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DSL, firewall and routing

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Routing is one of the topics I don't seem to understand. I have a computer action as firewall for a lan with two ethernet cards. Connection to the internet was done through a hardware router. I now want to get rid of the hardwarerouter as it is not configurable. I ran pppoeconf to connect to the internet via the dsl modem. pppstatus tells me that the connection is up but I don't get a connection anywhere. Neither ping with ip address nor with host name works. I think this has to do with routing and gateway. As gateway, the ip address of the hardware router was used. Changing this to the local ip address of eth0 (card formerly connecting to the hardware router) did not help. Now what can I do?
1. In the firewall as well as in the routing table, eth0 is used as one of the devices. Do I have to exchange this for ppp0?
2. Where can I look for misconfiguration?
Thanks for your help.

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if you use pppoeconf...

Submitted by pinniped on Mon, 2006-10-16 16:06.

Then everything else should automatically be set up for you (gateway etc etc). The first thing of course is to make sure that PPPoE is the correct protocol to use. Many modern modems handle everything and just provide you with a dhcp server so all you have to do is plug in your computer once the modem has been configured.

If you do need PPPoE then I suspect you may have any of:

1. 'eth0' is incorrectly configured via /etc/network/interfaces
solution: make sure the entry is like this:
auto eth0
iface eth0 inet manual

2. You made a mistake while running 'pppoeconf' - check the configuration files which were generated and also check the authentication files. Your config file should have lines like:
noauth
replaceroute
replacedefaultroute
usepeerdns
'noauth' means your ISP will not be challenged to prove its identity; this is the 'normal' operation of most ISPs
'replaceroute' will use routing information provided in your ppp negotiations
'replacedefaultroute' will replace your default gateway (which is probably undefined before the first time you run 'pon')
'usepeerdns' will request 2 DNS addresses during the ppp negotiations; this is important if you want to be able to resolve names (and everyone wants that).

The config files will be:
/etc/ppp/options (for default options, but these can be overridden by the next config file)
/etc/ppp/peers/yourISPconfigFile - contains config info for a particular ISP connection. Of course the names that exist depend on how you answered pppoeconf
/etc/ppp/pap-secrets : login data if you use 'pap' authentication
/etc/ppp/chap-secrets : login data if you use 'chap auth

Do NOT bring up any firewalls until you know that your internet connection is working correctly, otherwise we will waste a lot of time trying to track the wrong problem. When everything is correctly configured, the WAN side of your firewall will be 'ppp0', NOT 'eth0' since the outgoing connection is PPPoE.

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