Test Network Configuration

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Contents

Questions

  • Is the XO connected to Link-local or a mesh?
  • Is it connected to an MPP? (Depreciated; no longer available)
  • Is it connected to the Internet?
  • Is it connected to a Jabber (XMPP) server?
  • What is the IP address?

Layer 2

The wireless configuration of the network can be examined using the iwconfig eth0 command. We get MAC layer information such as

  1. ESSID
    • olpc-mesh : Indicates a mesh with or without Internet connectivity
  2. Mode
    • Managed : It is an Access Point(AP) configuration
    • Ad-hoc : It is a mesh configuration (no infrastructure)
  3. Frequency (MHz)
    • 2.412 : Channel 1
    • 2.437 : Channel 6
    • 2.462 : Channel 11
    • Channels 1,6, 11 can be used to join a Link-local mesh
    • Channels 1, 6, 11 can also be a School server mesh (ch 1 is almost always on at OLPC offices)
    • At OLPC offices, '802.11 Media lab' AP operates on Channels 6 and 11
  4. Cell/AP Mac
    • Access Point : The AP's MAC
    • Cell : A virtual 02:xx:xx:... MAC address assigned by the some mesh points. It indicates mesh configuration

Layer 3

IP addresses

The network layer information can be observed with ifconfig. The default built-in wireless adapter provides an Ethernet interface eth0, and a mesh interface msh0. Connecting additional 802.11s adapters will introduce additional pairs of eth1,eth2,.. and msh1,msh2,.. interfaces. Connecting Ethernet adapters will introduce additional eth1,eth2,.. interfaces, and will provide Ethernet connectivity. In the default case(although the same applies for all) the interfaces provide the following IPv4 addresses

  • eth0
    1. Connected to an AP without NAT
      • any public address(18.85.x.x when connected to Media Lab 802.11 at OLPC offices)
    2. Connected to an AP, but behind a NAT
      • 192.168.x.x
      • 172.x.x.x
      • 10.x.x.x
    3. Connected to a switch with no gateway
      • 169.254.x.x
    4. Not connected to an AP
      • blank
  • msh0
    1. Link-local
      • 169.254.x.x
    2. Connected to an MPP
      • 169.254.x.x
    3. Connected to a School server
      • 172.x.x.x (172.18.x.x when connected to the School server in OLPC offices)
      • 192.168.x.x
      • 10.x.x.x
    4. Connected to an AP via wireless or Ethernet adapter
      • 169.254.x.x
      • none

It is interesting to note that the 169.254.x.x address when applicable are always the same by default. If no address shows in the msh0 you can

killall dhclient
dhclient           # Send DHCP request to force (if possible) to acquire a connection to a gateway

avahi-autoipd      # If no mesh gateway is available (MPP or School server) it will assign a zeroconf address(169.254.x.x)

DNS check

The most direct way to check Internet connectivity is by checking the resolv.conf file. It shows if the XO is registered to a DNS server. It can be viewed with,

cat /etc/resolv.conf
  1. If it is empty,
    • No connection to the Internet (technically, no connection to the DNS server).
  2. If it includes a nameserver with private address (172.x.x.x, 169.168.x.x, 10.x.x.x),
    • Connected to an AP behind a NAT,
    • Connected to an MPP, which connects to an AP behind a NAT,
    • Connected to a School server (172.18.0.1 for the School server in OLPC offices, although others are also available).
  3. If it includes a nameserver with public address,
    • Connected to an AP without a NAT,
    • Connected to an MPP, which connects to an AP without a NAT.
  4. The is a rare possibility resulting from a NetworkManager failure, of an XO to have access to the Internet, but the resolv.conf to be blank. In that case, the XO will not be able to resolve hostnames. This possibility can be examined with,
ping www.mit.edu   # No replies
ping 18.7.22.83    # Normal replies  

The general rule of thumb regarding the resolv.conf file in the lab XOs is the following:

  • empty: Link-local
  • 172.18.x.x: Schoolserver
  • 18.85.x.x: Media lab AP

If the XO connects to a channel that includes a School server or an MPP, but for some reason there is no Internet connectivity, and the resolv.conf file is empty, check if it is forced in Link-local or another configuration,

nano /etc/NetworkManager/mesh-start # confirm that the file is empty(if it exists)

If the problem persists you can try,

killall dhclient
dhclient           # Send DHCP request to force(if possible) to acquire a routable IP

Telepathy services

The Presence Service acquires information on other XOs in the network, and provides the capability to view them in the Neighborhood view, or share with them an activity. This is achieved through two child telepathy services, Salut and Gabble.

Salut

Salut runs when the XO is connected to a mesh. It uses the avahi _presence._tcp service. All XOs in the same mesh identify themselves in the Neighborhood view through Salut. They can be examined through,

avahi-browse -t _presence._tcp

Jabber

Gabble will allow XOs that belong to different geographical locations to communicate with each other. It will detect Internet connectivity and connect to a Jabber server. All XOs connected to the same Jabber server will appear to the Neighborhood view. The currently possible servers are

jabber.sugarlabs.org
jabber.laptop.org
olpc.collabora.co.uk
  • By build 616, the Presence Service does not allow Gabble and Salut to run simultaneously.
  • It constantly checks whether there is Internet connectivity, and switches from Salut to Gabble accordingly.
  • The XOs displayed in the Neighborhood view either belong to the mesh, or the Jabber server, not both.
  • The Internet connectivity does not work very accurately. It is very common when connected to the School server, which provides connectivity, that the XO is running Salut. However, it is convenient in the sense that it can now share activities with others in the mesh.

Detecting which service is running

  • The simpler way to detect whether Salut or Gabble is running is by observing the Neighborhood view. If you see XOs that you haven't seen in the lab, then you are probably running Gabble.
  • It can also be checked from the Analyze Activity - Interfaces tab - Presence Service - Buddies list - Handles column. The entries either start with ../gabble/jabber/.. or ../salut/local-xmpp/...
  • To confirm you are running Gabble you can check the config file for the [Server] (not Jabber) entry to be true. This, however, can be misleading, because the file doesn't update properly when you disconnect from the Jabber server. Thus, it usually includes obsolete information.
$ cat /home/olpc/.sugar/default/config
...
[Server]
registered = True             # running Gabble
server = jabber.laptop.org  
  • The console provides a more efficient way of determining with confidence which service is running. The process list will include either a telepathy-salut or a telepathy-gabble process,
ps ax                         # general process list
ps U olpc -f|grep telepathy   # only the required entry will be displayed
  • The Jabber server to which the XO is connected (if it's running Gabble) can be examined using the netstat command,
netstat -tpT|grep telepathy   # the connection established by the telepathy-gabble process

Combine the tests in an automated script

All the above tests require checking many different locations and running several commands. Alternatively, you may run olpc-netstatus from the Terminal Activity or a console. It will accumulate and display the following network overview directly. This is a case of an XO connected to the School server on Channel 1.

$olpc-netstatus

Model     : C2
Serial    : CSN74400049
MAC       : 00:17:C4:0C:CD:11

Build     : update.1 703
Firmware  : CL1 Q2D14 Q2D
Libertas  : 5.110.22.p1 

Nick      : W03
Uptime    : 01:12:06

IP eth0   : 172.18.0.250
IP msh0   : 169.254.5.77
DNS       : 172.18.0.1

Telepathy : gabble    
Jabber    : schoolserver.laptop.org
XOs       : 4

Essid     : olpc-mesh
Channel   : 1

School    : schoolserver.laptop.org
Config    : School Mesh

More up-to-date version of olpc-netstatus, and other useful Network tools are available at Network Resources.

Useful locations

You may need to be root to access some of these files

/etc/resolv.conf
DNS server
/etc/dhcpd.conf
check whether the XO acts as an MPP
/etc/NetworkManager/mesh-start
used to force a lower priority network configuration
/home/olpc/.sugar/default/config
user information
/home/olpc/.sugar/default/nm/networks.cfg
stores access points information, such as WEP password
/var/log/messages
main log file, may hold messages from NetworkManager
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