DSL, PPPoe, EoA, MTU, WTFBBQ!

Router/Modem

I like when simply reconfiguring stuff that I already have makes it work better. My internet connection was having issues when I was using hundreds of simultaneous connections, with new connections being hard to open. It wasn’t a bandwidth issue, as I wouldn’t be using all of my 7 down/1 up connection, and could max it out on 1 connection just fine. Now, I have no problems related to number of connections. (Maybe I could try to do a 1000 connections and then see if spawning connections works)

To resolve the issue, I had my router, a Buffalo WHR-G54S running Tomato do the PPPoE connection instead of on my TrendNet TDM-C400 DSL modem.

Shortly put, I bridged the DSL and ethernet connections on my DSL modem, and then had my router do the PPPoE connection.

The configuration on the modem is going to be modem specific, and in my case was to make a EoA(Ethernet over ATM) connection above the DSL link, and then bridge the EoA interface with the Ethernet interface.
Then I added the PPPoE connection in the router, so that the DSL modem was only seeing a single connection. This is different from having the router be in the DMZ of the Modem, because the modem isn’t handling any connections, and isn’t doing any NAT either. The router has to manage connections/NAT anyways, so might as well have it do the PPPoE also.

Due to the 8-byte overhead in PPPoE, the recommended MTU is 1492, 8 down from the 1500 MTU in raw Ethernet.

One issue now is that I can’t access the administration page of my modem, since the WAN port of the router is doing PPPoE for everything. One way to fix this is to have a switch between the WAN port of the router, a LAN port of the router, and the Ethernet port of the modem. Since the only way to get a packet over the DSL connection is through the PPPoE, the switch between the WAN and LAN ports on the Router isn’t a huge security risk.
(Actually, plugging the WAN into a LAN port on the router, and then plugging the modem into a LAN port might work. That is just awesome! Maybe some routers support doing PPPoE and local network access over the WAN port…?)

In this configuration, with 280 connections doing 500KBps down/50 KBps up, no issues creating connections, but my laptop is starting to have serious lag issues. Which is one reason why I ordered a new computer to replace this single core laptop. The cpu usage on my router did spike to .4 with 50 connections being opened out of 200, but no issues there.

2 thoughts on “DSL, PPPoe, EoA, MTU, WTFBBQ!

  1. wow, google-fu is funny…

    So I was helping a friend with the same dsl modem problem and was dying looking for info like this. Well I had finally found the manual and almost figured it out, so I searched “eoa mtu” and you were like the first result. With the exact modem. *laughs*

    Thanks for sharing your experience, the network here is much happier as well now that I have something else doing PPP. 😀

    • Re: wow, google-fu is funny…

      Yeah, it seems like this modem doesn’t have enough RAM to handle hundreds of connections, but has the power to handle a lot of bandwidth.

      I put lots of terms that people might search for so that it could be found easier. Seems like that worked, and I am glad that it helped someone.

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