Re: strange network problems

[Tony Nugent <tony linuxworks com au>]

On Tue Oct 29 2002 at 23:16, "Avery Pierce" wrote:

> Im using a PII 350 with 2 SMC 1211TX Nics (realtek 8139).  Its
> used for a firewall / NAT Gateway with 1 pc behind it.  If im
> uploading a file on the firewall my pc behind the firewall had no
> internet access on tiemouts.  I get heavy packet loss when I ping
> an outside server..like google.com.  When uploading from my pc
> through the firewall everything works just fine.  Downloading also
> works fine .  Im logging all dropped packets with iptables and
> nothing is behind dropped.  There isnt any errors in
> /var/log/messages pertaining to the network interfaces.  ive tried
> updating anything that might be causing this.

(please wrap your text to make it readable, like I've just done).

> System:
> Redhat 7.2 Enigma
> Kernel 2.4.18-17.x
> Nic Driver 8139too
> iptables 1.2.5-3
> 
> I connect to the internet with a SurfBoard sb4100 cablemodem through Adelphia.
> My pc connects to the firewall using a crossover cable.  My pc has an smc 1211tx nic also.
> Any ideas would be appreciated.  Thanks in advance.
> 
> Heres an ifconfig on the firewall

/sbin/ifconfig is becoming obselete.  Use "/sbin/ip -s link" (and/or
"ip -s a") to get a better output.


> eth0      Link encap:Ethernet  HWaddr 00:E0:29:1D:98:6E
>           inet addr:192.168.200.1  Bcast:192.168.200.255  Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500 Metric:1
>           RX packets:35202 errors:6 dropped:0 overruns:0 frame:0

(I'd check what is causing these errors if they persist).

>           TX packets:24688 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100
>           RX bytes:2402686 (2.2 Mb)  TX bytes:2912915 (2.7 Mb)
>           Interrupt:5 Base address:0xc000
> 
> eth1      Link encap:Ethernet  HWaddr 00:E0:29:95:60:60
>           inet addr:X.X.X.X  Bcast:255.255.255.255  Mask:255.255.255.0

This looks like where your problem is, why does it have a /24 mask
but an all-ones broadcast address?  It should be X.X.X.255 (where
the X's refer to the inet address).

What have you got in /etc/sysconfig/network-scripts/ifcfg-eth1 ?
That interface doesn't seem to be configured right.

If that public interface is configured via dhcp (eg, cable), then
there could be a problem with your ISP's configuration (which would
be unforgivable :-)

>           UP BROADCAST NOTRAILERS RUNNING  MTU:1500  Metric:1
>           RX packets:26893 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:35608 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100
>          RX bytes:3045857 (2.9 Mb)  TX bytes:2968880 (2.8 Mb)
>          Interrupt:10 Base address:0xe000

Yeah, the itself card is working fine.

The problem could be elsewhere (in your routing table, which you can
see with "/sbin/ip route") or in your actual firewall rules (which
you haven't shown here, but not likely to be the cause if some
packets are getting through).

But the bad 255.255.255.255 broadcast address needs to be fixed (if
that is what it really showing up as).

> Avery Pierce
> Camteq Professional Systems
> www.camteq.com

Cheers
Tony