ICND2 - vlans keep changing to admin down

Hi Everybody,
This is frustrating and fascinating. I am practicing ROAS. I am trying to use two vlans on a 2950: VLAN09 (int fa0/9) and VLAN10 (int fa0/10). When I 'no shut' one of them, the other automatically clicks to admin down! Please advise. Thanks!

Find more posts tagged with

Free for TechExams community: Cybersecurity salary guide

Compare cert salaries and plan your next career move

Button

Comments

Adam B

Please post some of your configs and I can see where the problem may lie. I was just wondering though, do you have separate subinterfaces on the router for the vlans? If so are they in the same subnet or different subnet? And I'm pretty sure you don't even have to do a no shut, just do "vlan ___" and itll go up, unless of course you shut it down yourself.

mikeybinec

My guess is you have assigned IP addresses to both VLANs on the same switch--which you can't do. But as Adam sez, post your running-config

RouteMyPacket

2950 = L2

You cannot have two IP's on this switch. The Router is where the L3 SVI's are to be configured and is of course where the inter-VLAN routing will take place.

You Trunk to the router from the switch and allow whichever L2 vlans across the trunk

MAC_Addy

mikeybinec wrote: »

My guess is you have assigned IP addresses to both VLANs on the same switch--which you can't do.

Really? Since when? Now a 2950 is a L2 device, so you cannot. You can't actually assign an IP address to a VLAN via the switch, but you can via the router.

mikeybinec

MAC_Addy wrote: »

Really? Since when? Now a 2950 is a L2 device, so you cannot. You can't actually assign an IP address to a VLAN via the switch, but you can via the router.

I've made that mistake before. I assigned an IP address to two diff vlans ON THE SWITCH, and one would shut down and the other would stay up..Thus my guess.

Node Man

update: even when a switch is used, just by itself, the bizarre Admin Down change still happens.

mikeybinec

Node Man wrote: »

update: even when a switch is used, just by itself, the bizarre Admin Down change still happens.

How about posting the topology and the running-config.. All will be solved then

theodoxa

You can only have 1 SVI (e.g. "interface vlan 30") up at a time on a Layer 2 switch. If you bring up another, it will shut the previous one down. On a Layer 2 switch, an SVI is intended strictly for Management access (SSH, Telnet, etc...) to the switch, unlike on a Layer 3 switch where SVIs can function as virtual gateways for the various VLANs.

Node Man

theodoxa wrote: »

You can only have 1 SVI (e.g. "interface vlan 30") up at a time on a Layer 2 switch. If you bring up another, it will shut the previous one down. On a Layer 2 switch, an SVI is intended strictly for Management access (SSH, Telnet, etc...) to the switch, unlike on a Layer 3 switch where SVIs can function as virtual gateways for the various VLANs.

Thanks, how does this affect running ROAS on a 2950?

tomtom1

You can't. You need a L3 switch or connect the 2950 to a trunk port (802.1q) leading towards a router to do the ROAS.

theodoxa

Node Man wrote: »

Thanks, how does this affect running ROAS on a 2950?

It doesn't. Router on a Stick doesn't use SVIs at all.

SW1 Fa0/1 <--> R1 Fa0/0

STEP 1. Create the VLANs on the Switch

SW1(config)# vlan 10
SW1(config-vlan)# name Servers
SW1(config-vlan)# exit

SW1(config)# vlan 20
SW1(config-vlan)# name Users
SW1(config-vlan)# exit

STEP 2. Configure a Trunk (This will be connected to the Router)

SW1(config)# interface Fa0/1
SW1(config-if)# switchport trunk encapsulation dot1q
SW1(config-if)# switchport mode trunk
SW1(config-if)# switchport nonegotiate
SW1(config-if)# switchport trunk allowed vlan 10, 20
SW1(config-if)# exit

STEP 3. Configure the Access Ports

SW1(config)# interface range Fa0/13-18
SW1(config-if)# switchport access vlan 10
SW1(config-if)# switchport mode access
SW1(config-if)# switchport nonegotiate
SW1(config-if)# spanning-tree portfast
SW1(config-if)# exit

SW1(config)# interface range Fa0/19-24
SW1(config-if)# switchport access vlan 20
SW1(config-if)# switchport mode access
SW1(config-if)# switchport nonegotiate
SW1(config-if)# spanning-tree portfast
SW1(config-if)# exit

STEP 4. Configure the Physical Interface on the Router

R1(config)# interface Fa0/0
R1(config-if)# no ip address
R1(config-if)# no shutdown
R1(config-if)# exit

STEP 5. Configure the Virtual Subinterfaces on the Router (One for each VLAN)

R1(config)# interface Fa0/0.10
R1(config-if)# encapsulation dot1q 10
R1(config-if)# ip address 192.168.10.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit

R1(config)# interface Fa0/0.20
R1(config-if)# encapsulation dot1q 20
R1(config-if)# ip address 192.168.20.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit