Loopback interface on catalyset switches

Hello,
I need to know if I can configure loopback interfaces on L2 switches (2950) and if yes , in which IOS
Thanks
Moamen

Hello,
for admin, I need to create loopback interface and use it as the admin IP to reach the switch
I know that the admin ip configured under interface vlan1
but I'm asking because I have a switch that has the int loopback in his menu when using
conf t# int ?
I can found loopback , but I can't configured it
switch(config)#interface ?
Async Async interface
BVI Bridge-Group Virtual Interface
Dialer Dialer interface
FastEthernet FastEthernet IEEE 802.3
Group-Async Async Group interface
Lex Lex interface
Loopback Loopback interface<<<<<
Multilink Multilink-group interface
Null Null interface
Port-channel Ethernet Channel of interfaces
Tunnel Tunnel interface
Virtual-Template Virtual Template interface
Virtual-TokenRing Virtual TokenRing
Vlan Catalyst Vlans
range interface range command
System image file is "flash:c2950-i6q4l2-mz.121-22.EA3"
but when I'm trying to configure it the switch refused
Thanks & BR
Moamen

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Baseline template - look for specific loopback interface when specifying "ip tftp source-interface"

Hello all
I'm new to regex and I'm trying to make a baseline template, that will check our network devices for our required basic configuration.
What I'm trying to do is to make a template that will look for either a loopback0 or loopback1 interface.
If eíther one is found (the loopback interfaces will not be there at the same time) it must apply the following command:
ip tftp source-interface loopback0 (or loopback1)
Is it even possible to make an if-then statement using regex?
Thank you in advance.
Best regards
Jesper Ross Petersen
Message was edited by: Jesper Ross Petersen

Yes, this can be done
#Go to the tcl shell of the device.
C1811#tclsh
C1811(tcl)#
#copy and paste this at the tcl prompt.
proc intf {} {
set runningcfg [exec show run | inc ^interface Loopback]
foreach line [split $runningcfg \n] {
if {[regexp {interface (Loopback[0-1])} $line -> interface] } {
ios_config "ip tftp source-interface $interface"
return "ip tftp source-interface $interface"
# now type the name of the proc (intf) at the tcl prompt.
C1811(tcl)#intf
# If loopback0 or 1 is present the tftp source interface is added to the running config.
ip tftp source-interface Loopback0
C1811(tcl)#

Missing loopback interface and modules, and isofs mounting [SOLVED!]

In my new archlinux istallation, isofs and loopback facilities are not present and when installed by hand do not seem to work. [See FINAL SOLUTION below. Thanks for the suggestions I got].
Now, I was under the impression that such facilities should be automatically available at the end of a normal installation.
For instance, in an installation I made last fall, I can mount .iso filesystem through the loopback interface with no problems (and that even without using -t, with just 'mount image.iso /mnt/iso'). In that installation, lsmod shows the modules
loop 18526 2
isofs 32946 1
(also, a module isofs is present in /lib/modules, though I cannot find a loop module there)
and eight loopback devices are available as /dev/loop0 ... /dev/loop7
On the other hand, in the new installation no /dev/loop devices are present, and no loop and isofs modules show up either
as installed (as reported by lsmod) or at least in the libraries. Has something changed recently? Do I need to install a package that will set up my installation for loopack mounting and mounting of .iso filesystems?
INTERIM SOLUTION
I mentioned above that in my older Linux box, on an Arch Linux installed months ago but not upgraded for many weeks, I had loopback devices running and isofs and loop modules installed, and all working well by itself. Today I did an upgrade, and noticed that it came with a new kernel (3.3?), probably the same I had on the new machine. So I rebooted after that---and found the exact problem as on the new machine: /dev/loop* missing, no modules isofs or loop appearing in lsmod. So I installed by hand a loopback interface, with 'mknod /dev/loop0 b 7 0'. Then I made sure I had the isofs package installed, and installed the isofs module with modprob; this time isofs showed on lsmod, but loop didn't yet. Finally I mounted a data DVD (note that the incantation -t iso9660 is no longer necessary), and as a last thing I mounted an .iso file; both worked. Only after this did a module loop show up in lsmod.
So probably something subtle changed in the dependencies between installed packages, installed modules, and installed loopback devices, so that something is out of sync and has to be nursed manually. Better experts than I may throw
some light on this problem and hopefully fix it.
FINAL AND SATISFACTORY SOLUTION
Whatever may have happened before, the following works like a charm:
I upgrade Arch; it installs 3.3.1-1-ARCH as a kernel in /boot.
I reboot to let the new kernel "take".
No loop0,...,loop7 devices show up in /dev; no isofs or loop show up with lsmod; isofs (but no loop) present in /lib/modules
I do 'mount /dev/sr0 /iso' (NOTE: no -t iso9660' option) with a CD in the sr0 drive; the CD filesystem shows up in /iso.
After this, isofs shows up in 'lsmod|grep isofs', but no loop device yet.
I unmount /iso and do 'mount ~tt/ markov.iso /iso' (NOTE: no -t iso9660' option); the markov filesystem shows up in /iso.
After this, loop0,...,loop7 devices show up in /dev, and a loop module (wherever that camefrom) appears in lsmod.
In other words, everything required for isofs automounts as necessary and remains mounted until new reboot.
The '-t iso9660' option is not necessary. As noted by an other Arch post, this option may be detrimental and might have been the culprit; this is an issue I will explore on the next reboot.
Last edited by rugantino (2012-04-11 20:11:55)

When /etc/rc.sysinit is invoked during the bootprocess; it should automatically start a loopback interface (unless you've specifically disabled it in /etc/rc.d/network or so).
Check your logs to see if your find any related errors.

Crypto Map on Loopback interface or Physical Interface

Dear All,
When we try to apply the crypto map on any physical interface or the loopback interface on WS-6506-E, it is showing the error. But the same i could apply on VLAN interface. Can anyone explain me what is the issue..?
6506(config)#interface loopback 3
6506(config-if)#crypto map XXXX
ERROR: Crypto Map configuration is not supported on the given interface
Any hardware limitation?

This was proven to break CEF in the past and is a bad design choice by default.
Newer release do not allow you to configure this.
If you're curious if it will work for you check releases prior to 15.x.
M.

Benefit of loopback interface

why do we use a loopback, is it just for when we are using routing protocols, and if say a router has 2 interfaces, the loopback can be reached from both ?

Hello Carl,
Loopback interfaces are indeed often used with routing protocols as ospf, bgp, eigrp.
The advantage is that loopback interfaces are always up, because they are virtual. If they can be reach depends ofcourse on your routing protocol.
Ik you have for example a router with 3 physical interfaces all connected and your routing is configured correctly then the remote side can always reach your loopback till all paths (physical) are down.
But there are a lot more reasons to use loopbacks, but i think this one is the most important one.

Using Ciscoworks to update netmask on mgmt interface for multiple switches

Is it possible to user Ciscoworks LMS 3.2 to update the netmask for a management interface on multiple switches? For example, say I have a 3750 access switch management network, 172.28.185.0/27 (default gateway 172.28.185.1) that we're resizing to a /26. Is there a simple way to update just the netmask for the management interface on those devices using Netconfig?
-David

Unfortunately not. You could use Netconfig or even baseline compliance for this, but since you need to know each interface's IP, that means you'd have to create parameterized templates. Therefore, you would have to create a template "answer" file for each device in this subnet which had their IP address for the interface in question.
Baseline compliance might be a little easier with a template like:
Commandlet : CheckIP
IsPrereq : Yes
Submode : interface [#.*Ethernet.*#]
+ ip address [#172.58.185.\d+#] 255.255.255.224
Commandlet : ReplaceIP
Parent : CheckIP
+ ip address [IP] 255.255.255.192
You would still need to provide a value for [IP] for each device when performing a deployment.

Adding Loopback interface for branch routers

Hi,
I have several branch routers that i want to add a loopback interface for managament purposes. I am currently using ospf as my routing protocol.
Will the rotuer-id be updated accordingly and will there be any effect on my ospf routing?
Thanks.

Hi,
No, the router id will not change unless you clear the OSPF process. So, this will cause an outage to your environment and should be done during a maintenance window.
from the ospf document:
OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces. If there are no loopback interfaces present, the highest IP address in the router is chosen. The OSPF cannot be directed to use any particular interface. Once the router ID is elected, it does not change unless the OSPF process restarts or the router is reloaded.
http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/23862-duplicate-router-id-ospf.html
HTH

OSPF and loopback interface

Hello,
When you set a loopback interface port, do you use the same ip address as the interface configured for the area number? Example, if the interface is 192.168.0.1, will your loopback ip address be 192.168.0.1?
Do you increment the ip address for example: 192.168.0.2
Thank you,

Jason
I do not understand whether your question is asking how you configure a loopback interface or whether you are asking how you configure OSPF to process on the loopback interface.
A loopback interface is a virtual interface on a router. You assign an IP address to the loopback interface much as you would assign an address on a physical interface. The subnet mask for the loopback interface can be a normal subnet mask or it could be a host specific /32 mask (255.255.255.255). What mask to use depends on how your network is designed.
Once you have assigned an IP address on the loopback interface if you want to have OSPF include the interface then you would need a network statement under router ospf that would include the loopback interface address. If your loopback interface were assigned address 172.16.1.10 then any of these network statements could work:
network 172.16.1.10 0.0.0.0 area 10
network 172.16.1.0 0.0.0.31 area 10
network 172.16.0.0 0.0.255.255 area 10
If this does not explain what you want then perhaps you can clarify your question.
HTH
Rick

Loopback interface as dial peer?

Can a loopback interface be specified in the session target command when configuring dial peers for FXS ports? Currently using a physical address and have an application that needs to specify a logical address. Will try in lab environment. Just wondering if anyone has done this?

Yes, you can.
Be sure to put h323-gateway voip interface
and h323-gateway voip bind srcaddr under the loppback interface.
This is actually the preferred method.

Loopback Interface

What is the purpose of the loopback interface?

Sherman
A loopback interface is a virtual interface that can be configured on a router. When we say it is a virtual interface this means that it logically exists but it does not exist physically (there is no physical interface and no cable to plug into it). One important aspect of the loopback interface is that it removes physical dependencies - you can not unplug a cable and have the interface go down (unless the cable was the power cable for the router).
The loopback interface can have many uses. Some routing protocols have the concept of a routerID and we frequently want a loopback interface address to be the RID (because it is more stable than any physical interface). We frequently want to use a loopback interface addresses for management purposes. We may want to source our SNMP messages from the loopback. If we want to ping an interface on the router to determine whether the router is up or not it is good to ping the loopback interface. If you want to telnet to the router you do not have to be concerned whether you are accessing it by its serial interface, its Ethernet interface, or any other interface if you telnet to the loopback interface address. If you are using AAA and an ACS server for authentication it is good to source the authentication packets using the loopback interface. Some protocols need to specify peer addresses (BGP, and GRE tunnels and IPSec are examples that come to mind) and it may be advantageous to use the loopback interface address as the peer address.
There are more uses for loopback interfaces but this gets the discussion started.
HTH
Rick

DMVPN using loopback interface vs. physical interface

In a DMVPN,what´s the difference between using a loopback interface as a tunnel source instead of a physical interface?

It will work for a static one to one nat. PAT doesnt play well with GRE because ports dont exist in GRE (not sure if NAT traversal can help here like it does with ISAKMP - it works on spokes) You also need to make sure that the loopback is set to work with the crypto profile. Joe is right, the address it terminates on is best to be Public address space that you own, that is multihomed - if this is a hub.

Configure interface vlan on switch 3524 XL

Hi all,
I have an old switch C3524 running image "C3500XL-c3h2s-mz-120.5.2-xu". I had successfully created vlan 120 but when I config "interface vlan 120" as follows:
swicth # conf t
switch(config-subif)#interface vlan 120
switch(config-subif)#ip address 172.10.10.1 255.255.255.0
switch(config-subif)#no shut
then show run does not see this interface. Show vlan indicates vlan 120 is active.
Please help. thank you.

you're right. I just shut down interface vlan 10 (interface vlan 1 is down already) then interface vlan 120 comes up. Question is: if I need to configure several ports: some in vlan 10 and some in vlan 120 then should I have interface vlan 10 up too ?
Thank you very much.

Loopback interface performance...

Hi all,
I've got an application that runs in a Solaris box. During application cycles, it needs to make internal call to itself (web-Services based architecture) and until now they were using the Internet IP of the box (hme0 interface).
Would it not be better to use the loopback interface (lo0) for internal connections instead of using the normal internet interface (hme0) ?
Is the loopback interface more suitable for this purpose ? is it scalable enough ?
our ifconfig as follows :
hme0: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 1
inet 192.168.0.6 netmask ffffff00 broadcast 192.168.0.255
hme2: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
inet 129.157.66.18 netmask ffff0000 broadcast 129.157.255.255
hme2:1: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2
inet 129.157.66.28 netmask ffff0000 broadcast 129.157.255.255
lo0: flags=1000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv4> mtu 8232 index 3
inet 127.0.0.1 netmask ff000000
Thanks in advance.
Nicolas

The loopback interface address of 127.0.0.1 seems to work well:
sd-6:/tmp
root:=> mkfile 100m test
sd-6:/tmp
root:=> ftp 127.0.0.1
Connected to 127.0.0.1.
220 sd-6 FTP server ready.
Name (127.0.0.1:root): root
331 Password required for root.
Password:
230-Please read the file README.pdf
230- it was last modified on Wed Dec 15 15:26:58 2004 - 39 days ago
230 User root logged in.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> bin
200 Type set to I.
ftp> cd /tmp
250 CWD command successful.
ftp> get test test2
200 PORT command successful.
150 Opening BINARY mode data connection for test (104857600 bytes).
226 Transfer complete.
local: test2 remote: test
104857600 bytes received in 2 seconds (50724.56 Kbytes/s)
ftp>

How to bridge a loopback interface on Mac OSX ?

Hi !
I would like to know how to bridge a loopback interface lo0 to the ethernet interface en0 . The en0 gets an ip address from a modem which act as a DHCP server; en0 has currently an ip add of 192.168.0.10.
Thanks for your help
Christian

Is there a way to do this?
YES my friend there is away, i do it by myself and it's work well…
Here are the steps:
1. go to "/Applications/Mail " and "get info" for your mail and look how much is size of it.
2. from "/Applications/Utilities" open "Disk Utility"app.
3. from file menu select "Blank Disk Image".
4. Save as: "chose the name you want" I save it as "Mail".
    Where: "Better to be on Applications Folder" or in Privet Place on your hard.
    Name: "chose the name you want" I name it as "Mail".
    Size: set the size Bigger than the size of Mail you take it from "mail info".
    Format: Mac OS Extended (Journaled).
    Encryption: 128-bit AES encryption.
    Partitions: Hard disk.
    Image Format: sparse disk image.
5. when you finish Press "Create".
6. Enter the Password You need, be sure to remove the mark next to "Remember password in my keychain".
7. press "OK".
8. you will find new hard disk open on desktop called "the name you chose it before".
9. now copy "Mail.app" to the new hard disk, and remove mail.app to trash but don't empty it. "if you can't delete the app get the info of it and make all the Permissions Names Read & Write" you need Administrator password to open the lock down below.
10. now remove the mail shortcut in Dock and drag the Mail.app you copy it to Dock.
11. now Eject the new Hard disk.
12. open mail from the Shortcut you add… it's will ask you for a Password.
Be sure to Eject the hard disk when you finish from mail.
DONE

Interfaces on a switch 2

What makes an interface on a switch go up?

Duplicate post. please use the link to post answers into the other thread -
https://supportforums.cisco.com/thread/2261484?tstart=0
Jon

Loopback interface on catalyset switches

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