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No IP address via DHCP

Former Member

Hello everyone,

 

I have got two PI’s two weeks ago and yesterday tried to get Ethernet working.

Fresh raspbian OS is used.

I am using a cable modem that is DHCP capable (my laptop gets dynamic IP without problems). Ethernet cable is also fine – tried with the laptop.

Connecting it to PI and booting, I see the “link” light and “100” light ON.

The IP address is not available.

I checked /etc/network/interfaces:

auto lo

 

iface lo inet loopback
iface eth0 inet dhcp

 

Tried to change to:

 

auto eth0
iface eth0 inet dhcp

 

Did not help also.

 

On the booting log I see:

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 12

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 5

5-6 such messages, then:

No DHCPOFFERS received

 

I tried to reduce power consumed by PI (took away the USB mouse and keyboard), did not change anything. I am using 5V 1A power supply.

 

Any idea what the problem might be?

Parents Reply Children
  • in reply to wallarug

    No, it is the modem/switch.

    What confused me, that I tried to boot PI connecting it directly to the cable modem and it did not get any IP. I forgot that the IP given before to my laptop, is kept for a while and new IP was obviously not given.

    Power cycle of the cable modem and connecting a PI directly to it or via switch, solved the problem, it got IP. Laptop connected after this, did not get an IP...

    So in reality it is a problem of the cable modem/switch – only one IP via DHCP.

    I have used this switch with several PC those had static IPs and is surprised it does not work with DHCP.

     

    I have a monitor connected to PI.

    One can change raspi-config or /etc/network/interfaces and reboot. The same effect.

  • in reply to Former Member

    From your decription, you have a cable modem *not* a gateway/router.  For multiple devices to be connected at the same time, you need to have a gateway or router to nat one of the private networks (10.x.x.x/192.168.x.x/172.16.x.x) to the public address you get from the cable modem.  Sometimes the modem/router is combined into a single device.  Provide (or google) the model number of your cable modem to find out if it is a gateway/router or modem.  The most common private range used is 192.168.1.x or in CIDR format 192.168.1.0/24.  It is also possible that you have a gateway but it's configured to only serve up one IP address.  This is sometimes done by providers as a security feature.  If this is the case and you have access to the configuration ui of the cable router, then you should see if the lan dhcp configuration has a limit of number of addresses set to 1.  Good luck.

  • in reply to Former Member

    Yes it's certainly a god starting point to get a cheap router and put it in front of the network between the the Cable device and you.

    They are readily available for £10-20 range.  At least then you can work from a know good situation !