[VLAN] VLANs and Network Emulation

[Hazelsnitzel]

At 10:24 AM 1/24/2007, you wrote:
>Hazelsnitzel wrote:
>>Greetings,
>>My task leader wants to use a 24-port Cisco Catalyst 2950 in 
>>conjunction with a Linux box to emulate multiple low-speed links, 
>>but I am too much of a novice at networking and VLANs to know 
>>whether his idea is feasible.
>>We currently emulate a single low-speed link by interposing a Linux 
>>box with two NICs between the endpoints on the link.  We use the 
>>Linux box as a bridge and use Linux traffic control (i.e., tc HTB 
>>or TBF) and "Netem" to emulate link characteristics. Eleven Linux 
>>boxes would be required to emulate 11 low-speed links.  My task 
>>leader's idea is to use a single "one-armed" Linux box and the 
>>24-port 2950 to emulate up to 11 links.
>>The intranet in our lab uses OSPF and we are not allowed to 
>>increase the number of router advertisements, so we can't use the 
>>Linux box as a router.  However, if this constraint were removed, I 
>>assume (#1) that we still couldn't use the Linux box as a router 
>>because both endpoints of each link are always in the same 
>>subnet.  Is this assumption correct?
>>I also assume (#2) that we can't use the Linux box as a bridge.  I 
>>assume that if the traffic emanating from the bridge were simply 
>>returned to it on a trunked link, it would only forward frames to 
>>the destination if the source and destination MAC addresses were in 
>>the same VLAN.
>>I would like to know if my two assumptions are correct and whether 
>>anyone has a suggestion about how to solve this problem.  Could it 
>>be done by developing some custom forwarding software?   If so, 
>>what would be required?
>
>It can be done.  We offer a product based on VLANs and our (non-open-source)
>network emulation tool.
>I'm not sure if netem can be used in bridge mode though...
>
>Here's a link to our 48-port network emulator product sheet (we offer other
>quantities of ports as well):
>http://www.candelatech.com/lanforge_v3/ct970_product.html
>
>The diagram shows one LANforge machine and one bridge machine, but we can
>now do all of this in a single machine for a more efficient use of hardware.
>
>If you are interested in more information related specifically to LANforge,
>please contact me directly (greearb at candelatech.com).
>
>Thanks,
>Ben
>
>
>>Thanks,
>>Bob
>>_______________________________________________
>>Vlan mailing list
>>Vlan at candelatech.com
>>http://www.candelatech.com/mailman/listinfo/vlan
>
>
>--
>Ben Greear <greearb at candelatech.com>
>Candela Technologies Inc  http://www.candelatech.com
>
>_______________________________________________
>Vlan mailing list
>Vlan at candelatech.com
>http://www.candelatech.com/mailman/listinfo/vlan


Ben,

Thanks for your reply.

My task leader has already purchased the Catalyst 2950 and a Dell 
PowerEdge so we need to try to make it work with this hardware.


                                       [ Catalyst 2950 ]
[ Linux Bridge ]--[eth0]--[trunked]---[ Port 1 ]
           +-------[eth1]--[trunked]---[ Port 2 ]
                                VLAN 2 [ Port 3 ]---- 192.168.2.3
                                VLAN 3 [ Port 4 ]---- 192.168.2.4
                                VLAN 4 [ Port 5 ]---- 192.168.3.3
                                VLAN 5 [ Port 6 ]---- 192.168.3.4
                                .....    .....         ..........

In this configuration, VLANs 2 and 3 emulate one link and VLANs 4 and 5
emulate another.

Will this configuration work?  Are there any adverse consequences to having
two trunked links as shown?

Regards,
Bob