Re: signle network interface with 2 IPs on different subnets

From: Darren Dunham (ddunham_at_redwood.taos.com)
Date: 05/27/03 

Date: Tue, 27 May 2003 15:36:10 GMT

Simon Lee <Simon.Lee@asia.ing.com> wrote:
> Routing Table: IPv4
> Destination Gateway Flags Ref Use Interface
> -------------------- -------------------- ----- ----- ------ ---------
> 10.1.2.0 10.1.2.202 U 1 48 qfe0
> 224.0.0.0 10.1.2.202 U 1 0 qfe0
> default 10.1.2.1 UG 1 132
> 127.0.0.1 127.0.0.1 UH 2 10 lo0
> host3# ping 10.1.3.1
> 10.1.3.1 is alive

Note that based on your routing table, 10.1.3.1 is not local to any
interface. Therefore it attempts to reach it by using the gateway at
10.1.2.1.

> host3# /usr/sbin/ifconfig qfe0:1 plumb
> host3# /usr/sbin/ifconfig qfe0:1 10.1.3.202 netmask 255.255.255.0
> broadcast 10.1.3.255
> host3# /usr/sbin/ifconfig qfe0:1 up

Now you've set up a route for 10.1.3.0 as local to the machine

> host3# route add -net 10.1.3.0 10.1.3.1

Whoa, whoa, whoa... wrong.

The net 10.1.3.0 is *local* to your interface after you brought it up.
The command you've typed makes no sense. You're saying that you get to
that network via a host on that network. Impossible.

Why that command? It should already be in the route table after the
interface was brought up.

> Routing Table: IPv4
> Destination Gateway Flags Ref Use Interface
> -------------------- -------------------- ----- ----- ------ ---------
> 10.1.2.0 10.1.2.202 U 1 49 qfe0
> 10.1.3.0 10.1.3.202 U 1 7 qfe0:1
> 10.1.3.0 10.1.3.1 UG 1 0

By typing that route command, you have two routes to 10.1.3.0. The
second line is completely bogus.

The first line may or may not be correct, based on your router
configuration. 

-- 
Darren Dunham                                           ddunham@taos.com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >