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

Posted on 1997-04-18
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  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:



---[ netstat -r on this machine shows ]---
localhost       *      UH     3584 0          0 lo    *      U      1500 0          0 eth0     *        U      1500 0          0 eth1       -            !         - -          - -
default         rmi            UG     1500 0          0 eth0

The "internal" machine is setup as:

---[ netstat -r on this machine shows ]---     *        U      1500 0          0 eth0       *            U      3584 0          0 lo
default         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?
Question by:michaelbentley

Expert Comment

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?

Author Comment

ID: 1584411
Edited text of question

Accepted Solution

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
   route add default gw your_IP_address netmask your_netmask


Featured Post

New! My Passport Wireless Pro Wi-Fi Mobile Storage

Portable wireless storage to offload, edit, and stream anywhere.

High-capacity, wireless mobile storage designed to accompany professional photographers and videographers in the field to easily offload, edit and stream captured photos and high-definition videos.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I have seen several blogs and forum entries elsewhere state that because NTFS volumes do not support linux ownership or permissions, they cannot be used for anonymous ftp upload through the vsftpd program.   IT can be done and here's how to get i…
Note: for this to work properly you need to use a Cross-Over network cable. 1. Connect both servers S1 and S2 on the second network slots respectively. Note that you can use the 1st slots but usually these would be occupied by the Service Provide…
This demo shows you how to set up the containerized NetScaler CPX with NetScaler Management and Analytics System in a non-routable Mesos/Marathon environment for use with Micro-Services applications.
This video demonstrates how to create an example email signature rule for a department in a company using CodeTwo Exchange Rules. The signature will be inserted beneath users' latest emails in conversations and will be displayed in users' Sent Items…

914 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now