With the changes suggested I was able to talk to UML instances on
multiple hosts. Thanks for your support.

But I have new issue now. I have an 2 UML instances running on 2
hosts. My application runs on both UML instances and syncs huge data.
The data syncup wasn't successfull. I see the following error message
on the host machine console:

 Packet length errorsize 4094 expected size 18178

I tried to bring up my app on host machine and the syncup is perfect.
I just wanted to check whether this is caused by vde switch/tap
interface(MTU) overhead. Any ideas?

Regards,
Sirisha

On Wed, May 5, 2010 at 11:51 AM, Daniele Lacamera
<danie...@users.sourceforge.net> wrote:
> Sirisha Alla wrote:
>>
>> Hi,
>>
>
> Hello.
>>
>> I was trying to use vde_switch utility and form a virtual network for
>> UML instances running on multiple hosts.
>>
>> Here is my configuration:
>>
>> Two linux machines: (host1)10.130.130.180, (host2)10.130.131.90
>>
>> On host1 did the following:
>>
>> 1) created tap0 and assigned 192.168.0.254
>> 2) ran vde switch with the following commands: vde_switch -tap tap0
>> -daemon -s /tmp/switch -unix /tmp/switch/ctl
>>
>>
>
> you are duplicating the same option twice, that should not happen.
> Either use -unix or -s, ensure that /tmp/switch is not already there.
> From now on, I will assume your switch command line is just "vde_switch
> -tap tap0 -daemon -s /tmp/switch"
>>
>> On  host2 did the following:
>>
>> 1) created tap0 with192.168.0.100 ip address
>> 2) ran vde switch with the following commands: vde_switch -tap tap0
>> -daemon -s /tmp/switch -unix /tmp/switch/ctl
>>
>>
>
> same mistake here  ^^
>
>> - Created vde cable using dpipe vde_plug /tmp/switch/ctl = ssh host2
>> vde_plug /tmp/switch/ctl on host1 and dpipe vde_plug /tmp/switch/ctl =
>> ssh host1 vde_plug /tmp/switch/ctl on host2
>>
>
> Do you use two cables to connect two switches each other in real life
> :)? Every dpipe is bidirectional, so you just need one cable with two
> plugs. Try just "dpipe vde_plug /tmp/switch = ssh host2 vde_plug
> /tmp/switch" on host1, and be careful to use the same path you passed in
> switch creation ('ctl' is not needed, vde plugs detect control port
> automatically). Also, if you used tap on both sides, you will be able to
> ping the machines on the vde network.
> Simply pinging 192.168.0.100 from host1 should work at this point, and
> should allow you to test your virtual network on your real hosts, before
> actually starting the two guest machines.
>
> Also, consider using an alternative cable: vde_cryptcab for better
> network performance, or udp netcat for best if authentication and data
> confidentiality are not in your primary goals, (i.e. your real network
> is your LAN). Refer to manuals or find a tutorial on
> http://wiki.virtualsquare.org/.
>
> As last optimization, to avoid IP fragments, shrink your tap and UML eth
> MTUs to something (50 Bytes) less than the real network  ones, to allow
> a cleaner encapsulation of 'virtual' ethernet frames into 'real'
> transport payloads.
>
> [uml stuff following]
>>
>> I will be happy to provide suggested logs if additional information is
>> required. My requirement is that both 192.168.0.1 and 192.168.0.3
>> should see each other.
>>
>> Regards,
>> Sirisha
>>
>
> HTH
>

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