[LARTC] load sharing: ARP problem

[LARTC] load sharing: ARP problem

[Ojasi]

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Hello,
 
I have some questions regarding load-sharing in the following scenario.
 
------------------------------------------------------------------------------------LAN1
  |                              |                                   |
eth0                         eth0                              eth0
(PC1)                       (PC2)                            (PC3)
eth1                          eth1                               eth1
  |                               |                                     |
----------------------------------------------------------------------------------- LAN2
 
Each machine has 2 ethernet cards but single IP address.
For each machine, eth0 and eth1 are in active-active mode for load sharing and are on different LANs
In this case, how to solve the ARP problem.
I tried to look for many available solutions on net regarding this. But could not find any perfect solution. Most of the solutions offer active-standby but not active-active.
Can anyone help in this case ? how to deal with ARP problem and achieve load sharing ? 
 
Thanking you in advance.
Ojasi


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Re: [LARTC] load sharing: ARP problem

[Ard van Breemen]

On Tue, Aug 19, 2003 at 11:33:47AM +0100, Ojasi wrote:
> I have some questions regarding load-sharing in the following scenario.
>  
> ------------------------------------------------------------------------------------LAN1
>   |                              |                                   |
> eth0                         eth0                              eth0
> (PC1)                       (PC2)                            (PC3)
> eth1                          eth1                               eth1
>   |                               |                                     |
> ----------------------------------------------------------------------------------- LAN2
>  
> Each machine has 2 ethernet cards but single IP address.
> For each machine, eth0 and eth1 are in active-active mode for load sharing and are on different LANs
> In this case, how to solve the ARP problem.
> I tried to look for many available solutions on net regarding this. But could not find any perfect solution. Most of the solutions offer active-standby but not active-active.
> Can anyone help in this case ? how to deal with ARP problem and achieve load sharing ? 

Depends on what you are trying to do...
The load sharing of what?
If you need the loadsharing of routing, you need to configure
each card with the same mac-address, and configure your switch to
have a lag on those ports....

If you need to share the load of a webserver f.i., then take a
look at keepalived...
-- 
mail          up      14:42,     7 users,  load 0.01, 0.02, 0.00
mistar1     down   45+00:24
Let your government know you value your freedom: sign the petition:
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Re: [LARTC] load sharing: ARP problem

[Ojasi]

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Hi,
 
Thanks for the reply.
yes and  sorry I forgot to mention that it is about load sharing of routing and not webserver.
If I use same MAC addresses, then it will be a problem when there is a connection between switches. (that's why linux-bonding driver does not help in this case as it forces to use same MAC addresses)
Also, I did not understand "configure your switch to have a lag on those ports...."
One ethernet switch connects all eth0 ports and other switch connects all eth1 ports as shown in figure in previous mail. So, could you please explain little more about how the configuration of switch to add lag should be used ? 
 
Thanks and Regards,
Ojasi


Ard van Breemen <ard@kwaak.net> wrote:
On Tue, Aug 19, 2003 at 11:33:47AM +0100, Ojasi wrote:
> I have some questions regarding load-sharing in the following scenario.
> 
> ------------------------------------------------------------------------------------LAN1
> | | |
> eth0 eth0 eth0
> (PC1) (PC2) (PC3)
> eth1 eth1 eth1
> | | |
> ----------------------------------------------------------------------------------- LAN2
> 
> Each machine has 2 ethernet cards but single IP address.
> For each machine, eth0 and eth1 are in active-active mode for load sharing and are on different LANs
> In this case, how to solve the ARP problem.
> I tried to look for many available solutions on net regarding this. But could not find any perfect solution. Most of the solutions offer active-standby but not active-active.
> Can anyone help in this case ? how to deal with ARP problem and achieve load sharing ? 

Depends on what you are trying to do...
The load sharing of what?
If you need the loadsharing of routing, you need to configure
each card with the same mac-address, and configure your switch to
have a lag on those ports....

If you need to share the load of a webserver f.i., then take a
look at keepalived...
-- 
mail up 14:42, 7 users, load 0.01, 0.02, 0.00
mistar1 down 45+00:24
Let your government know you value your freedom: sign the petition:
http://petition.eurolinux.org

Win TVs, Bikes, DVD players and more!Click onYahoo! India Promos

[-- Attachment #2: Type: text/html, Size: 2831 bytes --]

Re: [LARTC] load sharing: ARP problem

[Ard van Breemen]

On Tue, Aug 19, 2003 at 01:32:58PM +0100, Ojasi wrote:
> yes and  sorry I forgot to mention that it is about load
> sharing of routing and not webserver.

Allright.
First of all: I cannot think of a case when a single linux box is
not fast enough to route. So I assume you have hit the wirespeed
in routing. Or your packets are plain to small. (Like haveing
about 130000 packets per second or so....)

> If I use same MAC addresses, then it will be a problem when
> there is a connection between switches. (that's why
> linux-bonding driver does not help in this case as it forces to
> use same MAC addresses)

Well, there you have the problem: how are you going to do
transparent route loadbalancing, if you don't want the switch to
co-operate?

> Also, I did not understand "configure your switch to have a lag
> on those ports...."

LAG is the IEEE term for bonding (linux), teaming (intel et
others), etherchannel (cisco), trunk (sun), etc...
It means that you have multiple ports acting as one big port...
But don't be fooled:  having 4 ports does not mean you have
quadrepled your throughput: to make sure that packets are sent
in the right order, the switches use a hash: there is only on
route for a specific source-destination mac, it always goes out
over the same port.

> One ethernet switch connects all eth0 ports and other switch
> connects all eth1 ports as shown in figure in previous mail.
> So, could you please explain little more about how the
> configuration of switch to add lag should be used ? 

Come to think of it: you can fix it:
You either have to answer arps using a hashing algorithm if that
is possible (I've seen some arp support in iptables now, but I
don't know if that works...).
If that does not work: you can use a multicast address for the
ip address (and yes, make them al the same), and use a blocking
mechanism on ip level...

Anyway: your tasks to figure out what is ok:
- learn what arp is al about: mac-address vs ip address
- Learn something about lag...
- Look at iptables if it supports blocking of arp-requests...
-- 
mail          up      16:33,     7 users,  load 0.00, 0.05, 0.04
mistar1     down   45+02:14
Let your government know you value your freedom: sign the petition:
http://petition.eurolinux.org

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Re: [LARTC] load sharing: ARP problem

[Bart De Schuymer]

On Wednesday 20 August 2003 11:53, Ard van Breemen wrote:
> Anyway: your tasks to figure out what is ok:
> - learn what arp is al about: mac-address vs ip address
> - Learn something about lag...
> - Look at iptables if it supports blocking of arp-requests...

You'll want to look at arptables for filtering arp stuff, see 
ebtables.sourceforge.net

cheers,
Bart

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