Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Impact of IP subnet assignment overlap in VLAN's and throughout switches infrastructure

Hi,

I need to move PC's from the default VLAN 1 into another VLAN 5.  I want to also reassign the IP's from VLAN 1 to VLAN 5 on all devices within the infrastructure.  Here is the current setup of 2 switches.

Cisco 3750:

Interface VLAN 1

 IP address 10.0.252.1 255.255.252.0

Interface VLAN5

 No IP address

Interface VLAN 100

 IP address 10.0.251.1 255.255.255.0

 

Cisco 2960

Interface VLAN 1

 IP address 10.0.252.2 255.255.252.0

Interface VLAN5

 No IP address

Interface VLAN 100

 IP address 10.0.251.2 255.255.255.0

 

How would I go about removing the IP from VLAN1 and reassigning to VLAN5?  Using a PC located in VLAN 100 I know that if try and assign the same IP from VLAN 1 to VLAN5 without removing the VLAN1 IP first I get a conflict error, which is what I expect.  However I was thinking that using the PC on VLAN 100 I could remove the IP address from VLAN1 and assign to VLAN5, then hop onto the next switch and do the same.  There will be approx. 20 switches I need to make this change on.  My question is do I have to hop onto all 20 switches first(using PC in VLAN100) and remove the VLAN1 IP address before reassigning any of the addresses on VLAN5.  The reason I ask is that if I didn't there would be for a short time while I hop onto all 20 switches where an overlap with the IP addresses and subnet would be on VLAN1 and VLAN5. 

Would I still get the error of conflict if for example I performed the following on the Cisco 3750 before I made the same change on the 2960:

Cisco 3750:

Interface VLAN 1

 No IP address

Interface VLAN5

IP address 10.0.252.1 255.255.252.0

Interface VLAN 100

 IP address 10.0.251.1 255.255.255.0

 

Cisco 2960

Interface VLAN 1

 IP address 10.0.252.2 255.255.252.0

Interface VLAN5

 No IP address

Interface VLAN 100

 IP address 10.0.251.2 255.255.255.0

 

If I didn't get the conflict error when reconfiguring the 3750 what impact would it have on the network if 2 VLAN's temporarily shared an overlapping subnet?  Would there be a routing problem with devices attached to the other VLAN's like VLAN 100 for example.

 

Any help appreciated

  • LAN Switching and Routing
Everyone's tags (1)
1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Hi Craig,Hosts connected to

Hi Craig,

Hosts connected to SVI VLAN100 will not lose connectivity as nothing changes there.

However, the network will be down for hosts connected to SVIs VLAN1 and VLAN5.

A good practice would be removing all the IP addressing and configure it thereafter.

 

Kind regards,

- Ed

 

2 REPLIES
Cisco Employee

Hi Craig,Hosts connected to

Hi Craig,

Hosts connected to SVI VLAN100 will not lose connectivity as nothing changes there.

However, the network will be down for hosts connected to SVIs VLAN1 and VLAN5.

A good practice would be removing all the IP addressing and configure it thereafter.

 

Kind regards,

- Ed

 

New Member

Thanks for the reply Ed.Could

Thanks for the reply Ed.

Could I ask at what point the clients would lose connectivity in VLAN1 as their default IP address is actually that of the 3750?  If I removed the IP address from the VLAN1 switch on the 2960 would the clients still have connectivity until the IP address is removed from the 3750?

Thanks

378
Views
0
Helpful
2
Replies