OpenWRT Chaos Calmer 15.05 on Dlink DIR-320 with CDMA modem
Thursday, April 7th, 2016 01:53 pm GMT +2

The goal of this article is to install latest OpenWRT firmware on a very popular DIR-320 Wi-Fi router (BRCM47XX based). The reason why you might do this is to be able to connect modern hardware(modems) to this pretty old legacy device.

Official firmware 3G modem support list is pretty limited and uses old kernel. On the other hand, there is an alternative DD-WRT firwmare with linux kernel 2.6.x which is pretty old also. Therefore, the only viable option is installing OpenWRT which ships the latest linux kernels 3.18.xx.

As a bonus sub-topic we’ll consider setting up an external CDMA(EVDO) modem and using it to access internet.



In order to proceed and experiment by yourself the following is necessary:

  • Dlink DIR-320 router (rev. A1/A2 only!, be careful as there are B1/B2/NRU versions which are completely different hardware!)
  • RJ45 CAT5 Patch cable
  • USB to Serial adapter (I’ve been able to successfully use cheap PL2303TA based USB TTL to RS232)
  • USB flash card or hard drive
  • USB 3G modem (in my case it’s Sierra AirCard 250U)
  • USB Hub (external power source is highly recommended)
  • x86_64 Linux host system (i’m using Ubuntu 15.10 x86_64)
  • a lot of patience :)

Install OpenWRT using Image builder for brcm47xx/legacy

On your host linux system, download and unpack OpenWRT image builder packages:

bananos@ubby:$ wget "https://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/OpenWrt-ImageBuilder-15.05.1-brcm47xx-legacy.Linux-x86_64.tar.bz2"
bananos@ubby:$ tar -xvvf "OpenWrt-ImageBuilder-15.05.1-brcm47xx-legacy.Linux-x86_64.tar.bz2"

After that, we’re going to assemble our custom firmware out of pre-built packages. Image builder was created specifically to overcome the slowness and complexity of compiling OpenWRT from sources.

bananos@ubby:$ sudo apt-get install -y subversion build-essential libncurses5-dev zlib1g-dev gawk git ccache gettext libssl-dev xsltproc
bananos@ubby:$ cd "OpenWrt-ImageBuilder-15.05.1-brcm47xx-legacy.Linux-x86_64"
bananos@ubby:$ make image PROFILE="Broadcom-b43" PACKAGES="base-files libc libgcc busybox kmod-usb2 kmod-usb-ohci kmod-usb-uhci kmod-usb-storage kmod-fs-ext4 block-mount kmod-scsi-core -dropbear mtd uci -opkg netifd fstools swconfig wpad-mini nvram -otrx kmod-leds-gpio kmod-gpio-button-hotplug kmod-ledtrig-default-on kmod-ledtrig-timer kmod-ledtrig-netdev dnsmasq iptables -ip6tables ppp ppp-mod-pppoe kmod-nf-nathelper firewall odhcpd odhcp6c"

make[1]: Entering directory '/home/bananos/Projects/openwrt_dir320/image_builder/OpenWrt-ImageBuilder-15.05.1-brcm47xx-legacy.Linux-x86_64'
echo 'Building images for brcm47xx - Broadcom SoC, all Ethernet, BCM43xx WiFi (b43, default)'
Building images for brcm47xx - Broadcom SoC, all Ethernet, BCM43xx WiFi (b43, default)
echo 'Packages: base-files block-mount busybox dnsmasq firewall fstools iptables kernel kmod-b43 kmod-b43legacy kmod-fs-ext4 kmod-gpio-button-hotplug kmod-leds-gpio kmod-ledtrig-default-on kmod-ledtrig-netdev kmod-ledtrig-timer kmod-nf-nathelper kmod-scsi-core kmod-usb-ohci kmod-usb-storage kmod-usb-uhci kmod-usb2 libc libgcc mtd netifd nvram odhcp6c odhcpd ppp ppp-mod-pppoe swconfig uci wpad-mini'
Packages: base-files block-mount busybox dnsmasq firewall fstools iptables kernel kmod-b43 kmod-b43legacy kmod-fs-ext4 kmod-gpio-button-hotplug kmod-leds-gpio kmod-ledtrig-default-on kmod-ledtrig-netdev kmod-ledtrig-timer kmod-nf-nathelper kmod-scsi-core kmod-usb-ohci kmod-usb-storage kmod-usb-uhci kmod-usb2 libc libgcc mtd netifd nvram odhcp6c odhcpd ppp ppp-mod-pppoe swconfig uci wpad-mini
echo

rm -rf /home/bananos/Projects/openwrt_dir320/image_builder/OpenWrt-ImageBuilder-15.05.1-brcm47xx-legacy.Linux-x86_64/build_dir/target-mipsel_mips32_uClibc-0.9.33.2/root-brcm47xx
.....

Note the - symbol before some of the packages, this means that those must be excluded from resulting build. As a result our target image will have almost nothing except external usb support and bare linux kernel. This is due to really tiny capacity of the internal router storage(4Mb). In order to increase it we’ll be using external USB storage(extroot) which is covered in detail in the next sections of this article.

Make sure you have active connection to internet as Image Builder will download some packages from the online repository. At the end of the build, you should be able to find a bunch of prepackaged firmwares in bin/ directory:

bananos@ubby:$ ls bin/brcm47xx/ | grep "asus"

openwrt-15.05.1-brcm47xx-legacy-asus-wl-300g-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-320gp-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-330ge-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-500gp-v1-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-500gp-v2-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-500w-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-520gu-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-550ge-squashfs.trx
openwrt-15.05.1-brcm47xx-legacy-asus-wl-hdd25-squashfs.trx

Our file of interest is openwrt-15.05.1-brcm47xx-legacy-asus-wl-500gp-v2-squashfs.trx since Asus WL500gp-V2 uses the same hardware as Dlink DIR-320 Rev A.

Firmware Flashing

There are a lot of firmware flashing instructions on the net, but we’ll be using the most generic and reliable via TFTP. Create the following bash file named flash.sh:

#!/bin/bash
echo "=================================================================="
echo "This script will upload dd-wrt firmware (firmware.bin)"
echo "in the current directory to 192.168.0.1 "
echo "during the router's bootup. "
echo ""
echo "* Set your ethernet card's settings to: "
echo "     IP:      192.168.0.10 "
echo "     Mask:    255.255.255.0 "
echo "     Gateway: 192.168.0.1 "
echo "* Unplug the router's power cable. "
echo ""
echo "Press Ctrl+C to abort or any other key to continue... "

read

echo ""
echo "* Re-plug the router's power cable. "
echo ""
echo "=================================================================="
echo "Waiting for the router... Press Ctrl+C to abort. "
echo ""

try(){
ping -c 1 -w 1 192.168.0.1
}
try

while [ "$?" != "0" ] ;
do
try
done
echo "*** Start Flashing **** "
atftp --no-source-port-checking -p -l firmware.bin 192.168.0.1
echo "Firmware successfully loaded!"

The script’s usage instructions are pretty self-explanatory, but before using it we must do a few more things:

bananos@ubby:$ chmod +x flash.sh
bananos@ubby:$ cp bin/brcm47xx/openwrt-15.05.1-brcm47xx-legacy-asus-wl-500gp-v2-squashfs.trx firmware.bin
bananos@ubby:$ sudo apt-get install -y atftp atftpd

Assuming that your USB-to-Serial adapter was detected as /dev/ttyUSB0, let’s open serial terminal to be able to observe what is happening on the router in real time:

bananos@ubby:$ sudo bash -c "screen /dev/ttyUSB0 115200"

Now, prepare your ethernet network card settings and

  • plug port #1 of your router to linux machine
  • run ./flash.sh and press any key to see a lot of connect: Network is unreachable messages
  • plug router power cable and wait for the flashing process to finish

In the serial console you’ll notice something similar to this:

Decompressing...........done

CFE version 1.0.37 for BCM947XX (32bit,SP,LE)
Build Date: Thu Jul 19 10:53:24 CST 2007 (root@redhat9)
Copyright (C) 2000,2001,2002,2003 Broadcom Corporation.

Initializing Arena
Initializing Devices.
Boot partition size = 262144(0x40000)
et0: Broadcom BCM47xx 10/100 Mbps Ethernet Controller 4.150.3.0
CPU type 0x29029: 240MHz
Total memory: 32768 KBytes

Total memory used by CFE:  0x80300000 - 0x803C0720 (788256)
Initialized Data:          0x80337730 - 0x8033AE50 (14112)
BSS Area:                  0x8033AE50 - 0x8033C720 (6352)
Local Heap:                0x8033C720 - 0x803A0720 (409600)
Stack Area:                0x803A0720 - 0x803C0720 (131072)
Text (code) segment:       0x80300000 - 0x80337730 (227120)
Boot area (physical):      0x003C1000 - 0x00401000
Relocation Factor:         I:00000000 - D:00000000

alpha bootcode ver 0.1.2
cmd = ifconfig eth0 -addr=192.168.0.1 -mask=255.255.255.0
We disable the arp for self.
We disable the arp for self.
Device eth0:  hwaddr 00-90-4C-C0-00-01, ipaddr 192.168.0.1, mask 255.255.255.0
        gateway not set, nameserver not set
cmd = go;
cmd = load -raw -addr=0x803c0720 -max=0x3a0000 :
Loader:raw Filesys:tftp Dev:eth0 File:: Options:(null)
Loading: entry point=803C0720
........... 3674112 bytes read
Entry at 0x803c0720
cmd = flash -noheader -mem -size=0x381000 0x803c0720 flash1.trx
Reading from 0x803c0720: Programming...done. 3674112 bytes written
Dest=80001000, source =803c0720, filename=flash1.trx
cmd = boot -raw -z -addr=0x80001000 -max=0x3a0000 flash0.os:
Loader:raw Filesys:raw Dev:flash0.os File: Options:(null)
Loading: entry point=80001000
.. 3712 bytes read
Entry at 0x80001000
Closing network.
Starting program at 0x80001000
[    0.000000] Linux version 3.18.23 (buildbot@builder1) (gcc version 4.8.3 (OpenWrt/Linaro GCC 4.8-2014.04 r48532) ) #1 Tue Mar 1 09:18:44 CET 2016
[    0.000000] CPU0 revision is: 00029029 (Broadcom BMIPS3300)
[    0.000000] bcm47xx: Using ssb bus
[    0.000000] ssb: Found chip with id 0x5354, rev 0x03 and package 0x00
[    0.000000] can not parse nvram name (null)boardnum(null) with value  got -22
[    0.000000] can not parse nvram name (null)rxpo2g(null) with value 0xfff8 got -34
[    0.000000] ssb: Sonics Silicon Backplane found at address 0x18000000
[    0.000000] Determined physical RAM map:
[    0.000000]  memory: 02000000 @ 00000000 (usable)
[    0.000000] Initrd not found or empty - disabling initrd
[    0.000000] Zone ranges:
[    0.000000]   Normal   [mem 0x00000000-0x01ffffff]
[    0.000000] Movable zone start for each node
[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x00000000-0x01ffffff]
[    0.000000] Initmem setup node 0 [mem 0x00000000-0x01ffffff]
[    0.000000] Primary instruction cache 16kB, VIPT, 4-way, linesize 16 bytes.
[    0.000000] Primary data cache 16kB, 2-way, VIPT, cache aliases, linesize 16 bytes
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 8128
[    0.000000] Kernel command line:  noinitrd console=ttyS0,115200
[    0.000000] PID hash table entries: 128 (order: -3, 512 bytes)
[    0.000000] Dentry cache hash table entries: 4096 (order: 2, 16384 bytes)
[    0.000000] Inode-cache hash table entries: 2048 (order: 1, 8192 bytes)
[    0.000000] Memory: 28956K/32768K available (2605K kernel code, 103K rwdata, 316K rodata, 164K init, 267K bss, 3812K reserved)
[    0.000000] NR_IRQS:128
[    0.000000] MIPS: machine is Unknown Board
[    0.060000] Calibrating delay loop... 239.61 BogoMIPS (lpj=1198080)
[    0.070000] pid_max: default: 32768 minimum: 301
[    0.070000] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.070000] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.080000] NET: Registered protocol family 16
[    0.100000] Switched to clocksource MIPS
[    0.110000] NET: Registered protocol family 2
[    0.110000] TCP established hash table entries: 1024 (order: 0, 4096 bytes)
[    0.110000] TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
[    0.110000] TCP: Hash tables configured (established 1024 bind 1024)
[    0.110000] TCP: reno registered
[    0.110000] UDP hash table entries: 256 (order: 0, 4096 bytes)
[    0.110000] UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
[    0.110000] NET: Registered protocol family 1
[    0.110000] futex hash table entries: 256 (order: -1, 3072 bytes)
[    0.120000] squashfs: version 4.0 (2009/01/31) Phillip Lougher
[    0.120000] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
[    0.120000] msgmni has been set to 56
[    0.120000] io scheduler noop registered
[    0.120000] io scheduler deadline registered (default)
[    0.120000] Serial: 8250/16550 driver, 16 ports, IRQ sharing enabled
[    0.130000] console [ttyS0] disabled
[    0.150000] serial8250.0: ttyS0 at MMIO 0xb8000300 (irq = 3, base_baud = 1562500) is a U6_16550A
[    0.450000] console [ttyS0] enabled
[    0.470000] serial8250.0: ttyS1 at MMIO 0xb8000400 (irq = 3, base_baud = 1562500) is a U6_16550A
[    0.490000] physmap platform flash device: 02000001 at 1c000000
[    0.490000] physmap-flash.0: Found 1 x16 devices at 0x0 in 8-bit bank. Manufacturer ID 0x000001 Chip ID 0x0000f6
[    0.500000] Amd/Fujitsu Extended Query Table at 0x0040
[    0.510000]   Amd/Fujitsu Extended Query version 1.1.
[    0.510000] physmap-flash.0: Swapping erase regions for top-boot CFI table.
[    0.520000] number of CFI chips: 1
[    0.530000] 6 bcm47xxpart partitions found on MTD device physmap-flash.0
[    0.540000] Creating 6 MTD partitions on "physmap-flash.0":
[    0.540000] 0x000000000000-0x000000040000 : "boot"
[    0.550000] 0x000000040000-0x0000003f0000 : "firmware"
[    0.560000] 0x00000004001c-0x00000004090c : "loader"
[    0.570000] 0x00000004090c-0x000000146000 : "linux"
[    0.580000] 0x000000146000-0x0000003f0000 : "rootfs"
[    0.580000] mtd: device 4 (rootfs) set to be root filesystem
[    0.590000] 1 squashfs-split partitions found on MTD device rootfs
[    0.600000] 0x000000380000-0x0000003f0000 : "rootfs_data"
[    0.600000] 0x0000003f0000-0x000000400000 : "nvram"
[    0.710000] libphy: Fixed MDIO Bus: probed
[    0.710000] b44: Broadcom 44xx/47xx 10/100 PCI ethernet driver version 2.0
[    0.730000] libphy: b44_eth_mii: probed
[    0.850000] b53_common: found switch: BCM5325, rev 0
[    0.860000] b44 ssb0:0: attached PHY driver [Broadcom B53 (1)] (mii_bus:phy_addr=1:1e)
[    0.870000] b44 ssb0:0 eth0: Broadcom 44xx/47xx 10/100 PCI ethernet driver 00:90:4c:c0:00:01
[    0.880000] bcm47xx-wdt bcm47xx-wdt.0: BCM47xx Watchdog Timer enabled (30 seconds, Software Timer)
[    0.890000] GPIO_WDT: failed to register misc device
[    0.890000] TCP: cubic registered
[    0.890000] NET: Registered protocol family 17
[    0.900000] bridge: automatic filtering via arp/ip/ip6tables has been deprecated. Update your scripts to load br_netfilter if you need this.
[    0.910000] Bridge firewalling registered
[    0.920000] 8021q: 802.1Q VLAN Support v1.8
[    0.940000] VFS: Mounted root (squashfs filesystem) readonly on device 31:4.
[    0.950000] Freeing unused kernel memory: 164K (802f7000 - 80320000)
[    2.620000] init: Console is alive
[    2.630000] init: - watchdog -
[    5.430000] usbcore: registered new interface driver usbfs
[    5.430000] usbcore: registered new interface driver hub
[    5.440000] usbcore: registered new device driver usb
[    5.640000] SCSI subsystem initialized
[    5.670000] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[    5.680000] ehci-platform: EHCI generic platform driver
[    5.680000] ehci-platform ehci-platform.0: EHCI Host Controller
[    5.690000] ehci-platform ehci-platform.0: new USB bus registered, assigned bus number 1
[    5.700000] ehci-platform ehci-platform.0: irq 6, io mem 0x18003800
[    5.730000] ehci-platform ehci-platform.0: USB 2.0 started, EHCI 1.00
[    5.730000] hub 1-0:1.0: USB hub found
[    5.740000] hub 1-0:1.0: 2 ports detected
[    5.750000] ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
[    5.760000] ohci-platform: OHCI generic platform driver
[    5.770000] ohci-platform ohci-platform.0: Generic Platform OHCI controller
[    5.780000] ohci-platform ohci-platform.0: new USB bus registered, assigned bus number 2
[    5.790000] ohci-platform ohci-platform.0: irq 6, io mem 0x18003000
[    5.850000] hub 2-0:1.0: USB hub found
[    5.860000] hub 2-0:1.0: 2 ports detected
[    5.870000] uhci_hcd: USB Universal Host Controller Interface driver
[    5.890000] usbcore: registered new interface driver usb-storage
[    6.680000] init: - preinit -
[    7.170000] b44 ssb0:0 eth0: Link is up at 100 Mbps, half duplex
[    7.180000] b44 ssb0:0 eth0: Flow control is off for TX and off for RX
[    7.460000] random: mktemp urandom read with 11 bits of entropy available
Press the [f] key and hit [enter] to enter failsafe mode
Press the [1], [2], [3] or [4] key and hit [enter] to select the debug level
[    8.980000] b44 ssb0:0 eth0: Link is Up - 100Mbps/Full - flow control off
[   11.010000] mount_root: loading kmods from internal overlay
[   11.380000] block: attempting to load /etc/config/fstab
[   11.390000] block: unable to load configuration (fstab: Entry not found)
[   11.400000] block: no usable configuration
[   11.400000] mount_root: jffs2 not ready yet, using temporary tmpfs overlay
[   11.460000] b44 ssb0:0 eth0: powering down PHY
[   11.490000] procd: - early -
[   11.500000] procd: - watchdog -
[   12.000000] b44 ssb0:0 eth0: Link is Down
[   12.410000] procd: - ubus -
[   13.430000] procd: - init -
Please press Enter to activate this console.
[   17.510000] NET: Registered protocol family 10
[   17.530000] Loading modules backported from Linux version master-2015-03-09-0-g141f155
[   17.540000] Backport generated by backports.git backports-20150129-0-gdd4a670
[   17.560000] nf_conntrack version 0.5.0 (455 buckets, 1820 max)
[   17.670000] xt_time: kernel timezone is -0000
[   17.730000] cfg80211: Calling CRDA to update world regulatory domain
[   17.740000] ip_tables: (C) 2000-2006 Netfilter Core Team
[   17.770000] cfg80211: World regulatory domain updated:
[   17.770000] cfg80211:  DFS Master region: unset
[   17.780000] cfg80211:   (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp), (dfs_cac_time)
[   17.790000] cfg80211:   (2402000 KHz - 2472000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)
[   17.800000] cfg80211:   (2457000 KHz - 2482000 KHz @ 20000 KHz, 92000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[   17.810000] cfg80211:   (2474000 KHz - 2494000 KHz @ 20000 KHz), (N/A, 2000 mBm), (N/A)
[   17.820000] cfg80211:   (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[   17.830000] cfg80211:   (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (0 s)
[   17.840000] cfg80211:   (5490000 KHz - 5730000 KHz @ 160000 KHz), (N/A, 2000 mBm), (0 s)
[   17.840000] cfg80211:   (5735000 KHz - 5835000 KHz @ 80000 KHz), (N/A, 2000 mBm), (N/A)
[   17.850000] cfg80211:   (57240000 KHz - 63720000 KHz @ 2160000 KHz), (N/A, 0 mBm), (N/A)
[   18.230000] PPP generic driver version 2.4.2
[   18.240000] NET: Registered protocol family 24
[   18.410000] b43-phy0: Broadcom 5354 WLAN found (core revision 13)
[   18.440000] b43-phy0: Found PHY: Analog 6, Type 5 (LP), Revision 0
[   18.450000] b43-phy0: Found Radio: Manuf 0x17F, ID 0x2062, Revision 1, Version 0
[   18.470000] Broadcom 43xx driver loaded [ Features: PNL ]
[   18.550000] Broadcom 43xx-legacy driver loaded [ Features: PLD ]
[   26.610000] b44 ssb0:0 eth0: Link is up at 100 Mbps, full duplex
[   26.610000] b44 ssb0:0 eth0: Flow control is off for TX and off for RX
[   28.030000] b44 ssb0:0 eth0: Link is Up - 100Mbps/Full - flow control off
[   31.430000] jffs2_scan_eraseblock(): End of filesystem marker found at 0x0
[   31.450000] jffs2_build_filesystem(): unlocking the mtd device... done.
[   31.450000] jffs2_build_filesystem(): erasing all blocks after the end marker... ^[[A^[[A
[   34.450000] b44 ssb0:0 eth0: powering down PHY
[   34.530000] b44 ssb0:0 eth0: Link is up at 100 Mbps, full duplex
[   34.540000] b44 ssb0:0 eth0: Flow control is off for TX and off for RX
[   34.580000] device eth0.1 entered promiscuous mode
[   34.580000] device eth0 entered promiscuous mode
[   34.600000] br-lan: port 1(eth0.1) entered forwarding state
[   34.610000] br-lan: port 1(eth0.1) entered forwarding state
[   35.830000] done.
[   35.830000] jffs2: notice: (845) jffs2_build_xattr_subsystem: complete building xattr subsystem, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.
[   36.610000] br-lan: port 1(eth0.1) entered forwarding state
[   80.480000] random: nonblocking pool is initialized

BusyBox v1.23.2 (2016-03-01 08:53:11 CET) built-in shell (ash)

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 CHAOS CALMER (15.05.1, r48532)
 -----------------------------------------------------
  * 1 1/2 oz Gin            Shake with a glassful
  * 1/4 oz Triple Sec       of broken ice and pour
  * 3/4 oz Lime Juice       unstrained into a goblet.
  * 1 1/2 oz Orange Juice
  * 1 tsp. Grenadine Syrup
 -----------------------------------------------------
root@OpenWrt:/#

After successful flash procedure, reboot your router by powering it off and setting your ethernet network card back to DHCP (that’s necessary because the default router DHCP server assigns addresses in 192.168.1.XXX subnet, which is different from 192.168.0.XXX which we used for flashing purposes)

Turn on the device once again and wait until wired connection with your host system establishes. After that, you may happily telnet into the router:

bananos@ubby:$ telnet 192.168.1.1
Trying 192.168.1.1...
Connected to 192.168.1.1.
Escape character is '^]'.
 === IMPORTANT ============================
  Use 'passwd' to set your login password
  this will disable telnet and enable SSH
 ------------------------------------------

BusyBox v1.23.2 (2016-03-01 08:53:11 CET) built-in shell (ash)

.....

Congrats! The first, most important step is completed. In the next section we’ll configure extroot to be able to install additional OpenWrt packages such as LuCI and various kernel modules.

Setting up extroot

Connect your USB drive to linux host system. The first thing we’re going to do is partitioning. Assuming that your newly inserted disk is /dev/sdb I would suggest somewhat similar to this:

bananos@ubby:$ sudo fdisk -l /dev/sdb
Disk /dev/sdb: 28 GiB, 30005821440 bytes, 58605120 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xa58948b4

Device     Boot   Start      End  Sectors   Size Id Type
/dev/sdb1            63  2008124  2008062 980.5M 82 Linux swap / Solaris
/dev/sdb2       2008125  6024374  4016250   1.9G 83 Linux
/dev/sdb3       6024375 58605119 52580745  25.1G 83 Linux

In my case, I’m using 1.8 inch TOSHIBA MK3008GAL hard drive. To make partitioning table similar to above mentioned you may use GUI tool called GParted or use plain fdisk. Primary partition usage is as follows:

  • /dev/sdb1 is for swapping purposes due to a low (32Mb) amount of RAM
  • /dev/sdb2 is for root filesystem (rootfs /)
  • /dev/sdb3 is for home directory (/home)

After partitioning, format rootfs and /home into ext4 filesystems:

bananos@ubby:$ sudo umount /dev/sdb2
bananos@ubby:$ sudo mkfs.ext4 /dev/sdb2
mke2fs 1.42.12 (29-Aug-2014)
Creating filesystem with 502031 4k blocks and 125696 inodes
Filesystem UUID: 69b17872-9486-4113-8d9f-59a5e4221027
Superblock backups stored on blocks:
    32768, 98304, 163840, 229376, 294912

Allocating group tables: done
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

bananos@ubby:$ sudo umount /dev/sdb3
bananos@ubby:$ sudo mkfs.ext4 /dev/sdb3

....

bananos@ubby:$ sudo mkswap /dev/sdb1
Setting up swapspace version 1, size = 980.5 MiB (1028120576 bytes)
no label, UUID=457a57b6-aae0-410a-8832-4e182e15e04b

Now, connect USB drive to your router, turn it on, and telnet once again:

root@OpenWrt:/# logread | grep "sda"
Tue Mar  1 08:15:13 2016 kern.notice kernel: [    7.290000] sd 0:0:0:0: [sda] 58605120 512-byte logical blocks: (30.0 GB/27.9 GiB)
Tue Mar  1 08:15:13 2016 kern.notice kernel: [    7.320000] sd 0:0:0:0: [sda] Write Protect is off
Tue Mar  1 08:15:13 2016 kern.debug kernel: [    7.320000] sd 0:0:0:0: [sda] Mode Sense: 03 00 00 00
Tue Mar  1 08:15:13 2016 kern.err kernel: [    7.330000] sd 0:0:0:0: [sda] No Caching mode page found
Tue Mar  1 08:15:13 2016 kern.err kernel: [    7.330000] sd 0:0:0:0: [sda] Assuming drive cache: write through
Tue Mar  1 08:15:13 2016 kern.info kernel: [    7.400000]  sda: sda1 sda2 sda3
Tue Mar  1 08:15:13 2016 kern.notice kernel: [    7.440000] sd 0:0:0:0: [sda] Attached SCSI disk

We’ve just used logread to make sure that hard drive was successfully detected by kernel. Now, let’s proceed to creating external rootfs:

root@OpenWrt:/# ls -l /dev/sda
brw-r--r--    1 root     root        8,   0 Jan  1  1970 /dev/sda
root@OpenWrt:/# block detect
config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '1'
        option  auto_mount      '1'
        option  delay_root      '5'
        option  check_fs        '0'

config 'swap'
        option  uuid    '457a57b6-aae0-410a-8832-4e182e15e04b'
        option  enabled '0'

config 'mount'
        option  target  '/mnt/sda2'
        option  uuid    '69b17872-9486-4113-8d9f-59a5e4221027'
        option  enabled '0'

config 'mount'
        option  target  '/mnt/sda3'
        option  uuid    '37582519-c560-45d3-9a4e-9a95d255b33a'
        option  enabled '0'

We’ve just seen that usb hard drive is present at /dev/sda and has 3 partitions. Next, we’ll create a so-called pivot-overlay:

root@OpenWrt:/# mount /dev/sda2 /mnt ; tar -C /overlay -cvf - . | tar -C /mnt -xf - ; umount /mnt
./
./.fs_state
./work/
./work/work/
./upper/
./upper/etc/
./upper/etc/uci-defaults/
./upper/etc/uci-defaults/11_migrate-sysctl
./upper/etc/uci-defaults/03_network_migration
./upper/etc/uci-defaults/odhcpd.defaults
./upper/etc/uci-defaults/10_migrate-shadow
./upper/etc/uci-defaults/10-fstab
./upper/etc/uci-defaults/12_network-generate-ula
./upper/etc/uci-defaults/09_fix_crc
./upper/etc/config/
./upper/etc/config/dhcp
./upper/etc/config/fstab
./upper/etc/config/firewall
./upper/etc/config/network
./upper/etc/config/system
./upper/etc/config/wireless
./upper/etc/ethers
./upper/etc/dnsmasq.time

The above mentioned command will mount /dev/sda2 as /mnt, then will copy everything from /overlay to /mnt and unmount partition. Now, create fstab template:

root@OpenWrt:/# block detect > /etc/config/fstab ; vi /etc/config/fstab

After editing your fstab file it should look like following:

config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '1'
        option  auto_mount      '1'
        option  delay_root      '5'
        option  check_fs        '1'

config 'swap'
        option  enabled '1'
        option  device '/dev/sda1'

config 'mount'
        option  target  '/overlay'
        option  enabled '1'
        option  device  '/dev/sda2'
        option  fstype  'ext4'
        option  options 'rw,relatime,data=ordered,async,errors=remount-ro'
        option  enabled_fsck '1'

config 'mount'
        option  target  '/home'
        option  enabled '1'
        option  device '/dev/sda3'
        option  fstype  'ext4'
        option  options 'rw,relatime,data=ordered,async,errors=remount-ro'
        option  enabled_fsck '1'

Don’t forget to create /home directory by entering mkdir -p /home! Now, reboot your router and check that everything was mounted correctly:

root@OpenWrt:/# df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                    1.9G      2.9M      1.7G   0% /
/dev/root                 2.3M      2.3M         0 100% /rom
tmpfs                    14.2M     44.0K     14.2M   0% /tmp
/dev/sda2                 1.9G      2.9M      1.7G   0% /overlay
overlayfs:/overlay        1.9G      2.9M      1.7G   0% /
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sda3                24.6G     43.9M     23.2G   0% /home

root@OpenWrt:/# swapon -s
Filename                                Type            Size    Used    Priority
/dev/sda1                               partition       1004024 0       -1

We can see here, that rootfs(/) partition now has 1.7G of free space, and there’s almost 998M of swap. That’s it! External root filesystem is ready to use. In the next step, we’ll install opkg package manager, to be able to do something useful with our fresh linux system.

Installation of package manager (opkg)

A bare linux system is of no use if we’re not able to install additional software. That’s what we’ll accomplish in this section. Since we don’t have access to internet(yet) from the router itself, we’ll download opkg binary package manually and install it on the working system.

As an additional option you may consider downloading all of the OpenWRT binary packages to newly prepared usb drive if you have plenty of free space. That’s very useful if there will be no access to internet from the router itself during spontaneous connection failures or maintenance periods.

Re-attach hard drive to linux host system and assuming that
/media/bananos/69b17872-9486-4113-8d9f-59a5e4221027 is your /home directory mentioned above, download all packages:

root@ubby:$ cd `/media/bananos/69b17872-9486-4113-8d9f-59a5e4221027` && mkdir repo && cd repo
root@ubby:$ wget -r --no-parent --reject "index.html*" "https://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/"
......

FINISHED --2016-03-31 16:48:54--
Total wall clock time: 7m 23s
Downloaded: 4508 files, 307M in 2m 9s (2.39 MB/s)

This will download all packages from https://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/ preserving directory structure. Let’s make it more clean:

root@ubby:$ mv downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/* .
root@ubby:$ rm -rf downloads.openwrt.org/
root@ubby:# ls
base luci  management  packages  routing  telephony

Now, let’s install opkg manager by copying corresponding package to rootfs:

root@ubby:$ cp base/opkg_9c97d5ecd795709c8584e972bfdf3aee3a5b846d-9_brcm47xx.ipk /media/bananos/37582519-c560-45d3-9a4e-9a95d255b33a/opkg.ipk
root@ubby:$ cd /media/bananos/37582519-c560-45d3-9a4e-9a95d255b33a/

root@ubby:$ 7z x opkg.ipk

7-Zip [64] 9.20  Copyright (c) 1999-2010 Igor Pavlov  2010-11-18
p7zip Version 9.20 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,2 CPUs)

Processing archive: opkg.ipk
Extracting  opkg
Everything is Ok
Size:       71680
Compressed: 64546

root@ubby:$ tar -xvf opkg
./debian-binary
./data.tar.gz
./control.tar.gz

root@ubby:$ rm control.tar.gz opkg.ipg debian-binary rm opkg

Unplug USB-hdd from host system and replug it back to router, run telnet and check that data.tar.gz is at /overlay:

root@OpenWrt:/# ls /overlay/
data.tar.gz  etc          lost+found   upper        work
root@OpenWrt:/# mv /overlay/data.tar.gz /
root@OpenWrt:/# tar -xzvf data.tar.gz
./
./lib/
./lib/upgrade/
./lib/upgrade/keep.d/
./lib/upgrade/keep.d/opkg
./bin/
./bin/opkg
./usr/
./usr/lib/
./usr/lib/opkg/
./usr/sbin/
./usr/sbin/opkg-key
./etc/
./etc/uci-defaults/
./etc/uci-defaults/20_migrate-feeds
./etc/opkg/
./etc/opkg/customfeeds.conf
./etc/opkg/distfeeds.conf
./etc/opkg.conf

If everything was correct and you extracted tar package directly to / then it is possible to run opkg itself:

root@OpenWrt:/# opkg --version
opkg version 0.1.8

Now, if you have working internet connection it is possible to install additional OpenWRT packages like LuCI, but we’re going to leverage our offline repo we’ve created above. Open /etc/opkg/distfeeds.conf and create following file contents:

#src/gz chaos_calmer_base http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/base
#src/gz chaos_calmer_luci http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/luci
#src/gz chaos_calmer_packages http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/packages
#src/gz chaos_calmer_routing http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/routing
#src/gz chaos_calmer_telephony http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/telephony
#src/gz chaos_calmer_management http://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/legacy/packages/management

src/gz chaos_calmer_base file:///home/repo/base
src/gz chaos_calmer_luci file:///home/repo/luci
src/gz chaos_calmer_packages file:///home/repo/packages
src/gz chaos_calmer_routing file:///home/repo/routing
src/gz chaos_calmer_telephony file:///home/repo/telephony
src/gz chaos_calmer_management file:///home/repo/management

run update procedure:

root@OpenWrt:/# opkg update
Downloading file:///home/repo/base/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_base.
Downloading file:///home/repo/base/Packages.sig.
Signature check passed.
Downloading file:///home/repo/luci/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_luci.
Downloading file:///home/repo/luci/Packages.sig.
Signature check passed.
Downloading file:///home/repo/packages/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_packages.
Downloading file:///home/repo/packages/Packages.sig.
Signature check passed.
Downloading file:///home/repo/routing/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_routing.
Downloading file:///home/repo/routing/Packages.sig.
Signature check passed.
Downloading file:///home/repo/telephony/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_telephony.
Downloading file:///home/repo/telephony/Packages.sig.
Signature check passed.
Downloading file:///home/repo/management/Packages.gz.
Updated list of available packages in /var/opkg-lists/chaos_calmer_management.
Downloading file:///home/repo/management/Packages.sig.
Signature check passed.

Now, it is possible to install any additional software we like. For example, let’s install nano text editor:

root@OpenWrt:/# opkg install nano
Installing nano (2.4.1-1) to root...
Downloading file:///home/repo/packages/nano_2.4.1-1_brcm47xx.ipk.
Installing libncurses (5.9-2) to root...
Downloading file:///home/repo/base/libncurses_5.9-2_brcm47xx.ipk.
Installing terminfo (5.9-2) to root...
Downloading file:///home/repo/base/terminfo_5.9-2_brcm47xx.ipk.
Configuring terminfo.
Configuring libncurses.
Configuring nano.

Make sure internet works

If you have access to an internet via LAN cable (i.e. you do have another router running DHCP in your network with internet access), plug your DIR-320 WAN port into your network. Make sure, it gets dynamic IP:

root@OpenWrt:/# ifconfig

br-lan    Link encap:Ethernet  HWaddr 00:90:4C:C0:00:01
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fd47:5a3c:26b2::1/60 Scope:Global
          inet6 addr: fe80::290:4cff:fec0:1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:37 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:3926 (3.8 KiB)

eth0.2    Link encap:Ethernet  HWaddr 00:90:4C:C0:00:01
          inet addr:192.168.0.194  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::290:4cff:fec0:1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:223 errors:0 dropped:0 overruns:0 frame:0
          TX packets:104 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:50169 (48.9 KiB)  TX bytes:9778 (9.5 KiB)

Make sure that your existing network uses different subnet. By default, OpenWRT is configured to use 192.168.1.X subnet, so you should use something like 192.168.0.X or 192.168.2.X. Verify that you’re able to download content from the internet:

root@OpenWrt:/# wget http://httpbin.org/ip -O /dev/null
Connecting to httpbin.org (54.175.219.8:80)
null                 100% |*******************************|    32   0:00:00 ETA

If you’re not able to get any content outside your network, it is most likely a problem with firewall. One of the symptoms of this problem is that when you issue ping command, there will be following output ping: sendmsg: Operation not permitted.

To allow all traffic in any direction(don’t do this in production environment!), do the following:

root@OpenWrt:/# echo "iptables -P INPUT ACCEPT" >> /etc/firewall.user
root@OpenWrt:/# echo "iptables -P OUTPUT ACCEPT" >> /etc/firewall.user
root@OpenWrt:/# echo "iptables -P FORWARD ACCEPT" >> /etc/firewall.user
root@OpenWrt:/# /etc/init.d/firewall restart

LuCI installation

LuCI is a web-based GUI for managing OpenWRT. A lot of essential configuration which is pretty cumbersome to do via command-line could be easily made through LuCI.

Before installing LuCI packages I would strongly suggest setting up kmod-zram and zram-swap packages if you’re not using external HDD swap, but instead rely on slow, error-prone flash memory. Zram is a special linux kernel module which makes part of your RAM compressed and behave like swap.

Now, let’s proceed:

root@OpenWrt:/# opkg update && opkg install --force-overwrite wget ca-certificates coreutils dropbear
root@OpenWrt:/# opkg install ip fdisk usbutils screen htop
root@OpenWrt:/# opkg install luci luci-proto-3g luci-proto-ipv6 luci-proto-openconnect luci-proto-ppp luci-proto-relay

After successfull installation of the above mentioned packages, reboot and plug your linux host into one of the 4 LAN ports of the router. Since LuCI is not yet configured, it is not possible to access it via WAN, therefore we’re going to setup it from the internal router network. Open up your favorite browser and go to http://192.168.1.1/cgi-bin/luci

From now on, you may fully configure your router by setting up root password, enabling Wi-Fi, etc.

3g/CDMA modem configuration

Now, the most interesting part — how do we connect external CDMA modem to the router and make sure it will function as a WAN interface for LAN clients? At the time of this writing, I had in my hands a used Sierra AirCard 250U:

In this part of the article, we’re going to setup it to act as an external WAN interface. First off, disconnect ethernet cable from router’s WAN port and connect modem. Make sure you’re using USB-hub with external power supply, since 3G modems may drain a lot of current from single USB port and you might experience a lot of weird issues.

Open up terminal console using ssh (telnet should be already disabled if you’ve configured router’s root password):

bananos@ubby:$ ssh  root@192.168.1.1
Warning: Permanently added '192.168.1.1' (RSA) to the list of known hosts.
root@192.168.1.1's password:

When CDMA modem is powered on, it is possible to see it in the list of connected usb devices:

root@OpenWrt:~# lsusb
Bus 001 Device 007: ID 1199:0301 Sierra Wireless, Inc.
Bus 001 Device 008: ID 198f:0220 Beceem Communications Inc. BCSM250 WiMAX Adapter
Bus 001 Device 004: ID 0424:2512 Standard Microsystems Corp. USB 2.0 Hub
Bus 001 Device 003: ID 05ac:0221 Apple, Inc. Aluminum Keyboard (ISO)
Bus 001 Device 005: ID 067b:2506 Prolific Technology, Inc. Kaser 8gB micro hard drive
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 002: ID 05ac:1006 Apple, Inc. Hub in Aluminum Keyboard
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

In this example I’m using Apple Keyboard as USB hub :) Aricard 250U may actually work in CDMA/WiMax mode, and is detected as two separate devices Sierra Wireless, Inc. and Beceem Communications Inc. BCSM250 WiMAX Adapter. Now, let’s search for Sierra support in software packages:

root@OpenWrt:~# opkg update
root@OpenWrt:~# opkg list | grep sierra
kmod-usb-net-sierrawireless - 3.18.23-1 - Kernel support for Sierra Wireless devices
kmod-usb-serial-sierrawireless - 3.18.23-1 - Kernel support for Sierra Wireless devices

Luckily, there is kernel support for Sierra devices and we’re going to leverage that! This is exactly the case where modern linux kernel shines in all its beauty. On top of this kernel modules we need to install some other generic stuff:

root@OpenWrt:~# opkg install kmod-usb-serial kmod-usb-serial-option kmod-usb-serial-wwan kmod-usb-serial-ipw
root@OpenWrt:~# opkg install comgt usb-modeswitch coreutils-stty
root@OpenWrt:~# opkg install kmod-usb-net-sierrawireless kmod-usb-serial-sierrawireless
root@OpenWrt:~# reboot

Make sure that sierra kernel support is functioning:

root@OpenWrt:~# lsmod | grep sierra
sierra                  6048  0
sierra_net              5600  0
usbnet                 15872  1 sierra_net

As this point, we have a serial interface to CDMA modem at /dev/ttyUSB0. Verify that modem responds to AT commands:

root@OpenWrt:~# gcom info -d /dev/ttyUSB0
##### Wireless WAN Modem Configuration #####
Product text:
====

Manufacturer: Sierra Wireless, Inc.
Model: AC250U Rev 2.0 (3)
Revision: p3012901,8815 [May 28 2010 14:42:39]
QCOM: SWI6085_FP.01.28
BOOT: SWI6085_PP.01.29.01 2010/05/28 18:13:46
APPL: SWI6085_PP.01.29.01 2010/05/28 18:13:46
USB VID: 0x1199 PID: 0x0301
ESN: 09612160827
0x60B98F3B
+GCAP: +CIS707-A, CIS-856, CIS-856-A, +MS, +ES, +DS, +FCLASS
SKU: 0x132BD1
OK
====
Manufacturer:           ERROR
IMEI and Serial Number: 09612160827
Manufacturer's Revision:
p3012901,8815 [May 28 2010 14:42:3
Hardware Revision:

Network Locked:

Customisation:

Band settings:          (
)
APN:

##### END #####

Now, switch to LuCI and go to Network->Interfaces. Stop WAN6 unless you're going to use IPv6 and edit WAN interface.

When editing existing WAN interface, change Protocol to UMTS/GPRS/EV-DO, click Switch protocol button and wait for additional parameters to appear:

On this screen you should enter provider specific info (take a look at your contract/prepaid plan details). Since my modem is connected to Ukraine's CDMA Intertelecom my connection parameters are:

  • Protocol: UMTS/GPRS/EV-DO
  • Modem device: /dev/ttyUSB0 (we've tested above that it actually responds to AT commands)
  • Service type: CDMA/EV-DO
  • APN: empty
  • PIN: empty
  • PAP/CHAP username: IT
  • PAP/CHAP password: IT
  • Dial number: #777

Note, that your interface will now be named 3g-wan and since there is a flag called Bring up on boot in the Advanced tab your CDMA connection will be established automatically on power up. To make sure that everything works, open up terminal once again:

root@OpenWrt:~# logread | grep -E "chat|ppp"
Tue Apr  5 19:38:31 2016 daemon.notice pppd[6810]: pppd 2.4.7 started by root, uid 0
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (BUSY)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (NO CARRIER)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (ERROR)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (NO DIAL TONE)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (NO ANSWER)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: abort on (DELAYED)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: report (CONNECT)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: timeout set to 10 seconds
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: send (AT^M)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: expect (OK)
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: AT^M^M
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: OK
Tue Apr  5 19:38:32 2016 local2.info chat[6821]:  -- got it
Tue Apr  5 19:38:32 2016 local2.info chat[6821]: send (ATZ^M)
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: timeout set to 30 seconds
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: expect (OK)
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: ^M
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: ATZ^M^M
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: OK
Tue Apr  5 19:38:33 2016 local2.info chat[6821]:  -- got it
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: send (ATDT#777^M)
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: expect (CONNECT)
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: ^M
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: ATDT#777^M^M
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: CONNECT
Tue Apr  5 19:38:33 2016 local2.info chat[6821]:  -- got it
Tue Apr  5 19:38:33 2016 local2.info chat[6821]: send (^M)
Tue Apr  5 19:38:33 2016 daemon.info pppd[6810]: Serial connection established.
Tue Apr  5 19:38:33 2016 daemon.info pppd[6810]: Using interface 3g-wan
Tue Apr  5 19:38:33 2016 kern.info kernel: [ 8554.840000] 3g-wan: renamed from ppp0
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: Connect: 3g-wan < --> /dev/ttyUSB0
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: PAP authentication succeeded
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: local  IP address 10.227.181.163
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: remote IP address 172.17.4.100
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: primary   DNS address 192.168.4.3
Tue Apr  5 19:38:33 2016 daemon.notice pppd[6810]: secondary DNS address 192.168.4.7
Tue Apr  5 20:08:32 2016 daemon.info pppd[6810]: LCP terminated by peer
Tue Apr  5 20:08:32 2016 daemon.info pppd[6810]: Connect time 30.0 minutes.
Tue Apr  5 20:08:32 2016 daemon.info pppd[6810]: Sent 826328 bytes, received 547992 bytes.
Tue Apr  5 20:08:33 2016 daemon.info pppd[6810]: Terminating on signal 15
Tue Apr  5 20:08:35 2016 daemon.notice pppd[6810]: Connection terminated.
Tue Apr  5 20:08:36 2016 daemon.notice pppd[6810]: Modem hangup
Tue Apr  5 20:08:36 2016 daemon.info pppd[6810]: Exit.
Tue Apr  5 20:08:37 2016 daemon.notice pppd[7884]: pppd 2.4.7 started by root, uid 0
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (BUSY)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (NO CARRIER)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (ERROR)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (NO DIAL TONE)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (NO ANSWER)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: abort on (DELAYED)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: report (CONNECT)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: timeout set to 10 seconds
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: send (AT^M)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: expect (OK)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: AT^M^M
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: OK
Tue Apr  5 20:08:38 2016 local2.info chat[7896]:  -- got it
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: send (ATZ^M)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: timeout set to 30 seconds
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: expect (OK)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: ^M
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: ATZ^M^M
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: OK
Tue Apr  5 20:08:38 2016 local2.info chat[7896]:  -- got it
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: send (ATDT#777^M)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: expect (CONNECT)
Tue Apr  5 20:08:38 2016 local2.info chat[7896]: ^M
Tue Apr  5 20:08:39 2016 local2.info chat[7896]: ATDT#777^M^M
Tue Apr  5 20:08:39 2016 local2.info chat[7896]: CONNECT
Tue Apr  5 20:08:39 2016 local2.info chat[7896]:  -- got it
Tue Apr  5 20:08:39 2016 local2.info chat[7896]: send (^M)
Tue Apr  5 20:08:39 2016 daemon.info pppd[7884]: Serial connection established.

These are the logs from pppd daemon and CHAT script, responsible for sending AT commands to modem. As you can see there may be random hangups, but the connection is automatically re-established which is very nice.

And when you enter ifconfig command you should see 3g-wan interface too:

root@OpenWrt:~# ifconfig
3g-wan    Link encap:Point-to-Point Protocol
          inet addr:10.227.196.50  P-t-P:172.17.4.100  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:977 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2117 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:529666 (517.2 KiB)  TX bytes:324250 (316.6 KiB)

In case you’re interested in diving deeper into how things work, I’d recommend looking at these files:

  • /etc/config/network contains network configuration
  • /lib/netifd/proto/3g.sh shell logic responsible for running pppd daemon

Measuring signal strength

The last problem you’ll probably stumble upon — is how to measure signal strength, especially if you’re setting up standalone solution at a remote location with a modem connected to an external antenna. This is usually accomplished by sending special AT command to modem. Note, however, that most software and examples over internet are targeted towards more popular GRPS/UMTS modems, and they will probably won’t work.

Before using serial protocol to communicate with modem, we must shutdown existing 3g-wan connection, because otherwise we’ll get cat: read error: Resource temporarily unavailable:

root@OpenWrt:~# ifdown wan

Note, that ifdown won’t accept 3g-wan as interface, but oddly enough the above command works. For now, let’s focus on how to send AT commands to modem:

  • run screen
  • open 2 consoles

In the first console run cat /dev/ttyUSB0 (this is a place to look for modem replies) and in the second run echo -ne "at!status?\r\n" > /dev/ttyUSB0. Switch back consoles and you should see something like this:

root@OpenWrt:~# cat /dev/ttyUSB0
at!rssi?
-83

OK

A range from -60 dbm to -90 dBm is considered adequate. Using this special AT command you may now run it in a loop with small delay, observe signal strength in the second console and properly adjust external antenna. Also, there seems to be an unofficial OpenWRT package specifically for signal monitoring called 3ginfo, but I’ve not tried it and not sure if it works for CDMA/EVDO modems.

TL;DR;

Seriously, If you want to avoid all the hassle of setting up CDMA modem and OpenWRT, just buy yourself a device which combines WiFi router and 3g modem — MiFi will do just fine :)

Download openwrt-15.05.1-brcm47xx-legacy-asus-wl-500gp-v2-squashfs.trx (MD5: 420e24e9a042c01585d818c14afa11d3)

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