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Managed Configure VLAN, Unable to Issue DHCP out

Posted on 2008-10-13
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Last Modified: 2011-10-19
Currently I POCing Fortigate UTMS with plan to split company network to several vlan for ease of management. I got 3 3COM Switch 4400 SuperStack 3 3C17203 aggregated together into 1 VLAN. To start the test small, I configured 2 free ports on of the switch into VLAN 2  and configured the DMZ port on the Fortigate firewall to issue DHCP. I tested it with a cross cable connect to my laptop the DHCP issue is with no issue. I connect cross cable from the Fortigate DMZ  to one VLAN 2 port while the other VLAN 2 port is connected to the test laptop.

I can ping to the dhcp server using static ip neither can I grab any ip from the dhcp server set at the fortigate DMZ port. Any 3COM switch experts out there can lend me a hand. Thanks.
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Question by:aneky
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22 Comments
 
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from_exp earned 500 total points
ID: 22709139
Hi!
I know 3com 4400 rather well, however I can't remember any feature in it to block some traffic. Try to use unmanaged switch to check this. My initial assumption is incorrect switch config (check if both ports added to this vlan 2 untagged) and check fortigate for logs. try also to release ip on client and then to renew it.
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by:aneky
ID: 22709477
Actually I installed the 3com Network Device Manager login into the 3COM switch and configured the VLAN to both tagged or untagged, without any luck. If it doesn't ping to the fortigate gateway the issue should lie on the 3com switch. I enclosed the screenshot of my config in here for a look.

One thing need to note is if I access directly to the switch using IE, I will not be able to see the VLAN configuration as I see in 3com Network Device Manager. I no idea if it is because of the firmware of the switch might be obsolete that causes this issue.


VLAN-Config.JPG
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by:from_exp
from_exp earned 500 total points
ID: 22709595
try to configure vlans using console/telnet - it is rather straight forward
both ports should be untagged in vlan 2 with pvid 2, as you have on the picture.
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by:aneky
ID: 22709628
Problem it doesn't work as it should. Unless, you wan me connect 1 pc at 1 port with pre-assigned IP and another with the same and try ping to each other to isolate maybe the problem might be at the fortigate portion.
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by:aneky
ID: 22709656
I telnet into the switch I checked the vlan settings still there. as I configured using the GUI.
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by:from_exp
from_exp earned 500 total points
ID: 22709664
sorry, but can you, please, connect to the switch with telnet and verify if there is vlan 2 and it is assigned to correct ports
and if there isn't then try to create it
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by:aneky
ID: 22709712
Yeah I just did as you ask when I post the previous message. Let me enclosed screenshot to explain it better.


TELNET-VLAN-Config.JPG
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by:from_exp
from_exp earned 500 total points
ID: 22709883
ok, seems you have vlan 2 on the switch.
now, please, connect both devices and check ports status. if ports are enabled and marked as active, check mac addresses learned by switch on those ports and in vlan 2
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by:from_exp
from_exp earned 500 total points
ID: 22709889
it is also useful to check if both ports (and both network cards) are configured with auto negotiation
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by:aneky
ID: 22709978
How to check if both ports are configured auto negotiation. I thought by default all switch port is configured for auto negotiation
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by:from_exp
ID: 22710016
in the ports menu via telnet, however, if both ports are active (green led), then port is up with correct settings.
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by:aneky
ID: 22717459
If that the case both ports are up with green led, but I cannot ping to the the fortigate. I manually configure the 2 static ip on 2 laptop within the same subnet and ip range (with firewall and antivirus disabled) and tried ping to each other. Both reply with timeout. I running out of ideas what going wrong with the vlan.
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by:from_exp
ID: 22718241
please issue arp -an on both laptops - I want to check whether pc's can get macs of the second side
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by:aneky
ID: 22718286
When I run the command arp -a on  both laptop. The laptop configure with the IP 192.168.1.4 respond

Interface 192.168.1.4 ---- 0x3
   Internet Address            Physical Address                  Type
   192.168.1.5                    00-00-00-00-00-00                invalid

The laptop configure with IP 192.168.1.5 respond

There are no arp entries.

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by:from_exp
ID: 22718497
so it means, you don't have both ports in the same vlan.....
is it possible you are using incorrect ports/unit?
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by:aneky
ID: 22718533
No I specifically configure it under unit 1 port 4 & 8. If they are not in the same VLAN 2 then if I use a laptop plug to the port I should able to grab the IP from the original VLAN 1. I had tried both ports are unable to grab IP from my DHCP server.
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by:from_exp
ID: 22718585
yes, but from the other hand if those ports are within the same vlan, pcs should be able to see each other.
can you reboot your stack?
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by:aneky
ID: 22718623
I will have to wait after office working hour to do that. If reboot is the only choice.
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by:from_exp
ID: 22718627
if you say that you have created vlan, and assigned ports to it and it still not working - I would try rebooting device....
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by:aneky
ID: 22754914
Ok I rebooted the switch. The problem still persist. arp -a still unable to see each other neither can ping or grabing IP from the dhcp server.
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by:from_exp
ID: 22755090
hmmmmm
please, check mac addresses learned by switch on both ports.
do both macs are within the same vlan?
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by:aneky
ID: 23033344
from_exp

Thanks for your help. The problem still the same. Anyway, I give up on the VLAN as my management pull the plug on my network upgrade plans so I no longer need this .
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