Overcoming Networking Problems with a 3Com HomeConnect Dual Link ADSL Modem

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Here's my story of setting up a simple Home Network, which is finally working in spite of 3Com's HomeConnect Dual Link ADSL Modem. Actually, I have a love/hate relationship with the Dual Link. I love the modem's flexibility, and I hate the fact it was incompatible with many home routers until early 2001. Thankfully many of the router vendors are now supporting the Dual Link (checkout Quick Solutions below).

SMOOTH SAILING: Did you install the 3Com Dual Link as PPPoE or Bridged/1483? Then there are NO issues with connecting a router between Dual Link and PCs.

CHOPPY WATERS: Does your ISP use the PPP over ATM (PPPoA) protocol? Then protecting and sharing your Internet connection with a home router/gateway/firewall will be a problem. This is true for Dual Link firmware version 1.0.14, and I haven't seen any firmware updates on the 3Com website (last checked May 7, 2001).

PPPoA: The "Problem Protocol" for LANs

PPPoA is a "problem protocol" for your LAN because it can't be used over standard Ethernet connections. To enable Ethernet-based LAN connections, the Dual Link converts PPPoA on the ISP side of modem into "PPPoE:3com" on the LAN side of modem. Why? Without converting the packets, your computer would need an ATM network interface card instead of an Ethernet interface. However, PPPoE:3com is a non-standard implementation of PPPoE (per IETF RFC2516), and that raises interoperability issues with routers and PPPoE client software (if you don't have a router).

Other ADSL modem vendors chose different approaches to converting the "problem protocol" into an Ethernet compatible protocol. These other approaches have few or no interoperability issues. For example, Alcatel STH converts PPPoA into PPTP (and most consumer routers support this standard), Cisco consumer modems terminate the PPPoA session and act as a gateway/router, and PairGain Megabit modems also use the gateway/router approach.

GUIDE TO HOME NETWORKS SECTION OF WEBSITE: This page outlines quick solutions and then discusses the incompatibility issue in more detail. I've added other pages on securing my Dual Link, configuring my RT314 router, and setting up my LAN. Hope you learn something useful for your own home network!

Quick Solutions for Popular Home Routers:

Just want to get your router setup? Here is the scoop.

Routers from Netgear, Zyxel, Linksys and SMC have firmware that supports PPPoE:3com. I've personally tested all the firmware except Linksys. However, I have received emails from Linksys owners that are successfully using those routers with the Dual Link operating in PPPoA mode.

REQUIREMENTS

1. Verify again that your ISP uses PPPoA (PPP over ATM) to your modem. If yes, continue. If no, this information doesn't apply to you. 

2. I assume you have already configured the 3Com Dual Link and have a working Internet connection. If not, please do that before attempting to configure the router. Follow the install, pick "Other ISP", and be sure to pick PPPoA when prompted.  Behind the scenes, the 3Com installer will configure the Dual Link for PPPoA operation and set PPPoE Service Name to ISP. This is important, as you need to match the modem's "Service Name = ISP" setting with the router's PPPoE Service Name setting (see step 3 below).

3. Verify and/or install router firmware that supports PPPoE:3com (3Com's non-standard dialect of PPPoE). See below for firmware versions.

4. Configure router for PPPoE, and make sure router's "PPPoE Service Name" option is set to "ISP" (without the quotes). This is critical because Dual Link CD-ROM installation configures the modem's internal PPPoE server with "Service Name" set to ISP.

FIRMWARE SUPPORT

Linksys beta firmware v1.38.4c and only this version supports the Dual Link's PPPoE:3com. Set "Host Name = ISP" which is the first field on the Setup menu tab. The Dual Link is only supported in v1.38.4c and is not supported in other firmware versions. Checkout this link  for details:
http://www.dslreports.com/forum/remark%2c651534%3broot=equip%2c16%3bmode=flat 

Netgear firmware v3.24 and later supports the 3Com Dual Link (on Netgear router models RT311, RT314, RP114, RO318). I've used both Netgear v3.24 and ZyXEL v3.21 firmware on my RT314. IMPORTANT NOTE: ZyXEL v3.21 firmware only works with certain Netgear routers. Go to this page for details.

SMC. I've tested firmware v1.92 on an 8 port Barricade, and it works with Dual Link. However, two SMC owners report that v1.92 has a minor bug that causes router to drop the Internet connection (issue is NOT related to Dual Link). Both owners have reported the bug (PPP keepalive) to SMC tech support. As a workaround, one SMC owner is using Norton Internet Speed Test - it pings an Internet IP address every 10 seconds and therefore keeps the ISP from dropping the connection.

ZyXEL routers can use v3.21 or later firmware by following the information on this page. This applies to ZyXEL router models P310, P314, and ZyWALL-10.

IMPORTANT NOTE

MOST ISPs ARE USING PPPoE (PPP over Ethernet). If your connection uses PPPoE then you are probably OK (based on my technical review of modem).

THE INFORMATION ON THIS WEB PAGE ONLY APPLIES IF:

a) You originally configured the 3Com Dual Link in "PPP over ATM" mode (PPPoA), AND

b) You are successfully running an Ethernet cable between your PC and the 3Com Dual Link (NOT USB), AND

c) You failed in your attempt to put a router between the PC and 3Com Dual Link

Dual Link's Interoperability With Networking Equipment

The Dual Link supports 3 ADSL transport protocols: Bridged/1483, PPPoE, PPPoA. Let's consider each protocol separately, because PPPoA is a "problem protocol" and is handled differently by various ADSL modem vendors.

PPPoE and Bridged/1483 - NO interoperability issues.  I'm not aware of any interoperability issues with the Dual Link's support of Bridged/1483 and PPPoE. Most ISPs are using PPPoE, so if that is your situation then hooking up the Dual Link to a router via Ethernet should be straightforward. Same should be true for Bridged/1483. The Dual Link appears to support PPPoE exactly as described in the IETF's RFC, but I haven't personally tested it.

PPPoA (PPP over ATM) - Incompatibilities.  The PPPoA (PPP over ATM) mode in the Dual Link has interoperability issues if you want to use a router or a different PPPoE client on your PC. That is the case for modem firmware version 1.0.14.

With the 3Com Dual Link ADSL modem, 3Com has introduced a non-standard PPPoE protocol ("PPPoE:3com"), and it is ONLY used when the modem is configured to run PPPoA to your ISP. 

What impact does that have on you? It means the 3Com modem is incompatible with most home networking equipment that supports the standard PPPoE protocol. That is changing, with the major home router vendors offering support of PPPoE:3com. Most networking equipment (and software) can only speak the standard RFC dialect of the PPPoE protocol. Again, this only applies when your ISP uses PPPoA to establish an ADSL connection to the modem. 

This is all very confusing... because the Internet (WAN) side of the modem uses PPPoA but the PC/router (LAN) side of the modem is running PPPoE. How does that work? The 3Com ADSL modem is operating as a bridge, and it takes care of converting protocols from PPPoA to PPPoE:3com. This is necessary because PPPoA will not run over Ethernet. In fact, PPPoE was developed to handle this very problem.

However, 3Com uses a non-standard protocol for the connection between modem and PC. This non-standard dialect of PPPoE causes all sorts of problems when setting up a home network. For technical details, go to the PPPoE:3com page on this site. Or continue reading this page for solutions and background information.

This "feature" of the 3Com Dual Link has already caused problems with home routers from Netgear, Zyxel, and Linksys. You can check it out for yourself by searching the forums on DSLreports using the string "3com Dual Link" or "PPPoA."

It doesn't have to be this way. Alcatel introduced one of the first PPPoA modems in the market (Speed Touch Home). At the time PPPoE wasn't available, so they wisely used a standard protocol (PPTP) on the PC/router/LAN side of the modem. In fact the Netgear and many other routers support the Alcatel modem because it uses STANDARD PROTOCOLS!

PPPoA modems from vendors such as Cisco and PairGain take another approach. They terminate the PPP session, and connect to the PC via standard Ethernet (just like that router you want to install). No compatibility issues with these modems.

Solutions

Without a router firmware upgrade, you won't be able to use these routers to protect and share your home network. But there is good news! Solutions are available for gateway routers from Netgear, Zyxel, Linksys and SMC as of April 25, 2001. And your in luck with Linux too.

Solution for Netgear and Zyxel Routers

I have loaded and tested Netgear's v3.24 firmware that supports PPPoE:3com.

I originally loaded and tested firmware from Zyxel that fixes the problem. So if you have a Netgear 311/314 (bootbase 1.x only) or Zyxel 310/314 router, there is a solution!

Click here for my instructions for upgrading firmware and configuring a Netgear/Zyxel router.

05/04/2001 - I've finally tested the Netgear v3.24 firmware. No problems.

03/28/2001 - I've been using the Zyxel v3.21 (CA.1) firmware for almost two months. It works great. However, if you have Netgear with v2.x bootbase, you cannot use Zyxel firmware.

Here is what my home network looks like now:

Solution for Linksys Routers

On April 2, 2001, Linksys issued beta firmware 1.38.4c that supports 3Com's problem. I received this email message from a Linksys and Dual Link owner: "Just a quick update to your notes on the 3Com/Linksys problems. I flashed the 1.38.4C upgrade that Simon posted at DSLReports and am finally connected with subject modem and the BEFSR41.  I left the modem configured with the 3Com settings for PPPoA ..."

01/31/2001 - A firmware upgrade request has been issued by a Linksys owner, using information on this website. No estimated timeframe for Linksys to fix the compatibility issue.

Solution for SMC Barricade Routers

SMC firmware v1.92 (April 2001) is compatible with the 3Com Dual Link. I personally verified this with an 8 port SMC Barricade router (borrowed from a friend). I received an email on 4/25/01 from a SMC Wireless Barricade owner that is also successfully using firmware v1.92.

Solution for Linux Routers

I installed Linux on my notebook (dual boot with Win98). Roaring Penguin's rp-pppoe works great. Simple configuration instructions are given later on this page.

No Firmware Support?

Without a firmware upgrade from your equipment vendor, you'll need to connect your PC directly to the modem. So make sure you have a software firewall. ZoneLabs offers a free and powerful software firewall for individuals, the highly rated ZoneAlarm. 

Your First Working Internet Connection

At this point let me digress and provide some background information. Let's start by examining your working Internet connection.

The 3Com CD-ROM installed the "Dialer" application, which is really NTS' EnterNet300 PPPoE client software. EnterNet300 is configured (in the enternet.ini file) to understand 3Com's non-standard dialect (PPPoE:3com). Dialer manages the DSL connection to your ISP, and configures the networking on your PC.

So here is your setup in pictures:

How do I know all this? I spent the better part of November 2000 debugging this problem. I read books and RFCs, played with PPPoE client software, and used  a packet analyzer/sniffer to figure this out. 

DSL Protocols 101

Your Modem to ISP connection requires PPPoATM (PPPoA), so you need to configure the 3Com modem to PPPoA. Don't change it, or you Internet connection will stop working.

There are three incompatible protocols used by DSL providers and ISPs. The situation is similar to digital cell phones, for example you can't use a Qualcomm CDMA digital cell phone on an AT&T digital network. However, most digital cell phones will work in a "fallback" mode with the (first generation) analog network. This is not true for ADSL, so make sure you use the correct transport protocol.

DSL Transport Protocols

• Bridged/1483 was popular when DSL first appeared on the scene.
  
• PPPoA (PPP over ATM) provides routing and transport of PPP sessions over the existing ATM infrastructure. Since dial-up modems use PPP, it is compatible with the billing and authentication systems already in place. But, it doesn't work over Ethernet inside your house. You could buy an ATM network interface card (NIC), but Ethernet is so well established that most ADSL PPPoA modems use either Ethernet or USB. But as discussed earlier, PPPoA won't work over Ethernet. And there are few or no USB routers. Most modems translate or terminate PPPoA into a standard protocol that works with other Ethernet equipment in your house. The 3Com Dual Link translates PPPoA into a non-standard protocol for networking in your house.
  
• PPPoE (PPP over Ethernet) provides same billing/authentication features as PPPoA, but it is designed to work over standard Ethernet. It is now the most popular transport protocol, with all the major players rolling it out. There are few problems with connecting PPPoE modems to other equipment using Ethernet wiring.

The 3Com Dual Link supports all three, so at least if you move or switch DSL providers you won't need to buy another modem.

By the way, this is how 3Com claims PPPoE compatibility on the Dual Link datasheet -- they support Bridged, PPPoA, and PPPoE on the ISP/WAN side of the modem (but not the PC side of the modem). On the PC side of the modem they only claim compatibility with standards for Ethernet, USB and 802.1d Bridging Spanning Tree.

PPPoE Client Software on Computer

So your ISP requires PPPoA, but your PC's Dialer software is running PPPoE:3com to talk with the 3Com Dual Link. How does that work?

At first glance this is all very confusing. The 3Com ADSL modem is operating as a bridge, and it takes care of converting protocols from PPPoA to PPPoE:3com. This is necessary because PPPoA will not run over Ethernet. In fact, PPPoE was invented to handle this very problem. However, 3Com uses a non-standard dialect of PPPoE (PPPoE:3com).

Your "Dialer" (EnterNet300) software on the PC speaks both PPPoE and PPPoE:3com. The Dialer application manages the DSL connection with your ISP, and configures your PC's networking. This software is actually from a company named NTS (recently acquired by Efficient Networks). The Dialer application is part of the EnterNet300 software package. As far as I know, the only other PPPoE client software that can speak PPPoE:3com dialect is RASPPPOE (Windows 98/98SE/ME/2000) and Roaring Penguin's rp-pppoe (Linux users only).

PPPoE and PPPoE:3com always require special software to be installed on your computer, except if your DSL connection is managed by a router. So after the router is installed and working, don't use the PPPoE software on the PC! 

Sharing/Protecting Your Internet Connection

First, you will need a gateway. There are two types of gateways, hardware (e.g. routers from Linksys, Netgear, ...) and software (e.g. Microsoft ICS, Sygate, ...).

To simplify my life, I spent $150 and went with the hardware router/gateway/firewell approach. This allows me to network my home computers, save electricity, use a firewall to protect my computers from hackers due to the "always on" DSL connection, and simplify configuring computers to connect to the Internet (no special software required).

But that also requires a workaround on the router for the non-standard PPPoE:3com protocol.

But 3Com Says Only 1 PC With PPPoA

3Com documentation and tech support will tell you that "PPP over ATM allows only one user at a time per virtual circuit." While true, the statement is misleading.

Using a gateway before the modem will consolidate all Internet traffic to the modem, and you will still only be using 1 ATM virtual circuit. 

So the real answer is ... Yes, you can share your Internet connection with the 3Com Dual Link when operating in PPPoA mode.

Overcoming 3Com's Non-Standard PPPoE Protocol

Let's get back to overcoming the incompatibility between modem and router.

My first instinct was to get 3Com to fix compatibility problem. I tried to resolve the issue with 3Com support, but they literally hung up the phone after telling me "we don't support that, and I won't submit  a firmware upgrade request to engineering." I've filed a 2 bug reports with 3Com's web site, but no response so far other than the auto reply email with a case number. You can check out the ftp link ftp.3com.com/pub/xdsl/hcdl and look in the binaries directory to see if 3Com has issued a firmware upgrade to fix this problem.

UPDATE: 02/05/2001 - 3Com support finally replies to my web-based request by sending an email that answers a question I didn't ask - and the answer was not correct!

Here are five options to overcoming PPPoE:3com:

1. Hardware Router - Upgrade router firmware to a version that supports PPPoE:3com (described earlier on this page). Go to this page for instructions on how I configured my Netgear router with Zyxel firmware. 

2. Hardware Router - Request a firmware upgrade from your equipment vendor. You can send them my Technical Backgrounder (PPPoE:3com). I bought a Netgear RT314 router/firewall to protect/share my DSL connection. I submitted bug reports to Netgear and Zyxel (maker of the electronics). Zyxel was very responsive and sent me beta firmware that fixes the problem! Linksys and SMC have also responded to customer requests.

3. Software Router - If you're running Linux, get the PPPoE client from Roaring Penguin. There is an option in the /etc/ppp/pppoe.conf configuration file to specifically resolve this issue with 3Com Dual Link. I got this working before Zyxel sent me the firmware upgrade. This wasn't a long-term solution for me because I only occasionally run Linux, and didn't want to dedicate a PC to running Linux in order to share connect. But this can work well for the technically inclined if you have a hub and an old PC gathering dust.

4. Software PPPoE Client - If you're running Windows checkout the latest RASPPPOE client. Haven't had a chance to test this yet, but I just received a beta version of RASPPPOE from the author (Robert Schlabbach). I just need to download standard 0.95B release and replace a single .sys file. I'll test soon and report the results. 

5. Software Router - Haven't tested this, but software sharing using MS Internet Connection Sharing (ICS) may resolve the problem. You need to connect your PC directly to the 3Com modem, and use the EnterNet PPPoE client software. Then you must configure the router to work as a hub only. You'll either need 2 Ethernet cards (one for modem, one for network), or connect PC and modem via 3Com's USB port. The EnterNet300 FAQs claim that they support ICS, so this should work. You may need to buy the latest EnterNet300 client software from their web site: http://www.efficient.com/products/enternet.html 

Secure the Netgear/Zyxel Router

At this point my home network is up and running. Now it is time to make sure it is secure.

Netgear and Zyxel routers have an outstanding resource of technical information. The Netgear/Zyxel Forum on DSLReports has excellent information on securing these routers using the integrated packet filtering capabilities. Check out these two links in particular:

Stealth Filters:

http://www.dslreports.com/forum/remark%2C513404%3Broot=equip%2C9%3Bmode=flat 

Guidelines for Securing Your Router:

http://www.dslreports.com/forum/remark%2C595619%3Broot=equip%2C9%3Bmode=flat 

Secure the 3Com Dual Link Modem

Below is a link for the users manual of a related 3Com product. It describes most of the command line interface available if you connect your PC to the Dual Link via the serial port (and use HyperTerminal on the PC). Because they aren't the same product, you'll find a couple of commands missing and a couple of commands described but not available. But it will definitely provide you with lots of useful info on managing the modem:

http://consumer.3com.com/dsl/ethernet/manual/index.cfm 

To secure the Dual Link I have disabled several internal management features. Go to this page for more information:

http://www.bbarrera.com/3com-dual-link.htm 

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