Bug 82600 – NAT does not work when following Home Router Guide literally (eth1 / ppp0 confusion)

• Product: [OLD] Docs-user
• Status: RESOLVED INVALID

[Description Pavel Mayer 2005-02-19 10:32:08 UTC]

When setting up a home router following the home router guide, there is a warning in a red box about " From now on, when you see examples that utilize 'eth1', substitute with 'ppp0'."

However, after this warning, there are some examples where you must *not* follow this advice. (Code Listing 3.2: Setting up eth1)

Then possibly days later (after resolving the unstable baselayout problem, see Bug #68887), in Code Listing 5.3: Setting up iptables, 'eth1' indeed must be substituted by 'ppp0'; you will not get any error message, and iptables -t nat -L also will not give you any hints what is wrong, only NAT does not work.

After using:
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
instead of
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

masquerading worked.
Therefore I am not sure what the purpose of 
iptables -A FORWARD -i eth1 -d 192.168.0.0/255.255.0.0 -j ACCEPT
is and whether is should be also
iptables -A FORWARD -i ppp0 -d 192.168.0.0/255.255.0.0 -j ACCEPT

Is there a reason why the example does not use ppp0? It is very tempting to use eth0 and eth1 as written in the example even beeing aware of the warning.

Anyway, finally I got things work nicely thanks to this useful guide.

Reproducible: Always
Steps to Reproduce:
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[Comment 1 SpanKY 2005-02-19 10:43:03 UTC]

Code Listing 3.2 is only for 'Cable and/or dynamic/static IP' users, not DSL

i dont see any other issues that need to be covered in this bug report ...

[Comment 2 Simon Roby 2005-06-01 22:43:59 UTC]

As someone who lost half a day because I didn't notice the stupid little red 
box, I agree. And even afterwards, substituting eth1 with ppp0 was a very 
confusing and frustrating experience since you have to be careful not to 
substitute eth0 too. 
 
For sake of clearer documentation, in sections relating to both adsl and 
dynamic/static setup there should be a dummy term used to replace the 
unappropriate eth1, something like "<wan>" (without the quotes, but with the 
angle braces). Seriously, for everyone on PPPoE this guide is confusing, and I 
bet most people reading it _are_ PPPoE users!!