 valid_lft forever preferred_lft forever
 inet6 fe80::2a0:45ff:fe9c:a113/64 scope link 
 valid_lft forever preferred_lft forever
3: sit0@NONE>:  mtu 1480 qdisc noop qlen 1000
 link/sit 0.0.0.0 brd 0.0.0.0
4: docker0:  mtu 1500 qdisc noqueue 
 link/ether 02:42:ec:9d:25:76 brd ff:ff:ff:ff:ff:ff
 inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
 valid_lft forever preferred_lft forever
root@axcf2152:/opt/plcnext/# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:A0:45:9C:A1:13 
 inet addr:192.168.178.221 Bcast:192.168.178.255 Mask:255.255.255.0
 inet6 addr: fe80::2a0:45ff:fe9c:a113/64 Scope:Link
 UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
 RX packets:12358 errors:0 dropped:38 overruns:0 frame:0
 TX packets:2399 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000 
 RX bytes:1251098 (1.1 MiB) TX bytes:339883 (331.9 KiB)
 Interrupt:29 Base address:0xe000

You can see that the ifconfig command indicates that the interface is in promiscuous mode, and the ip a command - although not indicating this explicitly, like you would expect - does change its status from LOWER_UP to LOWER_UP100. I have been unable to find out what "LOWER_UP100" means, but it seems to have something to do with the change to promiscuous mode.

Hope this helps.

~ Martin.