Loopback0 CAT3550

[michael.m.williams]

I am trying to set up a loopback0 port on my 3550-24. I want to use it as my management port. It lets me configure the loop back.

interface Loopback0

ip address 10.244.244.24 255.255.255.255

ip broadcast-address 10.244.244.255

But I can never ping it from my work station. I can't figure out what I am doing wrong. Can anyone help me please?

Thanks

Michael M. Williams

Network Systems Analyst

Information Technology Services

Tarleton State University

[michael.m.williams]

Rick,

Here is what i got when I typed in the static route.

Password:

network-office#config t

Enter configuration commands, one per line. End with CNTL/Z.

network-office(config)#ip route 0.0.0.0 0.0.0.0 10.244.244.24

%Invalid next hop address (it's this router)

network-office(config)#

Thanks

mike

[Richard Burts]

Mike

It may not feel like it but I think we are making progress. You say that ip routing is enabled and the most recent show ip route confirms it:

Gateway of last resort is not set

10.0.0.0/32 is subnetted, 1 subnets

C 10.244.244.24 is directly connected, Loopback0

xxx.xx.0.0/25 is subnetted, 1 subnets

C xxx.xx.21.0 is directly connected, Vlan9

network-office#

You were not getting that output before and seeing the connected interface subnets is confirmation that ip routing is enabled. This is essential to getting the loopback to work.

This output also shows what appears to be another problem.

Gateway of last resort is not set

Probably it would make sense to configure a default route using the same next hop that was specified in your default gateway command.

I am sorry that the form of the static route that I gave you produced an error. I looked at what you had tried to configure in a previous post and to correct it. I took what I thought was a specification of next hop and put it into the right place without realizing that the address was the loopback interface address. Perhaps I should not have made assumptions about what you were trying to do and should have just asked what you were trying to achieve with the static route. Once I understood that perhaps my advice would have been better.

If you take the static route that I gave you and change the next hop to be your default gateway address I believe that it should work.

ip route 0.0.0.0 0.0.0.0 xxx.xx.21.125

HTH

Rick

[michael.m.williams]

Rick,

Here is what i got

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is 165.95.21.125 to network 0.0.0.0

10.0.0.0/32 is subnetted, 1 subnets

C 10.244.244.24 is directly connected, Loopback0

xxx.xx.0.0/25 is subnetted, 1 subnets

C xxx.xx.21.0 is directly connected, Vlan9

S* 0.0.0.0/0 [1/0] via xxx.xx.21.125

Still can't ping it.

thanks

Mike

[glen.grant]

When you hook up your pc are you putting in the default gateway for the vlan you are attached to? If connected to a port in vlan 9 then your pc nic card gateway would be xxx.xx.21.113 and your netmask on your pc should be 255.255.255.128

[michael.m.williams]

Glen,

Yes, my PC is coming off a port of the switch i am trying to config loopback0 on. The IP of my PC is xxx.xx.21.60, subnet is 255.255.255.128.

thanks

mike

[Thotsaphon Lueangwattanaphong]

Mike,

PC should be configured look like this:

xxx.xx.21.60 mask 255.255.255.128 GW xxx.xx.21.113

To make sure that this pc is connecting to the port assigned to the vlan9

I want you to configure "ip routing" command in the configuration mode.I want to see "int vlan 9 up up" in the "sh ip int brief" command.

Please let us know how things work out!

Thot

[michael.m.williams]

Thot,

I did the changes you stated and I was able to ping the loopback0 Ip, but i was not able to reach any other device on the network.

I have configurted ip routing

network-office#sh ip in brief

Interface IP-Address OK? Method Status Protoc

Vlan1 unassigned YES NVRAM up up

Vlan9 xxx.xx.21.113 YES NVRAM up up

FastEthernet0/1 unassigned YES unset up up

Loopback0 10.244.244.24 YES manual up up

Thanks

Mike

[Thotsaphon Lueangwattanaphong]

Mike,

Thanks for updating the status. I want to know that this switch is a core switch(for routing networks),isn't it?

if not, then who? and what is the interface mode do you connect the core switch? trunking by using f0/1?

HTH

Thot

[michael.m.williams]

Thot,

i want to do this for all my access switches. This one is a 3550. Right now we are using the production VLAN for both data and management and I want to move awayfrom that. My Core switch already has a loopback0 port and i wanted to use the same IP range for all my other switches. From what i read Loopback0 port could do this for me, but i can't get it to work.

I use fa 0/1 on this switch as a trunk.

Thanks

mike

[Thotsaphon Lueangwattanaphong]

Mike,

Bingo! This switch has to be configured as Layer2 Switch as you did. So no "ip routing" command on it. You CANNOT use a loopback ip address for management at the Layer2 switch(in your case). you have to only pick one vlan(Active!) to do that. And configuring "ip default gateway" to point to your core-switch.

HTH

Thot

[Richard Burts]

Mike

I am not sure that I would go quite as far as Thot and say "the switch HAS to be configured as layer 2". But first we really need to know how you want your network to operate. It seems that previous to this discussion and the changes that you made in it, the network was a group of layer 2 switches which were trunked to a core which did all of the routing.

You can keep that architecture or you can choose to change it by enabling ip routing on the access switches (at least all the access switches that are layer 3 capable). Making the change from a layer 2 switch to layer 3 is a decision that should be intentionally made. I believe that we pushed you into this change because we made assumptions about what you were trying to accomplish and without understanding the existing environment.

Thot MAY be right that you should go back to the layer 2 operation and remove ip routing from this switch. You can still accomplish your basic objective which seems to be that you want management to be in a separate VLAN from production data. So you would configure some VLAN for management. That is the interface vlan x that you would configure with an IP address.

And Thot certainly IS right that if you go back to layer 2 operation that you can not use a loopback interface.

HTH

Rick

[michael.m.williams]

Rick,

Ok, thanks I will use a seperate VLAN for management. I didn't want to change to entire architecture of my network to make it work. I was trying to find an out of bound solution to manage my switches. Maybe i went about all wrong. So the best way is just to creat a seperat VLAN to manage my switches? Or is there another way? i have 100+ switch that all have different management IP in multiply production VLAN. I want to make things easier.

Thanks

mike

Mike

[michael.m.williams]

Thot,

That would explains why it doesn't work. Cisco has documentation that loopback0 would work with 3550. So even after I enable routing it will not work?

thanks

mike

[Richard Burts]

Mike

Interface loopback 0 COULD work - if you make the right set of changes. But as I said in a previous post these changes would be a significant change in the architecture of your network.

You asked a question about how to get interface loopback 0 to work. And we have been very energetic in trying to make it work. Perhaps we should have spent a little more time trying to figure out what the fundamental objective was. There is a strategy to get management interfaces on the switch separate from the data VLAN when operating as layer 2 switch and there is a strategy to get management interface that is separate when operating as layer 3 switch. When you can tell us which strategy you prefer we can help you implement it.

If you go the layer 3 strategy with a loopback interface then you will need to make sure that your switch has routing information about how to reach the various remote destinations. And you need to make sure that other devices in your network have information about how to get ot the address of your loopback interface. Probably that is a bunch of static routes or it is a dynamic routing protocol.

HTH

Rick

[michael.m.williams]

Rick,

After you folks made me wiser on this I believe the best way to do it is via layer 2. Adding multiple static route will become time consuming and complicated. I am trying to make things easier.

Any suggestions?

Thanks

mike