我在 Raspberry Pi Compute Module 3（和 IO 板）上运行 Ubuntu Core，并通过 USB 连接了 Quectel EC21 LTE 调制解调器。我很难让它工作。
下列的Ubuntu Core 文档网站上的指南，我可以看到调制解调器出现：
$ sudo modem-manager.mmcli -L
Found 1 modems:
/org/freedesktop/ModemManager1/Modem/1 [Quectel] EC21
我可以看到一些关于它的好信息：
$ sudo modem-manager.mmcli -m 1
/org/freedesktop/ModemManager1/Modem/1 (device id 'a7dea8991786834fd4f5937baf2bae98f64e16dd')
-------------------------
Hardware | manufacturer: 'Quectel'
| model: 'EC21'
| revision: 'EC21AUTFAR02A03M4G'
| supported: 'gsm-umts, lte'
| current: 'gsm-umts, lte'
| equipment id: '861108030174782'
-------------------------
System | device: '/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.2'
| drivers: 'option1'
| plugin: 'Generic'
| primary port: 'ttyUSB2'
| ports: 'ttyUSB0 (qcdm), ttyUSB2 (at), ttyUSB3 (at)'
-------------------------
Numbers | own : 'unknown'
-------------------------
Status | lock: 'none'
| unlock retries: 'unknown'
| state: 'connected'
| power state: 'on'
| access tech: 'lte'
| signal quality: '80' (recent)
-------------------------
Modes | supported: 'allowed: 2g, 3g, 4g; preferred: none'
| current: 'allowed: 2g, 3g, 4g; preferred: none'
-------------------------
Bands | supported: 'unknown'
| current: 'unknown'
-------------------------
IP | supported: 'ipv4, ipv6, ipv4v6'
-------------------------
3GPP | imei: '861108030174782'
| enabled locks: 'none'
| operator id: '50501'
| operator name: 'Telstra Mobile Telstra'
| subscription: 'unknown'
| registration: 'home'
-------------------------
SIM | path: '/org/freedesktop/ModemManager1/SIM/1'
-------------------------
Bearers | paths: '/org/freedesktop/ModemManager1/Bearer/0'
如果我遵循本指南的其余部分，即：
$ sudo nmcli c add type gsm ifname ttyUSB2 con-name 4G apn telstra.internet
Connection '4G' (7640a17c-c7f4-40c7-9490-bfb0d22e28f1) successfully added.
$ sudo nmcli r wwan on
我似乎获得了一个 IP 地址：
$ ip addr
4: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 3
link/ppp
inet 10.98.27.23/32 brd 10.98.27.23 scope global ppp0
valid_lft forever preferred_lft forever
这是日志的输出：
$ sudo journalctl --no-pager -u snap.network-manager.networkmanager.service
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.0949] settings: Failed to add 7640a17c-c7f4-40c7-9490-bfb0d22e28f1/'4G': Plugin does not support adding connections
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.0984] keyfile: loading from file "/var/snap/network-manager/265/conf/system-connections/4G"...
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.0987] settings-connection[0x12b6590]: constructed (NMKeyfileConnection)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1014] settings-connection[0x12b6590,7640a17c-c7f4-40c7-9490-bfb0d22e28f1]: replace settings from connection 0x754040c0 (4G)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <info> [1523928492.1049] keyfile: add connection /var/snap/network-manager/265/conf/system-connections/4G (7640a17c-c7f4-40c7-9490-bfb0d22e28f1,"4G")
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1055] settings-connection[0x12b6590,7640a17c-c7f4-40c7-9490-bfb0d22e28f1]: failed to read connection timestamp: Key file does not have key '7640a17c-c7f4-40c7-9490-bfb0d22e28f1' in group 'timestamps'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1088] ++ connection 'new connection' (0x12b6590/NMKeyfileConnection): [/org/freedesktop/NetworkManager/Settings/2]
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1090] ++ connection [ 0x12fd2a8 ]
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1091] ++ connection.id = '4G'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1092] ++ connection.interface-name = 'ttyUSB2'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1093] ++ connection.permissions = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1094] ++ connection.secondaries = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1095] ++ connection.type = 'gsm'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1096] ++ connection.uuid = '7640a17c-c7f4-40c7-9490-bfb0d22e28f1'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1097] ++ gsm [ 0x1332b30 ]
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1098] ++ gsm.apn = 'telstra.internet'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1099] ++ gsm.number = '*99#'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1100] ++ ipv4 [ 0x1310bc8 ]
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1101] ++ ipv4.addresses = ((GPtrArray*) 0x1303660)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1102] ++ ipv4.dns = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1103] ++ ipv4.dns-search = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1104] ++ ipv4.method = 'auto'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1105] ++ ipv4.routes = ((GPtrArray*) 0x12f7fc8)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1106] ++ ipv6 [ 0x1310c90 ]
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1107] ++ ipv6.addresses = ((GPtrArray*) 0x12f8180)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1108] ++ ipv6.dns = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1109] ++ ipv6.dns-search = []
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1110] ++ ipv6.method = 'auto'
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1111] ++ ipv6.routes = ((GPtrArray*) 0x12f7478)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1127] create NMAuditManager singleton (0x75300d50)
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <info> [1523928492.1129] audit: op="connection-add" uuid="7640a17c-c7f4-40c7-9490-bfb0d22e28f1" name="4G" pid=3186 uid=0 result="success"
Apr 17 01:28:12 localhost.localdomain NetworkManager[1489]: <debug> [1523928492.1168] Saving secrets for connection /org/freedesktop/NetworkManager/Settings/2 (4G)
Apr 17 01:28:28 localhost.localdomain NetworkManager[1489]: <debug> [1523928508.6772] manager: (WWAN): setting radio enabled by user
Apr 17 01:28:28 localhost.localdomain NetworkManager[1489]: <info> [1523928508.6842] audit: op="radio-control" arg="wwan-enabled:1" pid=3201 uid=0 result="success"
但是，如果我使用界面执行诸如 ping 之类的操作ppp，则什么也得不到：
$ sudo ping -I ppp0 8.8.8.8
我需要做什么才能使 WWAN 接口正常工作？
答案1
实际上，最后相当简单 - 我所要做的就是通过以太网删除默认网关。我不确定为什么我的绑定地址ping不起作用，但无论如何，在我运行后它起作用了：
$ sudo ip route delete default via 192.168.30.254
（该 IP 是我所在 LAN 的默认网关）
现在 Quectel EC21 会自动连接！鉴于 Quectel 缺乏有用的文档，这让我非常惊讶 - 但事实就是如此。