Half-bridge mode and PPPoE

Discussion in 'Other Linksys Equipment' started by moshi16, May 18, 2007.

  1. moshi16

    moshi16 LI Guru Member

    :confused: what's the difference between half bridge mode and pppoe?

    Based from what I have learned from other forum threads, you set the modem in half-bridge mode so that the modem will handle the pppoe authentication to the ISP rather than the bridged mode where it only passes information to the pc and you will need win xp's built-in pppoe client or other PPPoE clients for the authentication.. Now my question is, what's the difference of PPPoE with Half bridge mode? Isn't setting the modem to PPPoE the same as setting it to half-bridge? ​

    my setup is like this: AM300-->WRT54G--PCs

    Thanks! for your feedback in advance. :confused:
  2. ifican

    ifican Network Guru Member

    Setting it to just pppoe will make the modem act also like a router and most likely do nat. Will this work, yes, it just becomes a headache when you try and port forward anything. If you are not port forwarding you can set it either way without any issue. Half bridge mode does exactly as you said, the modem handles the pppoe connection and bridges the rest of the traffic across to you internal router which will handle your nat connection.
  3. moshi16

    moshi16 LI Guru Member

    wow :grin: thanks ifican!
  4. mstombs

    mstombs Network Guru Member

    If you have pppoe then full bridge makes the modem 'transparent' - sometimes too transparent making it difficult to get to the modem web pages (but there are fixes for this). So if you can you should!

    Half Bridge is necessary for those of us whose ISP do not support PPPOE. With PPPOA the modem has to act as a router, half-bridge mode should turn off NAT and pass the external ISP given IP address to your PC/router. If you don't have half-bridge then you usually have to get the modem to run NAT and use the dmz which generally causes other problems.

    A possible advantage of half-bridge PPPOE is that the modem will handle the Username:password and no need to run a PPPOE client on your PC/router.

    The term zipb (zero installation ...) is sometimes used for half bridge - this could be used by ISPs to send out modems pre-configured with username/password, which will work with any home setup with Ethernet ports set to 'automatic'.
  5. moshi16

    moshi16 LI Guru Member

    am300 half-bridge

    Ive been trying to set up my AM300 in half bridge mode and connected to it is a WRV200. I set the modem to PPPoE half bridge and it gets the IP address from my ISP. Then using my router's WAN port, I connected the modem to it. My router gets the same IP address as what the modem is getting but my subnet mask is and I can't get online. What am I doing wrong? I am using the 1.00.19 fw already :confused:
  6. mstombs

    mstombs Network Guru Member

    I don't know the AM300 nor the WRV200 but this sounds like the same problem I have observed with ADSL2MUE and WRT54GS, which I can properly fix in Hyperwrt Thibor (or cheat in the modem):-


    Can you manually spoof the netmask in the WRV200. If the ISP has only given you one IP address the full netmask is technically correct. If you cheat with a smaller mask you will lose internet access to those addresses now marked as local.
  7. moshi16

    moshi16 LI Guru Member

    My subnet mask from my ISP should be Why is the modem passing the subnet mask info to the router as Is this normal when the modem is set to half-bridge? To narrow down, I connected my computer back to the modem and manually assigned the same IP address I got from the modem but this time with a class c subnet mask and it worked. I need my router for the VPN tunnel that's why I'm doing this. Thanks again!
  8. mstombs

    mstombs Network Guru Member

    Windows XP pro and a recent Linux distro (and Hyperwrt Thibor with the firewall script) cope with the full netmask for me. I doubt if you have been given the whole class c subnet for your own use so to use it is a 'fudge', and this does not work at all if the gateway given by the ISP is not even in the same primary network :- see here for an example


    In your case why don't you use PPPOE full bridge mode?
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