RE: Assigning Multiple IP's with PPPoE

I wasn't at my main PC. More details on my items 2 and 3 are below. Excuse the context of the details as it is from some material I wrote regarding DSL routers.

A DSL router might issue a DHCP Inform message (DHCPINFORM) as identified in RFC 2131 ("Dynamic Host Configuration Protocol") to identify the subnet associated with the router using the "Subnet Mask" vendor extension identified in RFC 2132 ("DHCP Options and BOOTP Vendor Extensions"). The DSL router might then use this information establish IP addresses to pass to the LAN devices on the router.

Alternately a DSL router might act as a DHCP Relay Agent or issue a DHCP request, potentially in combination with a specified subnet (RFC 3011, "The IPv4 Subnet Selection Option for DHCP"), when a LAN devices requests an IP address.

In the PPP world (PPPoE) the ability exists to pass the subnet information to the customer's equipment during PPP negotiation. The equipment then uses this to establish DHCP information to assign to local devices on the LAN. The subnet information exchange occurs during IPCP subnet negotiation.

A protocol extension was developed and proposed to pass the subnet mask (draft-heinanen-ppp-subnet-00.pdf which was re-released as draft-helenius-ppp-subnet-00.txt, "PPP Internet Protocol Control Protocol Extensions for IP Subnet"). The PPP subnet extension was intended as a way to populate a LAN-side DHCP server address range. What was not considered at the time were implementations using this with NAT in which LAN and WAN side networks were not one in the same.

The draft died after the authors received negative and sometimes hostile feedback persuading them to give up the IETF track. The PPP development community felt that since PPP was a point to point protocol, extensions to address items outside of the point to point contact shouldn't be in PPP. For some reason, they didn't feel this way originally when DNS server and WINS server information was added to PPP standards.

Even so, a number of vendors have implemented a PPP IPCP subnet feature. It is believed that this is not implemented as defined in the draft but rather using RFC 2153. This may be implemented as a non-approved PPP IPCP option using option code 144, the length of the option being 6 and the mask being expressed as a 32-bit mask (e.g. 0xFFFFFF80), not as a number indicating the consecutive number of 1s in the mask (from 0 to 32). This is partially documented in "T1: A Survival Guide" (Matthew S. Gast, O'Reilly & Associates, September 2001).

This feature is thought to be implemented in a number of products. A partial list of the vendors or products is:

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DSL End User Router Providers:
- Alcatel Speed Touch 510/520 series products (using release 3.7 or
later)
- Cisco 67x CPE products (using CBOS 2.1.0)

• Cisco DSL routers (82x, 806, SOHO 7x using IOS 12.2(1)XD1)
• Cayman Systems (2E, 3220 models, using "set ip ip-ppp ipcp-subnet")
• Netopia (R-Series routers, using firmware 4.8.3)
• Efficient (using "remote setipoptions lanconfig")

DSL B-RAS Providers:
- Cisco 6400 NRP (IOS 12.0(5)DC, 12.1(3)DC and 12.1(5)T)

• Cisco 7200 (IOS 12.1(3)T)
• Nortel (Shasta SSG 5000)

I have asked a number of vendors for details of the actual implementation. They claim they would get me the details (1 CTO, 1 design manager and varous sales teams) and none have come through.

-----Original Message-----
From: MULTACH, JEFF (SBC-MSI)
Sent: Wednesday, September 24, 2003 6:25 PM To: 'Matt'; pppoe@ipsec.org
Subject: RE: Assigning Multiple IP's with PPPoE

Some alternatives. All dependent on the capabilities of your PPPoE server.

• Use multiple PPPoE sessions
• Run DHCP afterwards to pick up additional IP addresses
• Utilize IPCP subnet negotiation, a non documented solution, to pass a subnet to the PPPoE client.