Re: Cant get internet access on my router (sent again)

[Ray Olszewski <ray@comarre.com>]

At 08:59 PM 10/21/2004 +0200, Ole Martin Handeland wrote:

>sending this again, since im still having problems...

I'm sorry, but to get real help, you need to answer ALL of the questions, 
not just some of them.

The list below of INPUT chain rules has entries ONLY for an eth1 interface, 
which you have not previously mentioned (but which I will guess is your LAN 
interface). For that reason, it wil DROP all packets intended for a ppp0 
interface. (Notice that its final rule, a DROP rule, has matched a lot of 
packets.)

Since you have no entries in the OUTPUT chain and (you previously said) its 
default policy is DROP, no traffic will go out on ANY interface.

And if you have no entries in the FORWARD chain and its policy too is DROP 
... well, you get the idea.

OK, this time around we need to know --

         1. How do you update your firewall ruleset when the PPPoE (ppp0) 
interface is set up (or when it gets a new address)? The PPPoE daemon 
probably calls a script for this, but you need to tell us the details, so 
we can figure out why it (apparently) isn't working.

         2. Am I correct in assuming that you are NATing the LAN? If so, 
the nat table (probably its POSTROUTING chain) is doing the SNAT or MASQ 
needed. What does
         iptables -nvL -t nat
report about this? (This is probably OK, if your prior report that setting 
the default-table policies to ACCEPT makes "everything" work.)

         3. More generally, what script is setting these rules up in the 
firat place? Are you using some routing capability that comes as part of 
FC2? Or are you using a drop-in firewall/router package of some sort (like 
Shorewall -- though it is plain from the ruleset that you are not using 
Shorewall, so I mention it only as an example)? Or did you craft something 
yourself?

         4. What actual failures are you encountering? "im still having 
problems" is on the vague end of descriptions.

         5. How do you *want* this router to operate? Just using default 
ACCEPT policies isn't really very good firewalling ... but in practice, it 
isn't usually all that vulnerable, since most breakins target Windows, not 
Linux, and the NATing makes the Windows machines invisible to connections 
that initiate from outside.




>  well... here comes my "iptables -nvL":
>
>Chain INPUT (policy DROP 980 packets, 127K bytes)
>  pkts bytes target     prot opt in     out     source destination
>  2061  408K ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:10000
>15955 1602K ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
>0.0.0.0/0           tcp dpt:22
>   853  111K ACCEPT     tcp  --  *      *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:80
>   991  150K ACCEPT     udp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           udp dpts:137:138
>  271K   37M ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:139
>     0     0 ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:445
>     0     0 ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:8080
>     0     0 ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           tcp dpt:443
>     0     0 ACCEPT     udp  --  eth1   *       0.0.0.0/0 
> 0.0.0.0/0           udp dpt:443
>67131 3090K ACCEPT     tcp  --  eth1   *       0.0.0.0/0 
>0.0.0.0/0           tcp dpts:5900:5902
>     0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0
>  2416  167K LOG_DROP   all  --  *      *       0.0.0.0/0 0.0.0.0/0
>
>and for my forward and output chains, there is no rules...
>
>thank you so much for your answers!
>
>Ray Olszewski wrote:
>
> > At 12:29 PM 10/17/2004 +0200, Ole Martin Handeland wrote:
> >
> >> Hi,
> >>
> >> I cant seem to get internet access on my gateway machine, using fc2 and
> >> iptables firewall. I have a eth0 connection (and a ppp0 connection using
> >> eth0 to connect to my adsl provider) and a eth1 connection which i use
> >> to connect to my local network (with a dhcp server on this gateway).
> >>
> >> i have gotten this gateway to connect to the net, and the network from
> >> eth1 gets internet access. my problem is that my gateway dont get net
> >> access itself. when i set default action to allow in my iptable,
> >> everything works.
> >> anyone knows which rule(s) i should apply to get internet access working
> >> on this gateway?
> >
> >
> >
> > The core problem you face is that different chains, not just different 
> rules, are involved.
> >
> > When other hosts on your LAN use this gateway to connect to the 
> Internet, the packets are processed by the FORWARD chain in the default 
> table (and by the  PREROUTING and POSTROUTING chains in the nat table).
> >
> > When the host itself tries to connect to the Internet, the packets are 
> processed by the INPUT and OUTPUT chains in the default table.
> >
> > So ... if "everything works" when you set the default action to ACCEPT 
> (there is no action "allow", so I assume you mean ACCEPT), then it 
> probably means you do not have specific ACCEPT rules in suitable places 
> in the INPUT and OUTPUT chains. That's not odd for a router ... mine is 
> set up that way, allowing direct access for only a few things the router 
> absolutely needs, like DNS resolution. But it is inconvenient for a 
> general-purpose host that is also acting as a router.
> >
> > The exact rules you need to add, and where you need to add them, 
> depends on what you do have in the INPUT and OUTPUT chains (which you can 
> check best with "iptables -nvL"). If you want finer control than a 
> genrealized ACCEPT policy, the actual rules need to be tailored to what 
> you want to allow, what to disallow, and you haven't told us your 
> situation in that regard.
> >
> > Describe more what you want to accomplish, and tell us the rules you 
> currently have in the INPUT and OUTPUT chains, and I -- or someone here 
> -- may be able to give you more specific advice that fits your needs. As 
> it is, anything anybody suggests will be guesswork.
> >
> > Oh, one final thing. Since you are using PPPoE for your Internet 
> connection, iptables does need to know to update its ruleset after PPPoE 
> negotiation is complete. It also needs to know that ppp0, not eth0, is 
> your external interface. It probably does all of this, since NATing the 
> LAN works, but it is always *possible* that you have a problem there. 
> Once again, only examination of the rulesets in the relevant 
> tables/chains will tell.



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