If I have a firewall connected directly to my cable modem, what traffic do I need to allow it to send and receive in order for it to obtain an IP address via DHCP?

If you wish to filter traffic entering or leaving your firewall from the cable network, you must take care to allow the DHCP messages to and from the PenTeleData DHCP server. When a host requests an IP address via DHCP, it uses UDP port 68 as the source port and UDP port 67 as the destination. When the server replies, it uses UDP port 67 as the source port and UDP port 68 as the destination. PenTeleData recommends that, at a minimum, you configure your firewall to allow DHCP messages to be sent to and received from any host. You can further restrict DHCP traffic by examining your firewall logs to determine specific source and destination IP addresses for the DHCP messages.

I require an IP address that will remain the same (static) for my account. How does this work when I am obtaining an IP address from PTD automatically?

Once an IP address is assigned to your account, that same IP address will be assigned to you automatically whenever your modem comes online. Please note though that there are cases beyond PenTeleData's control where a new IP address may need to be assigned to your account in order to accommodate network upgrades. PenTeleData will always strive to give advanced notice when such a change is required. Please note, "static" IP addresses are only available with PenTeleData commercial broadband accounts.

Does this apply to additional subnets which may be routed to my connection?

No. Such IP addresses will be routed directly to a router connected to your cable modem. Those IP addresses can then be assigned manually or automatically on your LAN. The router interface that connects to your cable modem must still obtain its IP address automatically from PenTeleData. Please note that additional subnets are only available with PenTeleData commercial broadband connections.

Which of my devices do I need to configure for DHCP?

Any device which will be connected to your cable modem directly or through an Ethernet switch should be configured for DHCP. Devices behind a broadband router, such as those made by Linksys or Zyxel, can be configured manually.

Why does PenTeleData require all commercial Cable/DOCSIS Broadband Internet Access users to set their equipment to obtain an IP address automatically (DHCP)?

This requirement is primarily a security measure. Requiring the use of DHCP for IP address assignment prevents things like:

  • A malicious user stealing the IP address of another user with the intent to deny that user service or masquerade as that user online.
  • A malicious user using an unassigned IP address in order to conceal his identity when engaging in activity like hacking or spamming.
  • A user misconfiguring other settings which are defined by DHCP, such as the domain name servers (DNS) they should be using.