Separate VLANS on same subnet causing problems.

I don’t know that this is going to work quite like you anticipate it to. If this switch is acting as your layer 3 switch, you wont be able to place the same subnet on multiple VLANs, you will receive an error. If the switch is working in Layer 2 mode, you may theoretically be able to get it to work, but it sure would not be what is recommended.

How is this being cabled together? Is this switch layer 3 or 2?

Routing has to be enabled on the switch, it is not enabled from the factory. Can you post up your running config along with which ports on the 6248 plug into which devices. I can't guarantee this will work, but we can try. What else does your load balancer plug into?

Thanks for the extra info, that configuration is how i would set things up if i were to try this. I don't see any changes you could make to the configuration that would change the behavior. If the network load balancer is only connected to the 6248 and nothing else, what purpose is it serving on the network?

Here is the config.

Internet -> (port2 on 6248) (port 12) -> firewall -> (port13 on 6248) -> (port 24 on 6248) ->port 1Load blancer port2 -> (port25 on 6248) -> webs server on port 26 on 6248.

VlanA port2-12

VlanB port13-24 (except 47+48)

VlanC port25-48 (except 45+46)

!Current Configuration:
!System Description "PowerConnect 6248, 3.3.8.2, VxWorks 6.5"
!System Software Version 3.3.8.2
!Cut-through mode is configured as disabled
!
configure
vlan database
vlan 2-4
exit
stack
member 1 2
exit
ip address 10.0.0.1 255.0.0.0
ip default-gateway 10.150.0.1
interface vlan 2
name "clientside"
exit
interface vlan 3
name "serverside"
exit
interface vlan 4
name "outside"
exit
username "removed from post"level 15 encrypted
monitor session 1 destination interface 1/g12
monitor session 1 source interface 1/g2
monitor session 1 source interface 1/g3
monitor session 1 source interface 1/g4
monitor session 1 source interface 1/g5
monitor session 1 mode
!
interface ethernet 1/g1
mtu 9216
exit
!
interface ethernet 1/g2
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g3
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g4
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g5
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g6
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g7
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g8
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g9
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g10
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g11
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g12
mtu 9216
switchport access vlan 4
exit
!
interface ethernet 1/g13
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g14
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g15
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g16
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g17
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g18
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g19
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g20
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g21
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g22
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g23
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g24
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g25
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g26
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g27
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g28
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g29
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g30
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g31
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g32
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g33
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g34
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g35
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g36
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g37
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g38
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g39
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g40
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g41
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g42
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g43
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g44
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g45
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g46
mtu 9216
switchport access vlan 2
exit
!
interface ethernet 1/g47
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/g48
mtu 9216
switchport access vlan 3
exit
!
interface ethernet 1/xg1
mtu 9216
exit
!
interface ethernet 1/xg2
mtu 9216
exit
!
interface ethernet 1/xg3
mtu 9216
exit
!
interface ethernet 1/xg4
mtu 9216
exit
enable password a1208ed11204cad632d752adbcd68ae8 encrypted
exit

The load balancer is not connected to anything else.  port1 is upstream and port2 is downstream to the servers.

I'll post the config soon.

Victor

Hi,

Firstly, thanks for your reply.  

The 6248 by default layer 3 from the factory?.  How does one place this switch into layer 2 mode?

It's being cabled together in a flat network.  Internet -> Vlan1 -> firewall -> Vlan2 -> Port1 on Load Balancer port2  ->Vlan3 -> servers.  Vlan2 and Vlan3 need to be on the same network but the only device between them is the load balancer.

Regards,

Victor

Correction, firewall public side is connect to port 11 on 6248 as port 12 is the destination to the mirrored ports 2,3,4,5.

Web servers are unreachable when the last VLAN is connected to the web servers.  Only when I use a separate switch, it works.

Victor

The load balancer sits in between the web servers and the rest of the network.  It listens for HTTP requests on port 1 and distributes the load on port2 where the servers are located.

There are other minor servers connected right behind the firewall so there needs to be a Vlan in the "middle"

IF there were any traffic "leaking" between the last 2, I'd think there would be a network loop as you could just pretend the load balancer as a piece of network cable.

Victor

Alteon 184.

I'll do some tests monday.  It's a production environment so I can't experiment too much.  I'll first see if I have enough equipment to reproduce this in a lab environment.

Maybe I'm just grasping at straws...but....

I wonder if the load balancer gets confused with MAC addresses.  Will each VLAN have the same MAC address? So port1/2 (upstream and downstream) on the load balancer see the same MAC on the 2 ports and just get confused.

 Anyways, thanks for all the help so far.  It's giving me ideas.

Regards,

Victor

What brand/model is the load balancer being used? If you take the load balancer out and put a cable in its place, does traffic flow?

Thanks for keeping us updated, sorry this wont work how you would like.

Hello,

A quick answer would be to ensure that your switch does not have ip routing enabled.

Without IP routing the switch is just layer 2, and you might be able to do what you are trying.

If you have IP routing enabled:

This will not work for multiple reasons. While having same subnets on different vlan's is possible(at layer 2, only MACs matter IP doesn't come into play). The problem comes into play the moment you have to do routing. you can't have same subnets on more than 1 port of the router.

If your try doing inter-vlan routing on the switch it won't work.

If your try routing through firewall, it still won't work.

Think of it this way, traffic from 10.*.*.1/8 doesn't need routing to get to 10.10.*.1/8 but traffic from 10.10.10.1/24 will need routing to get to 10.10.20.1/24

Your problem might go away if you narrow down your network to /24 or something like that.