Advanced Networking

Overview

There are many thing that GWS(The Configuration Software for Telem-GW6) can't do. For instance NTP, VLAN and OpenVPN configuration. If something extra is needed then in general user's should create Linux scripts and copy them to Telem-GW6. Sometimes a change of an existing script is enough. Example scripts can be found from Telem-GW6 /usr/local/bin/ folder.

Location of Startup Scripts

/etc/init.d/

Scripts in this folder are run at system startup.

/etc/network/if-ud.d/ and /etc/network/if-down.d/

Scripts in this folder are run when an interface(for instance ethernet interface eth0) becomes available or unavailable. These scripts are needed(used) for instance for configuring the firewall or routing.

/etc/ppp/ip-up or /etc/ppp/ip-down

Scripts in this folder are run when an PPP interface becomes available or unavailable. These scripts are needed(used) for instance for configuring the firewall or routing.

Examples

A good example that is in use in production systems is NTP or PPP. Both are located at /usr/local/bin.

VLAN

For instane a script like this:

# Script to show creation of VLAN's
# Copy it to /etc/network/if-up.d and change file permissions to make it executable.
if [ "$IFACE" == "eth0" ]
then
    logger "vlan_enable for interface:$IFACE"

    # So that from ifconfig we see vlan30 not eth0:30
    vconfig set_name_type VLAN_PLUS_VID_NO_PAD

    # If vlan 30 exists remove it
    vconfig rem vlan30

    # Create vlan 30, with vlan id of 30
    vconfig add eth0 30

    # Set ethernet priorities
    vconfig set_egress_map vlan30 0 7
    vconfig set_ingress_map vlan30 0 7

    # Bring new network interface up, that is make it ready for new connections
    ifconfig vlan30 172.22.101.196 netmask 255.255.255.240 txqueuelen 1000 up

    # Add entry to routing table, 172.22.101.193 is router at vlan 30
    route add default gw 172.22.101.193 vlan30
fi

makes a single VLAN called vlan30.

Troubleshooting

For troubleshooting:

• tcpdump [1]: A powerful command-line packet analyzer.

root@telem-gw6-com8$ tcpdump --help
tcpdump version 4.1.1
libpcap version 1.1.1
Usage: tcpdump [-aAbdDefIKlLnNOpqRStuUvxX] [ -B size ] [ -c count ]
		[ -C file_size ] [ -E algo:secret ] [ -F file ] [ -G seconds ]
		[ -i interface ] [ -M secret ] [ -r file ]
		[ -s snaplen ] [ -T type ] [ -w file ] [ -W filecount ]
		[ -y datalinktype ] [ -z command ] [ -Z user ]
		[ expression ]

• netstat [2]: Is a command-line tool that displays network connections.

root@telem-gw6-com8$ netstat --help
BusyBox v1.17.4 (2011-10-17 18:03:09 EEST) multi-call binary.

Usage: netstat [-laentuwxr]

Display networking information

Options:
	-l	Display listening server sockets
	-a	Display all sockets (default: connected)
	-e	Display other/more information
	-n	Don't resolve names
	-t	Tcp sockets
	-u	Udp sockets
	-w	Raw sockets
	-x	Unix sockets
	-r	Display routing table