Re: Virtual Ethernet

[Pete Helgren <Pete@xxxxxxxxxx>]

The subnet tells the router/switch/network client whether the 
destination is in the same network or needs to be routed.  For example 
if you had a network IP address scheme that was 10.0.10.xxx and the 
subnet was 255.255.255.0.  The "255" values basically say to TCI/IP 
"Give me an exact match".  The 0 value says "Match anything".  And let's 
say the client has an address of 10.0.10.10.  If your target was 
10.0.10.100 with the given subnet of "0" then the client "knows" that 
the 100 address is on the same network and it doesn't have to go out the 
gateway in order to find the target.  Since both the client and the 
target reside on the same logical network (they are both on the 
10.0.10.xxx network, based on the subnet) the client (10) will assume it 
can contact the target (100) on the same network.  It won't attempt to 
go out the gateway to find the target computer. 

Leaving everything the same but change the subnet to 255.255.255.240 and 
now the client knows it CANNOT contact the target on the local logical 
network because the 240 subnet mask "masks" all IP's so that the 
10.0.10.10 client can only "see" IP addresses from 10.0.10.1 - 
10.0.10.14 because of the subnet it is on.  In fact, given the "mask" 
255.255.255.240, the "network" for the client becomes 
10.0.10.1-10.0.10.14.  It cannot get to any other addresses without 
going out the gateway.  This is all a "logical" networking scheme 
enforced by the TCP/IP stack, it has nothing to do with the physical 
connections between the two PC's.  Even if the two PC's were physically 
on the same hub/switch, they couldn't even see each other without 
routing.  This is the beauty of the TCP/IP stack.

I'll spare you the binary math that makes all this work but suffice it 
to say that the subnet mask "tells" the client/router/switch what 
network it is on so it know whether to route or not.  I won't go into 
network "Classes" which can further confuse at this point.  And, this is 
all very simplistic, leaving out many details.

If you need to see how each network is calculated, take a look at an 
online network calculator.  I found one here: 
http://www.subnet-calculator.com/

In this specific case, Bryan's suggestion to put your vlan on a 
completely different network IP scheme is a good one.  Your subnetting 
won't be as critical since the 10.xxx.xxx.xxx network is completely 
different than the 192.168.xxx.xxx network, they will HAVE to use the 
gateway to route and therefore you can use some routing entries to make 
traffic follow the routes you want (or not add any routing entries at 
all so they only see each other and nothing else).  Use subnet 
255.255.255.0 and the correct gateway and you should be good to go.  The 
two 10.0.0.xxx addresses should only find themselves on the same logical 
network and won't even attempt to route.

I hope this is of some help.

Pete Helgren

Ingvaldson, Scott wrote:
> I can try that, but Subnet Masks confuse me.  What can I use that will
> make ADDTCPRTE happy?
>
> I'm not sure how much growth to plan for, we have 4 LPARs now, but there
> is potential for more and I'd like to plan for 32 to be on the safe
> side.
>
> Regards,
>
> Scott Ingvaldson
> Senior IBM Support Specialist
> Fiserv Midwest
>
>
> -----Original Message-----
> From: bryan dietz [mailto:bdietz400@xxxxxxxxx] 
> Sent: Monday, January 21, 2008 10:05 AM
> To: Midrange Systems Technical Discussion
> Subject: Re: Virtual Ethernet
>
> I would try using an IP address range for the v-ethernet that is not
> close to your regular network.
>
> ie. if you have 192.168.x.x for regular incoming traffic try a
> 10.x.x.xaddress for the internal v-ethernet.
>
> I have even used 1.1.1.1 and 1.1.1.2 for the two partitions v-ethernet.
>
> Bryan
>
>
> On Jan 21, 2008 10:59 AM, Ingvaldson, Scott
> <scott.ingvaldson@xxxxxxxxxx>
> wrote:
>
>   
> > I'm "assuming" that's what is happening, but I'm not sure exacly how 
> > to prove it, short of a trace and I'm thinking that this should not be
> >     
>
>   
> > that hard to solve.  I can ping the 192.168 addresses from either LPAR
> >     
>
>   
> > but not from any network attached workstations (which is what I would
> > expect.)  I set up host table entries to point to the 198.162 
> > addresses and tried to set up a route to force the outgoing traffic to
> >     
>
>   
> > the virtual ethernet line, but could not due to msgTCP264F - 
> > SUBNETMASK parameter value not valid, RC0006 - The route does not have
> >     
>
>   
> > a subnet mask that masks the corresponding one bits in the host 
> > portion of the route destination.
> >
> > The LPAR IP addresses are configured as 192.168.10.xxx and I have 
> > tried subnet masks of 255.255.255.0, 255.255.0.0 and 255.255.254.0.
> >
> > Regards,
> >
> > Scott Ingvaldson
> > Senior IBM Support Specialist
> > Fiserv Midwest
> >
> >
> > -----Original Message-----
> > From: Pete Helgren [mailto:Pete@xxxxxxxxxx]
> > Sent: Friday, January 18, 2008 4:41 PM
> > To: Midrange Systems Technical Discussion
> > Subject: Re: Virtual Ethernet
> >
> > Any chance it is routing the long way around?  I don't know how your 
> > network is configured but I had one customer that was using the 
> > "external" ports rather than the V-lan.  I think we added some routing
> >     
>
>   
> > entries but I don't exactly remember.  Use traceroute to see if the 
> > route is OK?
> >
> > Pete Helgren
> >
> > Ingvaldson, Scott wrote:
> >     
> > > I'm trying to get virtual ethernet connectivity set up between LPARs
> > >       
>
>   
> > > on a 550 here.  We need to do a daily transfer of a 60 GB library 
> > > between LPARs.
> > >
> > > I created the resources and lines, gave them IP addresses,
> > > (192.168.10.xxx) varied them on and got them talking.  Unfortunately
> > >       
>
>   
> > > it doesn't seem any faster than it was before.
> > >
> > > This is the LIND on both sides:
> > >
> > > CRTLINETH LIND(VRTETH01) RSRCNAME(CMN13) ONLINE(*YES) +
> > >          VRYWAIT(*NOWAIT) MAXCTL(40) ADPTADR(*ADPT) +
> > >          EXCHID(0569D5FF) ETHSTD(*ALL) LINESPEED(1G) DUPLEX(*FULL) +
> > >          MAXFRAME(8996) SSAP((04 1496 *SNA)(12 1496 *NONSNA)(AA +
> > >          8996 *NONSNA)(C8 1496 *HPR)) THRESHOLD(*OFF) +
> > >          GENTSTFRM(*YES) LINKSPEED(*MAX) COSTCNN(0) COSTBYTE(0) +
> > >          SECURITY(*NONSECURE) PRPDLY(*LAN) USRDFN1(128) +
> > >          USRDFN2(128) USRDFN3(128) AUTOCRTCTL(*YES) +
> > >          AUTODLTCTL(1440) CMNRCYLMT(2 5) MSGQ(*SYSVAL) +
> > >          TEXT('Virtual Ethernet')
> > >
> > > An FTP using the new interface gave me this:
> > > 59497012608 bytes transferred in 4442.494 seconds. Transfer rate
> > > 13392.705 KB/sec.
> > >
> > > That's 74 minutes for 60 GB, is that a reasonable speed over virtual
> > >       
>
>   
> > > ethernet?  I can save it to tape faster than that.
> > >
> > > Regards,
> > >
> > > Scott Ingvaldson
> > > Senior IBM Support Specialist
> > > Fiserv Midwest
> > >
> > >       
> > --
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