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Beginner

Creating a layer 2 network for migration

Please refer to this answered topic for more information: https://supportforums.cisco.com/discussion/13159756/migrating-seperate-private-network-without-changing-ips-devices

I'm trying to create a layer 2 vlan for scanners on a 192.x.x.x range to migrate to a separate network on a 10.x.x.x range.

I always thought that layer 2 vlans will accept any IP range.  As long as the vlan is trunked from top to bottom, I should be able to hard code two laptops with 192.x.x.x addresses, and they should be able to ping each other. Anything on this new VLAN should be able to communicate with each other, no matter what the IP range.  Correct, or am I way off here?

14 REPLIES 14
VIP Expert

Anything on this new VLAN

Anything on this new VLAN should be able to communicate with each other, no matter what the IP range.  Correct, or am I way off here?

Correct.  You can create a vlan and assign an IP segment to it.  For example vlan 20 with IP segment 192.168.20.0/24, vlan 30, IP segment 192.168.30.0/24 and so on. As long as the devices are in the same vlan, there is no need for routing.  If you want to communicate between vlans, than you need a router or a multi-layer switch.

HTH

Beginner

This is not an interface vlan

This is not an interface vlan though.  It is layer 2 only.  So for example:

!
vlan 22
 name Test-VLAN-22
!

The vlan is setup as switchport access vlan 22 on the device port on the switch.

Shouldn't this still work and the vlan will pick-up any IP info configured on the device?

VIP Expert

Yes, this should work fine. 

Yes, this should work fine.  So, for vlan 22 your subnet maybe 192.168.22.0/24.  You can have DHCP assign IP address to devices or simply use static IPs.

HTH

Beginner

Ok, that is what I thought..

Ok, that is what I thought.. But for some reason the static IP devices are not communicating.  They send packets, but do not receive, and cannot ping each other. They do not have firewalls enabled or anything like that.

Hall of Fame Master

It might be helpful if we had

It might be helpful if we had some information from the original poster about how this is set up. What IP address and what subnet mask are configured on the various hosts in the network. We have said that any two hosts in the same vlan should be able to communicate directly with each other without needing a router or any other device. And from the perspective of the switch that is true. From the perspective of the host that might or might not be true. If the hosts will send arp requests for each other and respond to arp requests from the other then they would certainly be able to communicate. So the question becomes will these hosts arp for each other? What if one or both host believe that the other host is in a different subnet. Some versions of OS will only send arp requests for addresses that it believes are in the same subnet and for addresses outside of the subnet will attempt to use its default gateway. So we may need to know if these hosts believe that they are in a common subnet or not.

It might be helpful to see the output of arp -a (or similar command if the host is not Windows) to see what the host has in its arp table.

HTH

Rick

Beginner

Hi Rick - Thanks for the

Hi Rick - Thanks for the reply.  The two hosts I have setup to test have the IP addresses of 192.168.6.186 and 192.168.6.200.  Both have subnet masks of 255.255.255.0

This is the output I receive when I do an arp -a from one of the hosts:

Interface: 192.168.6.186 --- 0xb

  Internet Address      Physical Address      Type

  192.168.6.255         ff-ff-ff-ff-ff-ff     static

  224.0.0.2             01-00-5e-00-00-02     static

  224.0.0.22            01-00-5e-00-00-16     static

  224.0.0.251           01-00-5e-00-00-fb     static

  224.0.0.252           01-00-5e-00-00-fc     static

  239.255.255.250       01-00-5e-7f-ff-fa     static

  255.255.255.255       ff-ff-ff-ff-ff-ff     static

Hall of Fame Master

Thanks for the additional

Thanks for the additional information. These two host addresses should certainly attempt to arp for each other and there should be no need for any default gateway for them to communicate. So that is one potential problem that is eliminated.

The arp output shows that the two PC are not communicating with each other. So we need to understand better how they are connected. Is this on a single switch or on multiple switches? Would you post the output of these commands from each switch

show vlan

show interface trunk

show cdp neighbor

HTH

Rick

Beginner

Hi Rick thanks again.  For

Hi Rick thanks again.  For this test, the two PC's are on the same switch. Here is the requested output (truncated to only include relevant information)

show vlan:

22  Test-vlan-22                     active    Gi1/6, Gi1/7

show int trunk:

Port        Mode             Encapsulation  Status        Native vlan
Te3/1       on               802.1q         trunking      1

Port        Vlans allowed on trunk
Te3/1       22,100,105,108

Port        Vlans allowed and active in management domain
Te3/1       22,100,105,108

Port        Vlans in spanning tree forwarding state and not pruned
Te3/1       22,100,105,108

sho cdp nei:
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
CoreSwitch1       Ten 3/1           125             R S I  WS-C4510R Ten 9/5

Hall of Fame Master

Thanks for the information.

Thanks for the information. Having it on a single switch keeps it simple. The output of show vlan seems to show that the two hosts should have local communication. Would you post the output of show mac address-table from the switch?

HTH

Rick

Beginner

The ports are seeing the mac

The ports are seeing the mac addresses of the hosts:

sho mac address-table
Unicast Entries
 vlan     mac address     type        protocols               port
---------+---------------+--------+---------------------+-------------------------
 22      28f1.0e02.314f   dynamic ip,ipx,assigned,other GigabitEthernet1/6         
 22      f01f.af43.8d9e   dynamic ip,ipx,assigned,other GigabitEthernet1/7 


Multicast Entries
 vlan     mac address     type    ports
---------+---------------+-------+--------------------------------------------

  22      ffff.ffff.ffff   system Gi1/6,Gi1/7,Te3/1

Hall of Fame Master

Yes the switch is seeing the

Yes the switch is seeing the MAC of both hosts. Please attempt to ping host to host and then do arp -a on both and post the output.

HTH

Rick

Beginner

From 192.168.6.186 host to

From 192.168.6.186 host to 192.168.6.200:

 

ping 192.168.6.200

 

Pinging 192.168.6.200 with 32 bytes of data:

Request timed out.

Request timed out.

Request timed out.

Request timed out.

 

Ping statistics for 192.168.6.200:

    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss

 

arp -a

 

Interface: 192.168.6.186 --- 0xb

  Internet Address      Physical Address      Type

  192.168.6.200         f0-1f-af-43-8d-9e     dynamic

  192.168.6.255         ff-ff-ff-ff-ff-ff     static

  224.0.0.2             01-00-5e-00-00-02     static

  224.0.0.22            01-00-5e-00-00-16     static

  224.0.0.251           01-00-5e-00-00-fb     static

  224.0.0.252           01-00-5e-00-00-fc     static

  239.255.255.250       01-00-5e-7f-ff-fa     static

  255.255.255.255       ff-ff-ff-ff-ff-ff     static

From 192.168.6.200 to 192.168.6.186:

ping 192.168.6.186

Pinging 192.168.6.186 with 32 bytes of data:
Reply from 192.168.6.200: Destination host unreachable.
Reply from 192.168.6.200: Destination host unreachable.
Reply from 192.168.6.200: Destination host unreachable.
Reply from 192.168.6.200: Destination host unreachable.

Ping statistics for 192.168.6.186:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

arp -a

Interface: 192.168.6.200 --- 0xb
  Internet Address      Physical Address      Type
  192.168.6.255         ff-ff-ff-ff-ff-ff     static
  224.0.0.22            01-00-5e-00-00-16     static
  224.0.0.252           01-00-5e-00-00-fc     static
  255.255.255.255       ff-ff-ff-ff-ff-ff     static

Hall of Fame Master

Thanks for doing this test.

Thanks for doing this test. It looks like we are making some progress, though there are still some issues that I do not understand.

On the positive side we see that at least in terms of ARP that we have successful communication between the hosts. In this output

arp -a 

Interface: 192.168.6.186 --- 0xb

  Internet Address      Physical Address      Type

  192.168.6.200         f0-1f-af-43-8d-9e     dynamic

we see clearly that 6.186 and 6.200 have communicated. The ping was not successful but we did have successful communication between the hosts for ARP. So it suggests that there is some policy (or some device firewall) that is not permitting ping.

But we have puzzling results in this output

arp -a
Interface: 192.168.6.200 --- 0xb
  Internet Address      Physical Address      Type
  192.168.6.255         ff-ff-ff-ff-ff-ff     static

So 6.200 attempted arp but it was not successful. I find it puzzling that between a pair of hosts that arp is successful in one direction but fails in the other direction. I am not clear what the issue is but believe that it is much more likely an issue with the hosts and not an issue in the switch configuration.

HTH

Rick

Highlighted
Beginner

Hi Rick - Thanks for the

Hi Rick - Thanks for the reply.  I think you're right, it has to be something on the host side of things.  Maybe a Windows 7 issue, hard to tell for sure.  But either way, I setup the exact configuration in Packet Tracer and it works fine.  I actually trust Packet Tracer to simulate the end devices more than I do a Windows PC. :)

Thanks again.

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