Access to sub network unreachable.

[Rick Stevens]

Robin Laing wrote:
> Simon Slater wrote:
>>     Hi all,
>>         I'm sure I have missed something simple (or done something 
>> stupid) but
>> have no idea what so I'll ask anyhow.
>>
>>     All the computers on our SOHO network had static addresses in the
>> 192.168.0.1-9 range with netmask of 255.255.255.0 and all worked fine
>> for ages.  Now I have a Linksys gateway which has a default address of
>> 192.168.1.1 for configuration.  It works fine as a DSL router but I
>> cannot use a browser to access the configuration.  All I get is "An
>> error occurred while loading http://192.168.1.1: Could not connect to
>> host."  Pinging returns "Destination Host Unreachable".
>>
>>     I changed the netmask for the ethx device to 255.255.0.0 but this 
>> made
>> no difference.  What have I forgotten?

Odds are that the router also has a netmask of 255.255.255.0 (or a /24).
If that's the case, then it can't talk to your client since your client 
isn't on the router's LAN as far as the router is concerned.  Your
client can talk to the router with a /16, but the router can't reply to
you as it'd try to talk to you over its WAN port.  Options:

1. Change all of your client machines to 192.168.1.xxx with netmasks of
255.255.255.0 (/24) to conform to the router's defaults, or

2. Change the netmask on the router to 255.255.0.0 (/16) and all of the
client machines to the same, or

3. Change the IP and netmask of the router to 192.168.0.xxx/24 and leave
your clients alone.

I'd vote for number 3...it makes your new router look like the old 
router.  Remember, though, that if you ever reset your router to the
factory defaults, you'll need to change its IP again afterward or
you'll be right back here where you started.  :-)

How to change it?  On your client:

1. # ifconfig eth0 192.168.1.whatever netmask 255.255.255.0
2. (browse to 192.168.1.1 and change the IP on the router)
3. # ifconfig eth0 192.168.0.whatever netmask 255.255.255.0 (needed
because your router is now on 192.168.0.0/24)


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- Rick Stevens, Systems Engineer                      ricks at nerd.com -
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