start up script

start up script

[Ravi Kumar Munnangi]

Users,
 
  Iam working in a LAN with a number of systems.
  A system has X hardware address and another has Y
hardware address.
  I want to set the hardware address of the second
system
  also to X.
  I also want to set the primary IP addresses of both
  systems to 172.31.19.30.
  So when I ping to 172.31.19.30, both the systems
  should respond.

  The topology of LAN we are using is star. All
systems
  are connected to a Switch.
  Does the settings change when we are using a bus
  topology?
  
  Do I have to write a start up script?
  How should I write?
   
  My actual goal is to start 2 web servers on two
  systems with same hardware address and same 
  primary IP address but with different secondary
  IP addresses. So when a request comes from a 
  client, the request has to be seen by both 
  systems. I will write some mechanism by which only
  one will respond finally.

  Please help!
  
  Thanks in advance,
  ravikumar

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Re: start up script

[John Kelly]

Hi,
On Sat, 6 Mar 2004 02:43:03 -0800 (PST)
Ravi Kumar Munnangi <munnangi_ivar@yahoo.com> wrote:

> Users,
>  
>   Iam working in a LAN with a number of systems.
>   A system has X hardware address and another has Y
> hardware address.
>   I want to set the hardware address of the second
> system
>   also to X.
>   I also want to set the primary IP addresses of both
>   systems to 172.31.19.30.
>   So when I ping to 172.31.19.30, both the systems
>   should respond.
> 
>   The topology of LAN we are using is star. All
> systems
>   are connected to a Switch.
>   Does the settings change when we are using a bus
>   topology?

First up I don't think you should be doing this. having two systems with the same 
hardware address on a LAN is going to break things in 'interesting' ways. ARP requests 
are not likely to work as you expect and the switch is likely to get very confused if 
it has the same hardware address answering on two different ports.
But then maybe I am wrong.
For what it is worth, here is an extract from the ifconfig man page:
===================================================================
 
hw class address
       Set  the hardware address of this interface, if the device driver supports this
       operation.  The keyword must be followed by the name of the hardware class  and
       the  printable ASCII equivalent of the hardware address.  Hardware classes cur-
       rently supported include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom
       (AMPR NET/ROM).

====================================================================
So if the hardware supports it, ifconfig can do it.

> My actual goal is to start 2 web servers on two
> systems with same hardware address and same 
> primary IP address but with different secondary
> IP addresses. So when a request comes from a 
> client, the request has to be seen by both 
> systems. I will write some mechanism by which only
> one will respond finally.

To me it sounds like you want some kind of load balancing mechanism. 
If it is really necessary for both systems to see a packet, then some form
of forwarding might be what you need. 

Hope this helps.

regards,

John Kelly
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Re: start up script

[Ray Olszewski]

As someone else already noted, this idea is not as straightforward as you 
might think it is. Offhand, I cannot think of a situation in which it is a 
good solution. But you know your actual problem better than I do, so let me 
tell you what I can about your questions, and leave it to you to decide.

At 02:43 AM 3/6/2004 -0800, Ravi Kumar Munnangi wrote:
>Users,
>
>   Iam working in a LAN with a number of systems.
>   A system has X hardware address and another has Y
>hardware address.
>   I want to set the hardware address of the second
>system
>   also to X.

OK. Whether you can do this or not is a hardware issue ... some NICs 
support it, but others do not. In any case, read the man page for 
"ifconfig" (or maybe "ip", if your system does not use ifconfig) to see the 
Linux part of this.

>   I also want to set the primary IP addresses of both
>   systems to 172.31.19.30.

OK. As you probably already know, you do this the same way you would set 
the machine to ANY IP address. The exact details are a bit distro 
spcecific, and you don't mention which Linux distro you are using ... you 
may use "ifconfig" directly, "ip" directly, or "ifup" in conjunction with a 
config file (usually /etc/network/interfaces).

>   So when I ping to 172.31.19.30, both the systems
>   should respond.

Yes, because ping is pretty good at handling multiple addresses, and icmp 
is "connectionless". Whether more complex and TCP-based protocols like http 
will also work in this setup is less clear to me ... I'd wonder if anyone 
has ever tried it (except as an accidental misconfiguration).

>   The topology of LAN we are using is star. All
>systems
>   are connected to a Switch.
>   Does the settings change when we are using a bus
>   topology?

Probably not ... but I am not certain what you mean by "bus" in this 
context. Are you referring to some sort of ring network (like an old-style 
thinnet LAN)?

>   Do I have to write a start up script?
>   How should I write?

These are distro-level questions ... and to some extent kernel level. Post 
a followup with the usual details on your setup ... what distro, what 
version, what kernel version, what NICs and modules ... and I or someones 
else might be able to answer this one.

>    My actual goal is to start 2 web servers on two
>   systems with same hardware address and same
>   primary IP address but with different secondary
>   IP addresses. So when a request comes from a
>   client, the request has to be seen by both
>   systems. I will write some mechanism by which only
>   one will respond finally.

Before you spend too much time on this approach, you want to think through 
the "some mechanism" piece. Hand waving won't do here, and I don't see a 
sensible way to create a mechanism that will work.

My best *guess* is that you want to do one of two things --

         1. Load balance -- in normal operation, have each server handle 
roughly half of the traffic.
         2. Failover -- in normal operation, have one server handle all of 
the traffic, but have the second ready and waiting to "hot swap" in if the 
first should fail.

Either of these needs can be achieved in other, more conventional ways than 
what you propose to try. The details depend on the content of the Web site 
... how much of it is dynamically generated, and how it is generated, how 
often its static content changes, how you intend to keep the two machines' 
versions of the Website in sync, and the like ... and may involve a third 
host (or even a fourth, if a large, shared database is involved).



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Re: start up script

[Stephen Samuel]

Ravi Kumar Munnangi wrote:
> Users,
>  
>   Iam working in a LAN with a number of systems.
>   A system has X hardware address and another has Y
> hardware address.
>   I want to set the hardware address of the second
> system
>   also to X.

ifconfig eth0 hw ether  00:56:BA:A4:81:02

>   I also want to set the primary IP addresses of both
>   systems to 172.31.19.30.
>   So when I ping to 172.31.19.30, both the systems
>   should respond.
ifconfig eth0 172.31.19.30   [[ may want to set netmask/BC]]
> 
>   The topology of LAN we are using is star. All
> systems
>   are connected to a Switch.
>   Does the settings change when we are using a bus
>   topology?
Some switches may get confused by having the same
MAC address on two ports... In somes cases, it may
only send a packet to one fo the machines (usually
the last one to use that MAC address))

>   
>   Do I have to write a start up script?
>   How should I write?
Write a regular shell script and then put it in
the proper place.  If you have proper rc2.d
script directories, then you can put it near the
SNNnetwork scripts

For RedHat, that would be /etc/rc.d/rc[2345].d/S10network
so you could try S09
Otherwise, put it in the r.local file for those kinds of systems.

Setting the MAC addr needs to be done *BEFORE* you
bring the card up. (or you need to bring it down).
(under Linux)

For RedHat systems, however, you can use the MACADDR=
variable in /etc/sysconfig/network-scripts/ifcfg-eth0
and IPADDR=

The RH scripts do the rest.



For the person who said that some cards don't support this,
I would say that that is very rare to nonexistent..
the MAC address needs to be softwar settable for
things like prosxy arp and bridgng... In 17 years
of playing with ethernet, Idon't rememember *ever* seeing
a card that you couldn't set the MAC address on.



>   My actual goal is to start 2 web servers on two
>   systems with same hardware address and same 
>   primary IP address but with different secondary
>   IP addresses. So when a request comes from a 
>   client, the request has to be seen by both 
>   systems. I will write some mechanism by which only
>   one will respond finally.


-- 
Stephen Samuel +1(604)876-0426                samuel@bcgreen.com
		   http://www.bcgreen.com/~samuel/
    Powerful committed communication. Transformation touching
      the jewel within each person and bringing it to light.
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