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Routing works to other intreface, but nowhere beyond it...

Posted on 1997-04-18
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Last Modified: 2010-03-18
I have a router that was working just fine between 2 class C
networks (both with default netmask).  Now I've moved it so
one of the interfaces is on a class B network (with netmask
of 255.255.255.252).  The class B network belongs to my ISP,
the class C is my own.  So here is the problem:

I can telnet to my router on its external interface just fine.  I can then telnet to the internal machine.  From the
internal machine, I can telnet to either of the router's
interfaces.  From the internal machine though I cannot telnet to any address beyond the router's external interface (including the router's default gateway, even though I *CAN* telnet to the router's default gateway from the router).

Here's the setup (the class B network number is different, but everything else is correct):

Router has interfaces setup as:
ADDRESS = 163.185.46.42
NETMASK = 255.255.255.252
NETWORK = 163.185.46.40
BROADCAST = 163.185.46.43

&&

ADDRESS = 204.74.32.2
NETMASK = 255.255.255.0
NETWORK = 204.74.32.0
BROADCAST = 204.74.32.255

---[ netstat -r on this machine shows ]---
localhost       *               255.255.255.255 UH     3584 0          0 lo
163.185.46.40    *               255.255.255.252 U      1500 0          0 eth0
204.74.32.0     *               255.255.255.0   U      1500 0          0 eth1
127.0.0.0       -               255.0.0.0       !         - -          - -
default         rmi             0.0.0.0         UG     1500 0          0 eth0

---
The "internal" machine is setup as:
ADDRESS = 204.74.32.3
NETMASK = 255.255.255.0
NETWORK = 204.74.32.0
BROADCAST = 204.74.32.255

---[ netstat -r on this machine shows ]---
204.74.32.0     *               255.255.255.0   U      1500 0          0 eth0
127.0.0.0       *               255.0.0.0       U      3584 0          0 lo
default         204.74.32.2 0.0.0.0         UG     1500 0          0 eth0

---

I guess the real reason I'm confused is that if I'm able to contact the router's external interface from the internal machine -- shouldn't I be able to contact *any* other machine?
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Question by:michaelbentley
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3 Comments
 
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Expert Comment

by:grovedc
ID: 1584410
you are obviously trying to route from one network to another.  what does netstat -r show on both machines?
if the router is a linux box was the kernel compiled with ip forwarding turned on?
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Author Comment

by:michaelbentley
ID: 1584411
Edited text of question
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Accepted Solution

by:
ruski earned 100 total points
ID: 1584412
not nessessarily judging by your netmaks. It is setup only for your own class nework and what you might need is either a gateway setting or a different netmask.  try either one of the following:
   ifconfig eth0 netmask 255.255.0.0
or
   route add default gw your_IP_address netmask your_netmask

seva
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