Interesting network problem

[Robert Nichols]

Konstantin Svist wrote:
> David G. Mackay wrote:
>> 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
>>   
> 
> you get to write in any gateway in system-config-network, it's not 
> limited to same subnet.

And you can add explicit routes there, too.  They _do_ get set up
by the networking scripts.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.