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Zach8585
Beginner

inter-vlan with VLSM and Router on a stick not working

Studying for my CCNA, including a cisco lab with one switch and one router.  Right now it's not attached to the internet (via cable modem), that will be later down the road.

 

Here's a brief overview of my current set up:

 

on the switch (3560 8 ports):

three vlans:

1 - native; 192.168.1.253 255.255.255.252

20 - 192.168.1.66 255.255.255.240

30 - 192.168.1.2 255.255.255.192

Gi0/1 set for dot1q trunking to router's Gi0/0 interface

 

on the router (2800 series):

Gi0/0 - 192.168.1.254 255.255.255.252

Gi0/0.20 - 192.168.1.65 255.255.255.240

Gi0/0.30 - 192.168.1.1 255.255.255.192

 

DHCP is set up on router as following:

 

VLAN20 scope

- Network 192.168.1.64 255.255.255.240

- Default-router 192.168.1.65

 

VLAN30 scope

- Network 192.168.1.0 255.255.255.192

- default-router 192.168.1.1

 

On the switch, I have FA0/1 and FA0/2 set to VLAN 20, and FA0/3 set to VLAN 30.

 

When I have two separate computers plugged into FA0/1 and FA0/2, they can see each other no problem, ping, file share, etc.

 

However, when I put one of the two computers onto FA0/3, they can't see each other, and I've verified that DHCP is working correctly on both VLANS.  Yet, they can ping the switch's VLAN interface and router-sub interfaces of both VLANS.  In other words, they are crossing over the VLAN/Subnet "borders".  So I don't get what is the problem when inter-vlan routing is obviously happening at layer 3 (Router) when I'm able to ping the switch's interface and router's subinterface across the vlan and subnets.

 

Anyone have any idea what I'm missing?  Show IP Route does show the networks via the correct sub-interface.  both switch and router can ping all six interface ip addresses, both computers can ping all six.

 

Any help would be appreciated, especially since I'm planning to take my CCNA test by the end of July.

 

Final note: when I do this exact set up in cisco packet tracer, it works fine. 

 

Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
johnd2310
Collaborator

Hi,

 

Post your router and switch config

 

Thanks

John

**Please rate posts you find helpful**

View solution in original post

2 REPLIES 2
johnd2310
Collaborator

Hi,

 

Post your router and switch config

 

Thanks

John

**Please rate posts you find helpful**

View solution in original post

Hi John,

 

I had inadvertently (but thankfully) discovered the issue.  My server lab (from my MCSA days which I obtained that cert two months ago) has several virtual interfaces with its three physical NIC interfaces (One motherboard NIC and one NIC with two interfaces).  When I would do testing with the cisco lab, I would turn off the internet-facing NIC card, which would also turn off the virtual external card that is tied to it for my many Virtual machines I have in Hyper-V.

 

For some reason, that external virtual interface was causing the issue.  I figured out how to turn off only the physical card and leave the virtual card on, which allowed me to pin across the border.

 

What's confusing is how it still allowed me to ping all of the switch and router interface IPs regardless.  But I'm not too worried about that for now as it isn't related to Cisco.

 

I ended up just bringing up another laptop and attaching that to a different VLAN from my main laptop, and I was able to ping both ways.  I wish I had discovered this before completely resetting both the router and switch thinking I had a configuration issue :(

 

Anyways, thanks for your response and willingness to help out.  I'll definitely be back to this forum if I have any further issues or questions.

 

Thanks,

Zach