Restricting ONT's Ethernet port to singe active IP

Frank Bulk frnkblk at
Thu Apr 23 18:26:35 UTC 2009

You'd only get a cookie if you were the first to answer.  Others have chimed
in first. ;)


-----Original Message-----
From: dhcp-users-bounces at
[mailto:dhcp-users-bounces at] On Behalf Of Marc Perea
Sent: Thursday, April 23, 2009 9:01 AM
To: dhcp-users at
Subject: Re: Restricting ONT's Ethernet port to singe active IP

>But an RFC-1483-like FTTH implementation doesn't come with all those
>benefits.  We could put a $50 CPE in each home with PPPoE and be
>for managing it, but we would prefer to let customers plug in their own
>equipment into the ONT, but just get one IP address.
>Option 82 support seems like the closest way to get it done, by creating
>classes and handing out an static IP, but I understand the process
>correctly, it requires generating a class for each Option 82 string and
>assigning a static IP address.  That has the negatives of creating classes
>in advance and giving out statics when I don't want to give out statics.

This is what we decided to do - be responsible for the first L3 device at
the premise, and we went with statics for each class, one class per
agent.circuit-id. We like having a static IP dynamically assigned. It was a
hassle initially getting the syntax of the CID string formalized, but now
it's really not a big deal.

>What it seems I want is to be able to use dynamic classes and hand out just
>one IP address for each Option 82 string.  I know that dhcp is built around
>using the MAC address as the standard identifier, but is there any
>to the challenge we're facing?

So I haven't tried this, but couldn't you use subclasses to do this? In the
past we've used the spawn with option in order to have multiple classes of
service - like 1 IP, 5 IP, 10 IP, etc. Something like:
subnet x.x.x.x netmask y.y.y.y {
  pool {
    class "customers" {
      match if exists agent.circuit-id;
      spawn with option agent.circuit-id;
      lease limit 1;

>We also want our customers to be able to change CPE half-way through a
>and not have to call the helpdesk to flush their legacy DHCP leases because
>their new CPE doesn't get an IP address. ;)

We haven't got a solution for this. You can set lease times low, which is
probably undesirable. For us, a help desk call is necessary if you don't
want to wait out the lease. If anyone has another idea here, I'd be glad to
hear it.

>I'm open for suggestions, and for those who can design an elegant solution
>that doesn't require any re-compiling of code, a bounty.

Do I get a cookie?

Marc Perea
Network Support Engineer
SRT Communications, Inc.
marccp at

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