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IP on VLAN or IP on Loopback in VLAN

Answered Question
Apr 23rd, 2012
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On a current Catalyst product Is it better to assign an IP address directly to a VLAN interface or to assign an IP address to a Loopback interface that is in a particular VLAN?  What are the benefits or pitfalls of either method?

Correct Answer by Dan-Ciprian Cicioiu about 5 years 3 months ago

Hi ,


You cannot configure the loopback interface as switchport. Also you cannot configure a SVI ( interface vlan ) as a switchport. So the solution is to configure the IPs on the interface vlan.


Dan

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glen.grant Mon, 04/23/2012 - 09:42
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  Not sure what you mean by a loopback address in a given vlan.  Generally you would have a single loopback for a given L3 device and this is used by any dynamic routing protocols like ospf or eigrp as this interface is always in a up/up state . 

kpieckiel Mon, 04/23/2012 - 09:56
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What I mean by that is creating a loopback interface and placing it in the particular VLAN as opposed to assigning the VLAN interface an IP address directly.  So, for example, let's take a Catalyst 6506.  If I'm hosting three VLANs 10-12 that need IP addresses (default routes for three different networks) I would potentially have three loopback interfaces with an IP address (one in each subnet consumed by those VLANs).  The alternative is to instead assign the VLAN interfaces the IP addresses and not mess with loopback interfaces.


So lets give an example.  Normally I just assign addresses to the VLANs thusly:


int vlan10

description Fiscal

ip address 10.10.10.1

int vlan11

description IT

ip address 10.10.11.1

int vlan12

description Maintenance

ip address 10.10.12.1



I'm asking if it's good, bad, or indifferent to use loopback interfaces instead:


int vlan10

description Fiscal

no ip address

int vlan11

description IT

no ip address

int vlan12

description Maintenance

no ip address

int lo10

switchport

switchport access vlan 10

switchport mode access

ip address 10.10.10.1

int lo11

switchport

switchport access vlan 11

switchport mode access

ip address 10.10.11.1

int lo12

switchport

switchport access vlan 12

switchport mode access

ip address 10.10.12.1

Correct Answer
Dan-Ciprian Cicioiu Mon, 04/23/2012 - 10:03
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  • Gold, 750 points or more

Hi ,


You cannot configure the loopback interface as switchport. Also you cannot configure a SVI ( interface vlan ) as a switchport. So the solution is to configure the IPs on the interface vlan.


Dan

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