PPPoE configuration tip

wseyllerwseyller Member Posts: 44 ■■■□□□□□□□
Thought I would share my experience this in case anyone else ran into this.

I was doing a PPPoE configuration lab.

I was first using GNS3 with two routers. I connected a cable between them initially on the fast ethernet ports before I did the configuration.

After doing the configuration the pppoe session would not show in the UP state. I did not receive an ip address on the client side.

I have some real equipment so I decided to do the configuration on two Cisco 1841 routers. The patch cable I had between the fast ethernet ports was a straight through type which normally works fine using auto-mdix.

After configuration it still didn't work for me and I noticed the line protocol was down and there were no lights on the ports. So I decided to make a crossover cable which did the trick.

I went back to my GNS3 config and what I had to do was delete the cable and re-add it. I'm guessing when I first added a cable it auto detected to use a straight through cable???

It seems PPPoE configuration on the real equipment requires a crossover cable even with newer equipment that has auto-mdix.

And in GNS3 possibly when you delete and re-add the cable it then detects that you need a crossover cable because of the PPPoE configuration???


  • alfred06alfred06 Member Posts: 96 ■■□□□□□□□□
    strange. never had this issue with GNS3. I always do the cables first as well before turning them on and doing the configuration. never really paid attention to straight-cross over on GNS3 lab it always just work. is it just on the PPPoE configuration or on all the labs you do?
  • WastedHatWastedHat Member Posts: 132 ■■■□□□□□□□
    wseyller wrote: »
    It seems PPPoE configuration on the real equipment requires a crossover cable even with newer equipment that has auto-mdix.

    Are you referring to GNS or physical here? I came accross this same problem when I was studying, I was certian my 1841's had auto-mdix from previous lab work and spent a while trying to pin point the issue. Eventually I made a cross-over cable and it worked.

    While I was searching I seen mixed feedback but the consensus of my results seemed to say that 1841's did not have auto-mdix.

    After the cable issue did your labs work as expected? I had a lot of temperaments with my PPPoE labs, sometimes they worked and sometimes they didn't with the exact same commands, done them over and over trying to figure out why. I think it had something to do with trying to configure CHAP authentication on an up/up interface but I'm still not entirely sure.
  • wseyllerwseyller Member Posts: 44 ■■■□□□□□□□
    Once I made the crossover cables it works fine. It is only the PPPoE that barks about the cable.

    I then found in one of my study books that it explicitly mentions to make sure you use a crossover cable for the PPPoE lab.
  • ebohlmanebohlman Member Posts: 26 ■■■□□□□□□□
    What likely happened here is that you were connecting a a desktop or laptop to your 1841. Auto-MDIX only requires one side of the connection to support it, and most desktop/laptop network interfaces built in the last 12 or so years do.

    AFAIK, 1841 FE ports don't support it, so you'll need crossover cables if you're connecting them together.
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