Interesting network problem
David G. Mackay
mackay_d at bellsouth.net
Fri Aug 17 01:03:48 UTC 2007
On Thu, 2007-08-16 at 14:46 -0700, Konstantin Svist wrote:
> David G. Mackay wrote:
> > I have a netopia 2241N dsl modem provided by my ISP (AT&T), which I
> > access through an ethernet port. The unit can be configured in pass
> > through mode so that the public internet address is bridged, i.e. my
> > ethernet card is assigned the public address. This has been working
> > well for some time now.
> >
> > There was a network outage the other day, and when service was restored,
> > the gateway on the remote side had changed. The fun part is that the
> > gateway is on a different class A ip net than my public ip. I can
> > resolve all that by doing:
> > route add -net e.f.g.h netmask 255.0.0.0 dev ethx
> > route add default gw e.f.g.h
> > where e.f.g.h is the external gateway ip.
> > This borks up the /etc/sysconfig/network-scripts/ifcfg-ethx scripting.
> >
> > Is there a better way to handle this, other than kludging things in
> > rc.local?
> >
> Normally, DHCP takes care of these little problems.. but if you're not
> using it (and using static IP config instead), just use the GUI utility
> system-config-network - it
> should set all these values correctly
It is a static address, so DHCP is not appropriate. And, I suppose,
system-config-network would accept the gateway and ip addresses. The
problem is that the gateway is on a different subnet than the ip by most
normal networking rules. The modem doesn't show the netmask, so I
suppose that AT&T might have CIDRed a couple of class A addresses
together. But, without that, the gateway will be unreachable until you
add the route add -net, which doesn't normally occur in the network init
scripts.
Dave
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