search

benpan2002 / 0809ZJU007A

浙江大学 c mooc
MIT License
0 stars 0 forks source link

network issue: NO-CARRIER #4

Open benpannj opened 4 years ago

benpannj commented 4 years ago 
ip addr
<NO-CARRIER,BROADCAST,MULTICAST,UP>

From https://unix.stackexchange.com/questions/178921/what-does-no-carrier-and-down-mean-for-a-wireless-interface There is no document that would tell you what specially means for wireless. If your wifi is UP and NO-CARRIER means that is administratively up(ip link set dev wlan0 up) but not associated and authenticated with a SSID. Only LOWER_UP means that link layer is operational.

ip link list wlan0 and iw wlan0 link are 2 ways to retrieve link status information. The second form will show you if associated with a SSID, and show relevant wireless information.

Probably the cause of your link problems are related with Wireless power saving configurations, and thus the DORMANT state of your interface.

Netlink interface flags:

IFF_DORMANT - Driver signals dormant

Check out the links below with instructions on how to chance this behavior.

Additional Documentation:

benpannj commented 4 years ago

How to connect to a WPA/WPA2 WiFi network using Linux command line

This is a step-to-step guide for connecting to a WPA/WPA2 WiFi network via the Linux command line interface. The tools are:

wpa_supplicant
iw
ip
ping

iw is the basic tool for WiFi network-related tasks, such as finding the WiFi device name, and scanning access points. wpa_supplicant is the wireless tool for connecting to a WPA/WPA2 network. ip is used for enabling/disabling devices, and finding out general network interface information.

The steps for connecting to a WPA/WPA2 network are:

1. Find out the wireless device name.

$ /sbin/iw dev
phy#0
    Interface wlan0
        ifindex 3
        type managed

The above output showed that the system has 1 physical WiFi card, designated as phy#0. The device name is wlan0. The type specifies the operation mode of the wireless device. managed means the device is a WiFi station or client that connects to an access point.

2. Check that the wireless device is up.

$ ip link show wlan0
3: wlan0: (BROADCAST,MULTICAST) mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 1000
    link/ether 74:e5:43:a1:ce:65 brd ff:ff:ff:ff:ff:ff

Look for the word "UP" inside the brackets in the first line of the output.

In the above example, wlan0 is not UP. Execute the following command to bring it up:

$ sudo ip link set wlan0 up  
[sudo] password for peter:

Note: you need root privilege for the above operation.

If you run the show link command again, you can tell that wlan0 is now UP.

$ ip link show wlan0
3: wlan0: (NO-CARRIER,BROADCAST,MULTICAST,UP) mtu 1500 qdisc mq state DOWN mode DEFAULT qlen 1000
    link/ether 74:e5:43:a1:ce:65 brd ff:ff:ff:ff:ff:ff

3. Check the connection status.

$ /sbin/iw wlan0 link
Not connected.

The above output shows that you are not connected to any network.

4. Scan to find out what WiFi network(s) are detected

$ sudo /sbin/iw wlan0 scan
BSS 00:14:d1:9c:1f:c8 (on wlan0)
        ... sniped ...
    freq: 2412
    SSID: gorilla
    RSN:     * Version: 1
         * Group cipher: CCMP
         * Pairwise ciphers: CCMP
         * Authentication suites: PSK
         * Capabilities: (0x0000)
        ... sniped ...

The 2 important pieces of information from the above are the SSID and the security protocol (WPA/WPA2 vs WEP). The SSID from the above example is gorilla. The security protocol is RSN, also commonly referred to as WPA2. The security protocol is important because it determines what tool you use to connect to the network.

5. Connect to WPA/WPA2 WiFi network.

This is a 2 step process. First, you generate a configuration file for wpa_supplicant that contains the pre-shared key ("passphrase") for the WiFi network.

$ sudo -s
[sudo] password for peter: 
$ wpa_passphrase gorilla >> /etc/wpa_supplicant.conf 
...type in the passphrase and hit enter...

wpa_passphrase takes the SSID as the single argument. You must type in the passphrase for the WiFi network gorilla after you run the command. Using that information, wpa_passphrase will output the necessary configuration statements to the standard output. Those statements are appended to the wpa_supplicant configuration file located at /etc/wpa_supplicant.conf.

Note: you need root privilege to write to /etc/wpa_supplicant.conf.

$ cat /etc/wpa_supplicant.conf 
# reading passphrase from stdin
network={
    ssid="gorilla"
    #psk="testtest"
    psk=4dfe1c985520d26a13e932bf0acb1d4580461dd854ed79ad1a88ec221a802061
}

The second step is to run wpa_supplicant with the new configuration file.

$ sudo wpa_supplicant -B -D wext -i wlan0 -c /etc/wpa_supplicant.conf

-B means run wpa_supplicant in the background.
-D specifies the wireless driver. wext is the generic driver.
-c specifies the path for the configuration file.

Use the iw command to verify that you are indeed connected to the SSID.

$ /sbin/iw wlan0 link
Connected to 00:14:d1:9c:1f:c8 (on wlan0)
    SSID: gorilla
    freq: 2412
    RX: 63825 bytes (471 packets)
    TX: 1344 bytes (12 packets)
    signal: -27 dBm
    tx bitrate: 6.5 MBit/s MCS 0

    bss flags:  short-slot-time
    dtim period:    0
    beacon int: 100

6. Obtain IP address by DHCP

$ sudo dhclient wlan0

Use the ip command to verify the IP address assigned by DHCP. The IP address is 192.168.1.113 from below.

$ ip addr show wlan0
3: wlan0:  mtu 1500 qdisc mq state UP qlen 1000
    link/ether 74:e5:43:a1:ce:65 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.113/24 brd 192.168.1.255 scope global wlan0
    inet6 fe80::76e5:43ff:fea1:ce65/64 scope link 
       valid_lft forever preferred_lft forever

7. Add default routing rule.

The last configuration step is to make sure that you have the proper routing rules.

$ ip route show
192.168.1.0/24 dev wlan0  proto kernel  scope link  src 192.168.1.113

The above routing table contains only 1 rule which redirects all traffic destined for the local subnet (192.168.1.x) to the wlan0 interface. You may want to add a default routing rule to pass all other traffic through wlan0 as well.

$ sudo ip route add default via 192.168.1.254 dev wlan0
$ ip route show
default via 192.168.1.254 dev wlan0 
192.168.1.0/24 dev wlan0  proto kernel  scope link  src 192.168.1.113

8. ping external ip address to test connectivity

$ ping 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_req=1 ttl=48 time=135 ms
64 bytes from 8.8.8.8: icmp_req=2 ttl=48 time=135 ms
64 bytes from 8.8.8.8: icmp_req=3 ttl=48 time=134 ms
^C
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 134.575/134.972/135.241/0.414 ms

The above series of steps is a very verbose explanation of how to connect a WPA/WPA2 WiFi network. Some steps can be skipped as you connect to the same access point for a second time. For instance, you already know the WiFi device name, and the configuration file is already set up for the network. The process needs to be tailored according to your situation.

benpannj commented 4 years ago

cat /etc/dhcpcd.conf

# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.

# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel

# Inform the DHCP server of our hostname for DDNS.
#hostname

# Use the hardware address of the interface for the Client ID.
#clientid
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# Some non-RFC compliant DHCP servers do not reply with this set.
# In this case, comment out duid and enable clientid above.
duid

# Persist interface configuration when dhcpcd exits.
persistent

# vendorclassid is set to blank to avoid sending the default of
# dhcpcd-<version>:<os>:<machine>:<platform>
vendorclassid

# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search
option classless_static_routes
# Respect the network MTU. This is applied to DHCP routes.
option interface_mtu

# Request a hostname from the network
option host_name

# Most distributions have NTP support.
#option ntp_servers

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# Generate SLAAC address using the Hardware Address of the interface
#slaac hwaddr
# OR generate Stable Private IPv6 Addresses based from the DUID
slaac private
noipv4ll