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DHCP to a specific switch and or VLAN

jeeperyj
jeeperyj asked
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My goal is to have our 3com network switch hand out a specific scope I created in DHCP.   We have old 3com equipment and the documentation for it is awful.  My first idea, was to create a vlan on our core switch (a 3com 4050) and then assign the vlan an ip address.   After hours of searching i feel it can't be done.  With that said, I created a VLAN 88 on my core switch and added a port to it.  I then connected that port to an old 3300 3com switch.  I then setup a DHCP scope (on our dhcp server)  for 10.10.88.x for the new switch.  I changed the switches default management IP to 10.10.81.1, etc.

When I plug in a pc I get our normal dhcp addresses.  How can I force this switch to use the new scope?  

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Commented:
Hi, On the core, you should create your vlan VLAN88 and then give it an IP address and subnet mask. The ip address given should be thought of as the default gateway. so 10.10.88 254 and mask of 255.255.255.0 for example.
The range on the DHCP server should be set to 10.10.88.5-250 for example. The scope Options for Router should be your default gateway so in your case 10.10.88.254 and specify your DNS server.

Any traffic coming from that switch will come throught 10.10.88.254 interface and the DHCP server will know that and address accordingly.

Can you confirm this is how it's setup?

Cheers, Graeme

Author

Commented:
Part of the problem is I cannot locate a way to add IP info for the Vlan on our core switch. (the 4050)

I was doing some more investigating and noticed our 3750 cisco switch (we use this as a router pretty much)
has the following for an existing vlan..



 interface Vlan51
 ip address 10.10.51.1 255.255.255.0
 ip helper-address 10.10.10.25
!
Should I try to add an entry for my new Vlan88

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Commented:
Absolutely.... and yes include the helper address which I assume is your DHCP address?
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Commented:
Though it may not be your DHCP address of course :o)

Author

Commented:
ok, I changed my plan, I now created a vlan 88 on the 3750, added ip info as 10.10.88.1 and 255.255.255.0

I then added a ip-helper of 10.10.10.25 (our dhcp server)

I can't ping 10.10.81.1 nor does it hand out dhcp on that port..  

Author

Commented:
I take that back, 10.10.81.1 is now pinging
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Commented:
Cool. Why use .1 most gateways are .254 on a /24 network but you can anything. JuSt good practice that's all.

Author

Commented:
They made them all .1 around here I guess..

here is the helper statement I made

interface Vlan88
 ip address 10.10.88.1 255.255.255.0
 ip helper-address 10.10.10.25
!

!


then the interface port is config like this

interface GigabitEthernet1/0/5
 description image
 switchport access vlan 88
 switchport mode access
 switchport port-security aging time 2
 switchport port-security violation restrict
 switchport port-security aging type inactivity
 macro description cisco-desktop
 spanning-tree portfast
 spanning-tree bpduguard enable

show vlan
51   Graphics                         active    Gi1/0/4
88   IMAGE                            active    Gi1/0/5



I have that port going right to my laptop and I do not get dhcp...



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Commented:
I assume your laptop is set for dhcp client! Is your dhcp zone enabled for vlan88? I'm not a cisco guy but the configs seems ok to me if its already a router and set to be a router.  What address is laptop getting? None? Can you ping interface .w still? Can you ping dhcp server?

Author

Commented:
It is, it hands me the 169 address...  

I checked this on the switch with an ip route..   I am at a loss.  

I did config a static address and it wont ping 10.10.88.1 but on my normal network subnet, I can ping 10.10.88.1  



   10.0.0.0/8 is variably subnetted, 15 subnets, 2 masks
C       10.10.8.0/22 is directly connected, Vlan1
C       10.99.99.0/24 is directly connected, Vlan99
C       10.10.12.0/24 is directly connected, Vlan2
C       10.10.13.0/24 is directly connected, Vlan3
C       10.10.14.0/24 is directly connected, Vlan4
C       10.10.15.0/24 is directly connected, Vlan5
D       10.10.22.0/24 [90/3072] via 10.10.10.252, 3w0d, Vlan1
D       10.10.24.0/24 [90/3072] via 10.10.10.252, 3w0d, Vlan1
D       10.10.25.0/24 [90/3072] via 10.10.10.252, 3w0d, Vlan1
D       10.10.26.0/24 [90/3072] via 10.10.10.252, 3w0d, Vlan1
C       10.10.48.0/24 is directly connected, Vlan48
C       10.10.49.0/24 is directly connected, Vlan49
C       10.10.50.0/24 is directly connected, Vlan50
C       10.10.51.0/24 is directly connected, Vlan51
C       10.10.88.0/24 is directly connected, Vlan88
C    192.168.100.0/24 is directly connected, Vlan20
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Commented:
Are there lights on the port interface? It's not in shutdown mode is it? use the no shutdown command. Or sh int G1/0/5. Doubtit's shutdown if you can ping from other networks though

can you confirm laptop client set to:
ip address 10.10.88.2 or whatever
mask 255.255.255.0
default gateway 10.10.88.1

and you still can't ping the gateway from firewall? Does that laptop get an address plugging into another network outlet?

Laptop firewall?






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Commented:
Is it a windows DHCP server? You may need to restart the service if not.

Do you have wireshark or a sniffer you can use to see what the dhcp conversation is like?

Author

Commented:
Yep there are lights on the port, and the NIC detectes a gb connection.  It is a windows server too.  I confirmed my static address was 10.10.88.3, 255.255.255.0 and gw of 10.10.88.1 and can't ping 10.10.88.1 from the laptop..   Very strange..when I remove the static, and try dhcp, it goes back to the 169 address...

I am completely stumped
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Commented:
Can the laptop get an address from the normal network? Need to rule out laptop IP issues first

Author

Commented:
For more troubleshooting, I re-assigned an ip to the vlan (I made it 10.10.88.254)  I wanted to make sure there wasn't some other device answering on 10.10.88.1, and there wasn't.  It now answers on .254

Author

Commented:
Yes the laptop grabs an IP perfectly from the main network..
Commented:
figured it out,  that port was in monitor mode,  removed that and it all worked.

Thanks everyone!
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Commented:
Yay :o)


Ernie BeekSenior infrastructure engineer
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Commented:
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