Messing with my DSL router

March 7th, 2006

Recently I am trying to exploit my ADSL connection. The point is that my ADSL router ( a variation of the Comtrend CT-462 producted especially for Chung-Hwa ) – or more specifically , my ISP, – enforces a speed limit if 1Mbps/64Kbps per one PPPoE connection.

However, I can connect my server and my laptop at the same time and still enjoy full speed in both devices (tried measuring it with an apt-get to a nearby university, and some speedtests from the internet). This proves the speed limit is enforced per PPPoE connection. So , the idea is to connect the server and the router through two RS-45 cables, establish two PPPoE connections and split the services between the connections.

But first, some facts:

1) the router’s name, as it is written on the case, is “CT-462C ADSL router”. It has 4 RS-45 ports, a serial port, and a RS-11 port to connect it to the phone jack.

2) Comtrend’s website lists a product by the name of ‘CT-462’, but this one has an additional USB port. Besides, there’s an extra ‘C’ in the name of my router. Thus, I suspect it is a version specially modified for CHT.

3) The router is running in ‘Bridged PPPoE’ mode ( I cannot see the router in traceroutes ) so at the moment it is really a bridge.

4) I connected to it via the serial port, rebooted the router and saw the following

ADSL Router Bootloader
Version 0.8.0 (1.5P)
AD6680 application (CHT20040714) (Build #0)…Looks Ok

Preparing AD6680 application (CHT20040714) (Build #0)……………
Starting System…

All LED Testing…Reset 8995M…..

AD6680 Gateway Software
Version 20040714
Install Exception Hook Function!!
SPI is initiated…..
Reset 8995M…..
Detection VLAN switch
Init KS8995 PORT……………..
DEBUG Tools Installing…

Interface:eth0 IPaddress: Netmask:

Interface:atm0 IPaddress: Netmask:

Interface:lo0 IPaddress: Netmask:
Bridge Group> eth0 atm7

User name:


The problem is that whatever I try to enter enter ‘User name:’ I fail to log on.
Looks like I won’t be able to break in the router short of flashing its firmware, which I don’t want to do since it is my company who pays for the connection.

Other option, i.e. using the ‘bonding’ driver to connect two cables and bond the interfaces into one virtual one is pretty much out, too, since it will not achieve highier thoughput ( it operates in OSI layer 2 by sending ARP packets that MAC address has changed, and therefore maintains just one PPPoE connection over two cables ). This would add redundancy for the cables and network cards in the comp, but that’s not enough to justify complicating the setup so much.

Another try would be to connect the two cables and establish two PPPoE connections, while not bonding the interfaces together. This requires some routing tricks to get right. So, I’ll have to carefully read the ‘Advanced Routing HOWTO’ :

Advanced Routing HOWTO

and figure out a way around this. Chapter 4 seems to have some advice on how to establish multiple routing tables. ( for sure I’ll need to recompile the kernel and add support for ‘advanced router’ and ‘routing policy’

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