The IP is full on VLAN

KFNAIT
KFNAIT used Ask the Experts™
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i have two vlans, vlan3 and vlan12 , I use 250 IP on vlan3, and i want to add new CISCO Switch 2950-48 port on vlan3, by free port, how can get new ip and what is the good configuration on the switch? and can i use the vlan12 on vlan3 and how?

The connection between VLAN3 and VLAN12 is CISCO ROUTER.



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If the 10.10.3.X subnet has a 24 bit mask, 255.255.255.0, then you don't have room to expand it and will need to add a new subnet on the router like 10.10.4.X. If the mask is 23 bits or less then you can continue assiging addresses from it. Either manually or via DHCP whatever you are using now.

You can't really use VLAN 12 on the new switch at that location because it is already in use with the 10.10.12.X subnet across the router at the other building.
Top Expert 2014

Commented:
Do you actually have 250 of the 254 IP addresses  in use, or is that just the possible IP address you can use?

As for the config for he new switch, it should be pretty much like the other 5 current switches in VLAN3.  All that really needs to be unique is the switch name and the management IP address.


To get additional IP space on a existing VLAN you can add a secondary IP address range to the
layer 3 interface. So, multiple IP ranges can operate out of the same vlan.

harbor235 ;}
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Top Expert 2007

Commented:
Provided that 10.10.2.0 is not in use, one option would be to change the mask to 255.255.254.0  which would change the address range to include 10.10.2.0 - 10.10.3.255

Author

Commented:

i already use 250 of the 254 IP addresses on VLAN3>>>

Is there any config on new switch to get the free IP on VLAN12 like 10.10.12.xxx
Top Expert 2014
Commented:
Which Cisco router do you have?

What you might be able to do is confgiure the Cicso router so that it can do VLAN tagging and configure each interface as a trunk link.

Configure each switch so that the interfaces that connect them to the Cicso router is a trunk link that supports both VLAN3 and VLAN12.

Then on some of the switches in the building that has VLAN3 it in you can configure a few of the ports as access mode ports on VLAN12.

However, depending on what the links are between the switches and the routers you could run into some problems.

What I personally would do is create a new VLAN in the building that has VLAN3 in it, say VLAN4 ip subnet 10.10.4.0/24.

That way you don't have broadcast traffic flowing between the two buildings.

Creating a new VLAN is really no more work than trying to get VLAN12 to cross buildings and will cause fewer performance problems.

Author

Commented:

Which Cisco router do you have?

C6509
Top Expert 2014

Commented:
O.K., I would create a new VLAN and use it instead of attempting to extended VLAN12 between the two buildings.

Author

Commented:
good
 
i do this config on the port 0/24 of switch which connected to the router.

switch:
int Fas 0/24
 switchport trunk allowed vlan 1,5
 switchport mode trunk
 load-interval 30
 spanning-tree portfast trunk

and i config the new switch like this>>

switch:
int Fas 0/24
 switchport mode trunk
 spanning-tree portfast trunk

and worked very well

BUT>

when i try to do the same config to new switch on another vlan, i can not get ip
Top Expert 2014

Commented:
How is the new switch connected?

Is it connected directly to your 6500?  If so, did you make the port it connected to a trunk port?

Author

Commented:

The new switch connected to the another switch which is connected directly to 6500 by Fiber ...

and i make the connect between the switches trunk port.
Top Expert 2014
Commented:
O.K., so you have

6500 <--> Existing Switch <--> New Switch

You need to make sure that the connection between the Existing Switch and the new Switch is either a trunk port that supports all of the VLAN you want to flow to the new switch or an access mode switch whose is on VLAN 5.

Where is the DHCP server for VLAN 5?  Are you using the 6500 or something else?  

If you are using something else, is it on VLAN 5?

If not then, in the 6500's VLAN5 interface definition you need to code ip helper-address x.x.x.x where x.x.x.x is the IP address of the DHCP server that will be handing out the IP addresses for VLAN 5.

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