Network connection diagnostics

On 18 Sep 2006 23:05:50 -0700, "Marco A. Cruz Quevedo"

ifconfig -a shows interfaces (NICs or "adapters"), including their IP if they have one. route -n shows the routing table, including the default route if there is one, which default route contains the gateway address. For example, below, the eth0 NIC's IP is 192.168.3.12. If that line is missing your NIC lacks an IP. And the gateway address is 192.168.3.2. The default route is the route to "0.0.0.0" and you see that address in that route's line item in the table. Maybe your service network restart is triggering an address request (ie running a dhcp client), but that's not taking place as part of the boot process. Checketc-sysconfig-network for something like ONBOOT=no (or yes). If it's no, it's configured to omit setting up network stuff as part of booting. Check also for something like BOOTPROTO=dhcp (I think) to see whether, when the network config is performed it entails use of dhcp. To experiment with running dhcp client manually, the name of the client is usually dhclient, otherwise there's one called pump and one called dhcpcd. Your system might have one or another of those.

Example: eth0 Link encap:Ethernet HWaddr 00:02:B3:41:86:F9 inet addr:192.168.3.12 Bcast:192.168.3.255 Mask:255.255.255.0 inet6 addr: fe80::202:b3ff:fe41:86f9-64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:8038 errors:0 dropped:0 overruns:0 frame:0 TX packets:5327 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000

Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.3.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 0.0.0.0 192.168.3.2 0.0.0.0 UG 0 0 0 eth0