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Beginner

No communication across devices in same native vlan

I have defined native vlan 10 and 20 across two access switches.Vlan 10 is defined as a native vlan. I connected a hub to one of the access switch and connected two PC's and given IP Add in same subnet as of vlan 10. The two access switches are connected to the L3 switch. Vlan 10 and Vlan 20 SVIs are defined in L3 switch and ip routing is enabled. The PC in vlan 10 connected to the acces switches are communicating but the PC connected to hub is not communicating. What is the issue? Please help. 

2 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Mentor

Re: No communication across devices in same native vlan

Hello


@SyedKhundmir wrote:

 I connected a hub to one of the access switch and connected two PC's and given IP Add in same subnet as of vlan 10. 


As the hub is unmanaged then the port on the access switch that is interconnecting with this hub needs to be in an access-port in vlan 10 for hosts in 10.0.0.x
Then add a additional link on the access switch towards the hub for hosts in 20.0.0.x for vlan 20, This also needs to be an access port in vlan 20 , You then should obtain connection for hosts on either vlan.

 

NOTE-  You dont require any trunk interface on the access switch towards the hub just access ports are sufficient 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

VIP Mentor

Re: No communication across devices in same native vlan


@SyedKhundmir wrote:

Encountered another problem!

 

Vlan 10 is communicating but Vlan 20 PC connected to the hub is not pingable from anywhere. Reason?


The hub doesn’t recognize the link to the access switch as a trunk, And as vlan 10 is the native vlan then trafffic from hosts in this subnet on the hub can reach the network but wont be allowed to reach hosts in vlan 20 on the hub becasue only unttaged traffic is seen, The solution as stated would be change the exisitng link to an access port in vlan 10 and add an adddtional access link for vlan 20 and communication will be established.

 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

17 REPLIES 17
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VIP Mentor

Re: No communication across devices in same native vlan

Hello,

 

if this is a Packet Tracer project, post it here (zip the .pkt file first, otherwise the system won't let you upload it...)

VIP Mentor

Re: No communication across devices in same native vlan

Hi
Check your gateways and subnet masks are correct

Check can vlan 10 first ping vlan 20 at SVI before checking pcs can ping , if they cant ping vlan to vlan ip address somethings wrong on L3 , if its working then somethings wrong on your hosts or default gateway settings on the switches
Beginner

Re: No communication across devices in same native vlan

I have checked pinging vlan to vlan its working. There must be something I am doing wrong. I have attached the topology in the other reply. Please help me.

 

Thank you for the reply. I am happy to get reply from the experts.

 

Beginner

Re: No communication across devices in same native vlan

Thank you for the reply.

 

The .pkt is attached. Kindly let me know where I am doing it wrong.

VIP Mentor

Re: No communication across devices in same native vlan

Hello,

 

interface FastEthernet0/24 on Switch1 needs to be configured as below:

 

interface FastEthernet0/24

switchport mode trunk

switchport trunk native vlan 10

 

Find attached the revised, working project file...

Beginner

Re: No communication across devices in same native vlan

I needed to edit my previous reply so sorry for that. After applying those commands I am only able to ping to vlan 10 IP on same switch but I cannot ping across the switch to other switch. I can ping from 10.0.0.3 to 10.0.0.2 and 10.0.0.4 but not to 10.0.0.1 and default gateway 10.0.0.254. Sadly I cannot open your .pkt file. 

 

Sorry to trouble you. I might be doing some silly mistake but I am sure I wil get help here.

 

Thank you for your reply.

VIP Mentor

Re: No communication across devices in same native vlan

Hello,

 

make sure the trunk ports on Switch1 look like below. It takes a while for the links to come up.

 

interface FastEthernet0/21
switchport trunk native vlan 10
switchport mode trunk
!
interface FastEthernet0/22
switchport trunk native vlan 10
switchport mode trunk
!
interface FastEthernet0/23
!
interface FastEthernet0/24
switchport trunk native vlan 10
switchport mode trunk

 

The project was saved in version 7.3.0, try and install that version.

Beginner

Re: No communication across devices in same native vlan

Your help is much much appreciated.

I did exactly as what you said and now each PC is pingable to one and another.

As hub don't understand vlan tags, I assumed that we do not need do define SW1 f0/24 as trunk link as it is connected to a hub. Now I realized that the communication is happening between the vlans and across the switches and traffic to-and-from the other switches is coming as tagged until port f0/24 so that's why we mandatory need to define that port a trunk port. Am I right?

 

Once again, thank you for your help. God bless :-)

Beginner

Re: No communication across devices in same native vlan

Encountered another problem!

 

Vlan 10 is communicating but Vlan 20 PC connected to the hub is not pingable from anywhere. Reason?

VIP Mentor

Re: No communication across devices in same native vlan


@SyedKhundmir wrote:

Encountered another problem!

 

Vlan 10 is communicating but Vlan 20 PC connected to the hub is not pingable from anywhere. Reason?


The hub doesn’t recognize the link to the access switch as a trunk, And as vlan 10 is the native vlan then trafffic from hosts in this subnet on the hub can reach the network but wont be allowed to reach hosts in vlan 20 on the hub becasue only unttaged traffic is seen, The solution as stated would be change the exisitng link to an access port in vlan 10 and add an adddtional access link for vlan 20 and communication will be established.

 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

Beginner

Re: No communication across devices in same native vlan

Bang on! Thank you for your help and time. You are amazing.

VIP Mentor

Re: No communication across devices in same native vlan

Paul's explanation is right on the money. The hub doesn't understand the Vlan tagging, so you either have to use a trunk with one of the Vlans (10 or 20) set as the native Vlan, or use an access port in Vlan 10 or 20. But either way, there is no inter-Vlan communication between the hosts on the hub, so hosts in different Vlans will not be able to communicate when connected to the same hub. What is the requirement for the network/project ? Why not simply replace the hub with a switch ?

Beginner

Re: No communication across devices in same native vlan

Yes, he is right.

 

Actually this is our network project and our instructor asked us to use switches and hubs, do trunking, native vlan and normal vlan routing and present various scenarios. I created this one and had few doubts.

 

Thank you for your time and replies.

VIP Mentor

Re: No communication across devices in same native vlan

If you need to use hubs, connect just the hosts on the 10.0.0.0 network to the hub(s) and the hosts in the 20.0.0.0 network directly to the switch. That way, you still meet the requirements your instructor has given you...

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