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New Contributor III

1335 Fails to Get DHCP From Arris Modem

I'm attempting to connect a NV 1335 to a Charter/Spectrum cable modem Arris Tm1602.  This is just a modem, not a router, so there are no settings in it.  I previously had a Netgear router connected to the modem, and it retrieves the dynamic IP from the modem just fine.  I then reboot the modem, connect the 1335, and it will never get an IP address. 

  • Rebooting and reconnecting the Netgear or a laptop will retrieve an IP address, so I know the modem is working.
  • Plugging the designated WAN port from the 1335 into a LAN port on the Netgear will retrieve an IP address, so I know my config on the 1335 is working.

A couple of interesting things:

  • This modem allows access for viewing of status on a local IP, 192.168.100.1, though you can't change any settings.  This in spite of the fact that when you connect to it via a laptop, you are assigned the external IP.
  • On rare occasions of rebooting one, then the other, modem and 1335--I tried for hours yesterday--I did get it to show an IP in the AOS web GUI of 192.168.100.x (it varied), but it never showed Bound.

When I ran "debug ip dhcp client vlan 2", it showed that the DCHPDISCOVER would be sent, but the DHCPOFFER would never be received.  Then when I plugged it into the Netgear, it did receive the DHCPOFFER and the rest of the negotiation.  I never caught the times it got a 192.168.100.x, but I assume it got the offer but not the rest of the negotiation.

The question is, based on the apparently odd way the Arris modem is set up, is there something I can change in the 1335 setup to accommodate this and make the DHCP work?

Relevant config snippet:

interface gigabit-switchport 0/1

  no shutdown

  switchport access vlan 2

!

!

interface vlan 2

  description Public

  ip address dhcp

  ip mtu 1500

  ip access-policy Public

  ip crypto map VPN

  qos-policy out vlan2QosWizard

  no awcp

  no ip route-cache express

  no shutdown

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