make 48-port switch look like two 24-port swi

Netgear / Gsm7352 sv2
May 5, 2011 at 09:43:50
Specs: 8.0.3.15
make 48-port switch look like two 24-port switches

Creating two switching VLAN's 1(default) with only odd # ports and 2 (with only even # ports) all DHCP bootpc broadcasts get moved from VLAN 2 to VLAN 1. No system on VLAN 2 sees the boradcasts. Any system on VLAN 1 sees the broadcasts. DHCP on VLAN 1 works fine. DHCP on VLAN 2 doesn't work because the DHCP server for VLAN 2 never sees the requests. What am I going wrong?


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#1
May 5, 2011 at 09:48:36
dhcp server port needs to be in both vlans

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#2
May 5, 2011 at 09:55:32
Each VLAN is connected to a different subnet. I have two (2) DHCP servers, one (1) on each subnet. I have no control over that situation. I need the two VLAN's to be segregated from each other. I have several Linux systems that need to connect to each subnet and get their IP's assigned from the respective DHCP servers (which I don't control). I need to stop the NetGear switch from getting the DHCP broadcasts on one VLAN and routing them to just the default VLAN.

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#3
May 5, 2011 at 11:51:45
Only question then is why the one dhcp server isn't working.
Might want to use wireshark at each end to determine if dhcp packets are getting thru.

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#4
May 5, 2011 at 12:05:44
The second DHCP server is on VLAN 2. From any system hooked to VLAN 2 I can run tcpdump and watch what goes on the wire. From a second window on that system I can run dhclient eth1 (eth1 is connected to a port in the switch that is in VLAN 2). I see the broadcast (255.255.255.255.bootpc) going on the eth1 wire (I can run a thrid window and watch eth0 and no broadcasts go onto eth0).

From another system hooked to VLAN 2 I can run tcpdump and I never see the dhcp broadcasts. From a system hooked to VLAN 1 I can run tcpdump and there I see all the DHCP broadcasts.

The switch is intercepting the broadcasts and routing them onto VLAN 1.

If I had been involved in the purchase decision I would have voted to purchase two (2) switches and this problem would have been solved (actually it would have never been a problem). I wasn't involved in that decision.

I found a 4 port switch lying around the lab and connected it as the second switch to the VLAN 2 ports on three (3) of the machines and the subnet that connects the second DHCP server and *poof* it works. Unfortunately, I need 20+ ports.



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#5
May 5, 2011 at 12:43:45
This a layer 3 switch?

disable vlan routing would be the next step.

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#6
May 5, 2011 at 13:39:14
It says it is yes

NetGear gsm7352 Sv2


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#7
May 6, 2011 at 07:25:47
This should be a fairly simple setup to configure.

You have two VLAN's and are allotting 24 ports to each VLAN.

The uplink cables for the two VLAN's should be plugged into a member port of their associated VLAN. Which is to say:

VLAN 1 = odd numbered ports
Uplink port = port 1

VLAN 2 = even numbered ports
Uplink port = port 2

Not being familiar with that particular switch, all I can tell you is to make sure you have your uplink's plugged into the correct ports because it sounds like maybe you' haven't.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#8
May 9, 2011 at 07:11:38
I completely agree this should have been a simple problem to solve.

VLAN 1 = odd numberd ports
uplink port = 23

VLAN 2 = even numbered ports
uplink port = 24

I asked two others to verify the cabling and look at my attempts to VLAN the switch. They are as puzzled as I am about what's going on.


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#9
May 9, 2011 at 07:29:34
And yet, you take the VLAN 2 feed, plug it into an unmanaged switch and it works. I confess, this has me stumped.

The only thing I can think of is that perhaps the switch itself is the issue. It shouldn't be, but maybe it is?!?!?!

Perhaps with the switch you're using you have to use a single uplink configured as a "trunk" port in order to have both VLAN's work correct.y This doesn't make any sense to me, but it would be one thing to try if you haven't already.

Alternatively, you might want to trade VLAN's. Since the clients are DHCP, just swap the feeds. Do clients on VLAN 1 get proper IP's in the VLAN 2 subnet? Do the clients plugged into VLAN 2 ports get anything?

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#10
May 9, 2011 at 08:31:20
It's a head scratcher.

I have a second switch that I'm going to install and see if I can get that to work. As a long term solution it's not viable, BUT it might shed some light on the situation??

Appreciate the responses. I don't think I'm as totally lost as I was beginning to fear.

Thanks,
Paul


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#11
May 9, 2011 at 09:56:57
I would definitely try swapping the feeds as I suggested and see what happens.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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