[Novalug] route not set up on eth0

Peter Larsen peter@peterlarsen.org
Wed Dec 21 22:56:33 EST 2016

On 12/21/2016 05:02 PM, Walt Smith wrote:
> The wireless 4 port switch  had some kind of problem not
> obvious to me.  On the CentOS6, at the end of eth0,  the
> 4 port switch/router would not respond with a
> general route of using ping. 

As I've explained a few times here in the group and in private, this
makes no sense!!  You're NOT routing when accessing a subnet to which
you belong. At least not in the sense you've described. The fact that
your ARP is working means you have connection to this line, and it means
your "route" is working. All the route is doing is telling the OS that
all IP traffic to 192.168.1/24 is to be passed to eth0. The rest is up
what's on the other end of that cable.

A route problem would be that traffic is sent to the wrong interface and
hence gets lost.

So I again ask you to restate the problem. If you are unable to ping a
static IP on a router, based on your own static IP setup, you'll start
by verifying the setup on both sides. So far, I've not seen a single
post where you dump the setup on the router - you just keep telling that
it's on IP - but you never mention subnet or anything else.

For consumers, this is pretty straight forward. They take their router,
plug in a power cable, and a single RJ45 into the "client" side of the
router, and the other end of that cable into a NIC in the computer. Turn
on the router and b y default, the computer will use dhcp on the
interface if properly installed, and hence the computer will get all the
correct settings for IP, network, gateway etc. That of course assumes
the consumer doesn't have any other networks connected.  But I would
start there and simplify.

To have two systems talk to one another via layer 3, they MUST be in the
same subnet. Without that prereq nothing else will work.  Then there are
firewalls and other mechanisms that control what a node/device should
respond to. Generally speaking, a default router should NOT firewall
anything but it's always good to verify. A firmware reset will
definitely take care of this. And note, you can have firewalls on BOTH
sides here which may block ICMP and other protocols.

Here's what I would do:

1) Drop your modem connection
2) Connect your PC to the router using a simple cat5 cable, and plug it
into the "client" port on the router (not the uplink).
3) Perform a firmware reset of the router (assuming you're the only one
connected to it)
4) Enable dhcp on your PC - this is DEFAULT - just make sure
BOOTPROTO=dhcp in /etc/sysconfig/network-scripts/ifcfg-eth0 - reset your
network service and the rest is automatic. You should get an IP address,
and you should be able to ping the router. Or using nmcli: nmcli c
modify eth0 ipv4.method dhcp
5) Once you have it pinged, head to a browser and hit the IP of the
router using just http - that will get you a username/password prompt -
and your manual will tell you what the default user/password is. Login
and check the parameters.

If you're having problems with this setup, it's something physical. If
you cannot reset the firmware, then it's most likely because you don't
have the right information about the setup of the router.

Once you're at this point, you can start making things more complex like
using PPP and your router at the same time, or if you insist change the
defaults for the network parameters on the gateway - make those, test
them before you connect your PPP etc. The only thing activating PPP will
do after you've setup your eth0 address with dhcp is overwrite your
default gateway and DNS. Most likely that's what you want anyway so you
can browse the internet etc.

NOTE - eth0 is a WIRED connection. If you have a wireless router, you
cannot use your wired connection to connect to wireless devices UNLESS
they're already associated with the router and connected with an IP. The
Wireless Router (AP) is NOT a client - it's a server.

  Peter Larsen

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