Ok, I tried to add a vlan to the Loopback interface but didn't have any success.  I also orginally tried to give the loopback an address with the management network and this was also a bust.  How do I accomplish this?  While the topic heading is Loopback routing, mainly I'm just looking for a way to configure the switches so that a network management workstation can hit loopback interfaces across a network.

charles.e.davis@baesystems.com
Ok, I tried to add a vlan to the Loopback interface but didn't have any success.  I also orginally tried to give the loopback an address with the management network and this was also a bust.  How do I accomplish this?  While the topic heading is Loopback routing, mainly I'm just looking for a way to configure the switches so that a network management workstation can hit loopback interfaces across a network.

It does depend on how your L3 switches are setup. Are they all routing and are they exchaging routes between each other. Because if they are not then it work. Bear in mind each loopback interface is a L3 interface. So let say your management workstations is connected via a L2 switch to a L3 switch that routes for the 10.255.255.0/25 vlan.

Now for the management workstation to be able to get to any loopback that L3 switch needs a route for each loopback. So all the other L3 switches with loopbacks would need to have advertised their loopback address. Now you can't do this with a vlan as such.

So it really depends on how the switches with loopbacks are advertising that loopback address. It may be that only a pair of your L3 switches are responsible for inter-vlan routing and the rest are connected via L2 trunks in which case you could be looking at a lot of static routes for the loopbacks on the L3 pair that are doing the inter-vlan routing.

It also depends on how the L3 switches are interconnected ie. via L2 trunks or L3 routed links.

Perhaps you could provide some more details on how everything is connected up and how the routing between the L3 switches is setup ?

Jon

Currently, we are using the layer 3 switches as the primary and secondary default gateways for inter-vlan routing.  We are running OSPF between the switches to allow for route switching.  The network management ws is directly connected to the primary layer 3 switch.  Considering that the loopback interface is a layer 3 interface, how would you ever route traffic to it across a network since it can't be directly tied to an interface.  Of can I advertise for that network 10.255.255.128/25 so that the loopbacks will respond.  I really appreciate your help on this, I know it is a saturday.

I forgot to mention, I do have a management vlan 10.255.255.0/25 that is routed through my trunks.  I had hoped to just put leave the subnet alone orginally, 10.255.255.0/24, and put the loopbacks on that vlan.  But there was no luck with that.

charles.e.davis@baesystems.com
I forgot to mention, I do have a management vlan 10.255.255.0/25 that is routed through my trunks.  I had hoped to just put leave the subnet alone orginally, 10.255.255.0/24, and put the loopbacks on that vlan.  But there was no luck with that.

That's the problem with using loopbacks when you have L2 trunks connecting your switches.

Lets say you have 5 L3 switches sw1 -> sw5.

sw1 is responsible for inter-vlan routing and has a L3 SVI for the management vlan with an address 10.255.255.1/25.

sw2 -> sw5 each have a L3 SVI for the management vlan and use IPs 10.255.255.2. -> 5 respectively.

If you now want to add a loopback to each switch ie. sw2 -> sw5 using 10.255.255.129 -> 132 you would need to add these static routes to sw1

ip route 10.255.255.129 255.255.255.255 10.255.255.2  <-- sw2

ip route 10.255.255.130 255.255.255.255 10.255.255.3  <-- sw3

etc...

loopbacks work well when each device with a loopback is routing and exchanging routes with all other L3 devices.

Jon

Ok, so since I'm using multiple layer 2 switches (2960Gs) with only 2 layer 3 switches (3750G), then I need to put a static route on both 3750s for each switch that I have a loopback address on, which will be all of them.  Am I correct or did I not understand you?

Ok that worked perfectly.  Thanks for your help.