Re: Debugging network problems

[Martijn Lievaart <m@rtij.nl>]

David Leangen wrote:
> Hello!
>
> My network was just changed from a vanilla ADSL connection to direct
> ftth. There is now a network connector with a  100MB/s entry, which gets
> routed to a Buffalo Broad station.
>
> I'm having some troubles and my debugging so far has not been
> successful, so I'm hoping some more experienced hands can give me some
> advice.
>
>
> First of all, my previous setup was working exactly as I wanted.
> Essentially, when making the switch to the new network, on my
> firewall/proxy machine, I just did:
>
>   adsl-stop (to stop the pppoe daemon)
>   ifconfig eth0 new.ip.address up
>   route add default gw ip.address.of.broad.station
>
> Then in my iptables, I changed:
>
>   -A POSTROUTING -o ppp0 -j MASQUERADE
>
> to 
>
>   -A POSTROUTING -o eth0 -j MASQUERADE
>
>
> Here's what's happening now...
>
> Generally, I can connect to the outside world, and the outside world can
> connect to me. By this, I mean that each of the local machines behind my
> proxy can connect.
>
> However, the connections back to my own URL are sporadic. In other
> words, sometimes I can connect, sometimes I can't. Assuming my domain is
> my.company.com, when I try to connect to my.company.com from within my
> network, sometimes I can, sometimes I can't, but I have not at all
> figured out a pattern.
>
> When this happens, domain names are being resolved, but I get
> "Connection timed out" errors.
>
> I guess I first need to check to see if I can't get out, or I can't get
> back in.
>   

Sounds like an PMTUD issue. Do you allow all ESTABLISHED packets in, not 
just tcp?

M4