Questions tagged [loopback]

For questions about loopback interfaces on network devices. For instance, you want to configure routing on your layer 3 switch and for that you want to configure a loopback interface.

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Why will specifying the outgoing physical interface work for a static route with IPv4 and not for IPv6?

When setting up loopback interfaces with IPv6 addresses with static routes between two directly connected routers through their interfaces. It does not work to specify it with the outgoing physical ...
Calvin Broadus's user avatar
7 votes
9 answers
4k views

Why can I send 127.0.0.1 to 127.0.0.0 on my network?

We have a product that runs over IP. This product comes in two halves that are supposed to be connected directly to each other over Cat 5e. All this works fine. For reasons that are not important, we ...
David Anderson's user avatar
1 vote
2 answers
530 views

What is the loopback Ethertype?

IANA's list of IEEE 802 Ethertypes includes an entry for Loopback (0x9000). However, I cannot find any specification detailing exactly how this is implemented. Do frames sent with Ethertype 0x9000 ...
Ben Zelnick's user avatar
0 votes
1 answer
867 views

How to connect GNS3 to loopback adapter on Windows 10

I'm trying to have a simple topology by connecting a router (c7200) and the local machine which is windows 10. For this I use GNS3 GUI (not the VM application). I have to do that, due to the limit of ...
manula's user avatar
  • 1
1 vote
1 answer
656 views

Test communication of interface using Cat5E loopback

So I need to create a simple process to test a large amount of gigabit network ports. Since I don't want to setup two machines and run software on both the test connection my first thought was to ...
John Smith's user avatar
2 votes
1 answer
251 views

RIP routes are not being advertised

I have 2 routers(R3 and R4 connected with serial links). I have advertised my loopbacks with RIP ver 2. with 192.168.1.1/32 and 192.168.2.1/32 on R3 and 192.168.3.1/32 and 192.168.4.1/32 on R4. My ...
Anjil Khadka's user avatar
2 votes
2 answers
991 views

Can Loopback IP be Public

I have a Usecase where an Access Device need to reach a Core Device over the Internet. Access Device is configured with the Public IP of the Core device as of now so that it can reach the Core over ...
Alex's user avatar
  • 21
0 votes
1 answer
100 views

Connectivity issues with 127.x.x.x series [closed]

I have a couple of servers with the below config server1: lo: 127.0.0.1/16 scope host eno1: 127.15.0.1/16 scope global eno2: 5.0.0.1/24 server2: lo: 127.0.0.1/16 (it had /8. I changed the subnet ...
RBK050's user avatar
  • 1
2 votes
1 answer
139 views

EUI-64 on a loopback address

A loopback address does not have a MAC address. How then does a loopback interface get assigned an EUI-64 address? I ran an example on packet tracer, and the loopback interface successfully acquired a ...
Zee's user avatar
  • 35
0 votes
1 answer
845 views

How to configure loopback for switch management

We have Cisco Switches (Nexus 93). My PC is on vxlan, in vrf "test" with default gateway 60.254. We want to use loopback 99 for managent for switches. We have created a loopback 99 with an ...
Магомед Рабаданов's user avatar
0 votes
2 answers
611 views

I have set static routes on both routers, Why can't I ping between the loopback interfaces?

This is my test topology: R6---R7 the interface IP address I have configured on it, you can check in the snapshot. and in both routers I have configured the static route, in R6 10.0.0.22/32 out ...
244boy's user avatar
  • 1,767
0 votes
0 answers
119 views

AVAYA Internal Loopback test failed during boot

Today, suddenly our network went down and I cannot get it up so far. I noticed that our core switch was not functioning. I tried to reboot it but no luck. Then I noticed that it can not pass a test ...
Mustafa's user avatar
  • 101
0 votes
1 answer
39 views

Ping using 127.0.0.1 [closed]

My question is about this case : I have a PC with 2 NIC (Network interface card ) , when I do ( ping 127.0.0.1) ** which nic will be the ping tested on ? **
sulaimansaleh Zd's user avatar
0 votes
1 answer
231 views

Loopback interfaces subnets [closed]

Assuming that loopback interface is always alone in its network, what are the practical reasons to have IPv4 subnet prefix shorter than /32 for these interfaces? Moreover, why according to various ...
Eugene D. Gubenkov's user avatar
0 votes
2 answers
288 views

Loopback interface

I have a theoretical question about the loopback implementation on a router. I understand that the idea of a loopback interface is that it is a virtual interface which never goes down due to a ...
White Philosophy's user avatar
1 vote
1 answer
532 views

What happens if the localhost does not interpret 127.0.0.1 as the loopback address?

For the sake of the example, assume gateway to be 10.0.0.1 and host A (my machine) to be 10.0.0.2. If gateway (10.0.0.1) is running a service bound to a port on localhost only, the service should be ...
user9123's user avatar
  • 113
0 votes
0 answers
349 views

Juniper MX Routing Engine Firewall Filter

I'm having difficulties with something I initially thought would be rather simple. I need to apply an outbound firewall filter on an MX10003's management interface. I'm currently using Lo0.0 as the ...
Ben's user avatar
  • 157
1 vote
2 answers
2k views

Loopback with / 32

When we dealing with bgp, osp. Why do we especially use loopback interfaces with / 32!? Is there an advantage or something different from other subnets like 24.
Anas Majzoob's user avatar
3 votes
1 answer
250 views

No packets showing up in Wireshark despite Client-Server communication

I am somewhat new to computer networking and I created a little project where I have two computers connected to an Ethernet switch, forming a small network. Computer server (192.168.1.1) has a mail-...
Mantabit's user avatar
  • 141
0 votes
2 answers
1k views

While sniffing with Wireshark, i get lot of ICMP packets in my loop back interface with the word "CKAAAA.." in it, why is this happening? [closed]

So i have a parrot VM, and i tried to use wireshark on the lo interface of it just for fun, now I'm seeing loads of ICMP packets, which seems to be Netbios inside(not sure why is Wireshark naming the ...
Mery Ted's user avatar
  • 101
1 vote
0 answers
97 views

Loopback on T1 not showing up [closed]

I'm a T1 tech for a major US ISP. We regularly remotely loopback T1s (at the smartjack) and test them before the installation. Recently I got 3 new T1s in a bundle that acted weird, and I hoping you ...
Somenath Sinha's user avatar
4 votes
1 answer
490 views

Which physical interface would be used to send/receive packets intended for a loopback interface?

Let us say, I have configured the managed router with a loopback addresses - Interface IP-Address OK? Method Status Protocol GigabitEthernet0/0 ...
Deepak's user avatar
  • 697
1 vote
1 answer
721 views

Does sending a packet to a private IP adrress for a local network interface work in the same way as sending it to a loopback address?

On my local host, there is a loopback address 127.0.0.1, and a wifi interface with private address 192.168.1.97 assigned by the local wifi network. Do both the loop back and private IP addresses ...
Tim's user avatar
  • 1,545
0 votes
2 answers
3k views

Loopback Interface speed is 10 Mbps but Incoming and Outgoing Traffic is in Gbps

I am writing a script which mails interface data to network admin. For this I'm using LibreNMS and RRDTool to gather data. On inspecting one of the loopback interfaces, I found that the interface ...
Giridhar Shenoy's user avatar
2 votes
1 answer
868 views

Should the Loopback address be unique across the network?

I have an MPLS network where every site has two PEs for redundancy. and I want to configure a set of loopback interfaces on every PE router for routing traffic between different VRFs. is it possible ...
Forrest's user avatar
  • 57
1 vote
1 answer
548 views

Connecting eBGP and iBGP routers in Quagga

I am trying to run intra and inter-domain routing using Quagga. I like to announce a prefix from AS7 and I like AS6 receive it and send it to AS2(as shown in the attached topology). I know for intra ...
Shahrooz Pooryousef Delezi's user avatar
20 votes
2 answers
6k views

What is the difference between 0.0.0.0 and a loopback IP address?

From the book Computer Network: The IP address 0.0.0.0, the lowest address, is used by hosts when they are being booted. It means ‘‘this network’’ or ‘‘this host.’’ ... All addresses of the ...
Tim's user avatar
  • 1,545
1 vote
1 answer
435 views

What's the relationship of a Router with its loopback interface in logic?

I have a Router1 with a loopback 0 connected to the Router2: the interface brief is bellow: Router1>show ip interface brief Interface IP-Address OK? Method Status ...
aircraft's user avatar
  • 1,138
0 votes
1 answer
1k views

Wireshark capture on LoopBack interface [closed]

We have two applications running on same machine, both of them are listening on the loopback interface on two different ports. Client Application is sending data to server, but receiving Application ...
Niranjan Upadhya's user avatar
2 votes
1 answer
200 views

IP address that can not be reached from outside of device

I am sorry if this is a silly question, but I am developing an application that should connect to itself over sockets, but to make it secure it should only be reachable from local device. I believe I ...
JustHobby's user avatar
  • 123
2 votes
1 answer
2k views

Npcap Loopback Adapter not showing PING results in Wireshark

I've a server process and a client process running on my machine. To capture the packets transmitted between them, I've installed the Npcap Loopback Adapter as suggested in the ever-so-famous ...
Kushal Kumar's user avatar
2 votes
2 answers
2k views

Ping loopback without interface IP address

I have two routers attached directly and both of them has loopback address. The interface has no IP address, I have just connected R1 g0/0 to R5 g0/0. If I put IP address on the g0/0 interface of both ...
shakAttack's user avatar
1 vote
2 answers
4k views

BGP update source basics

I have the following test lab: The configuration of 'King' is: King#sho ip int bri Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192....
fsociety's user avatar
  • 893
3 votes
1 answer
2k views

Setting a loopback/management address through a layer 2 trunk

We have two EX4200 switches in the following configuration: Router (.1)=====static route=====(.2) EX_01========trunk========EX_02 I want to configure a loopback or management interface on EX_02. ...
Chris's user avatar
  • 191
1 vote
4 answers
2k views

STP not preventing switching loop

I have a TP Link managed switch that I have enabled STP in, but it's not detecting a loop in the network, and brings the entire lan down. I plug two ends of an Ethernet cable into the switch, which ...
user4757174's user avatar
6 votes
2 answers
3k views

Why can I ping IP addresses from 127.0.0.1 to 127.255.255.254?

I thought that the loopback IP address of my machine is 127.0.0.1. I do not understand why am I able to ping IP addresses until 127.255.255.254.
yoyo_fun's user avatar
  • 1,531
1 vote
1 answer
1k views

Loopback interfaces aren't advertised via RIPv2

My topology is as so R0 as Hub R1 and R2 as spoke R2 has a loopback of 2.2.2.2, and R3 has a loopback of 3.3.3.3 R1 can ping these addresses, and is advertising 2.0.0.0 and 3.0.0.0 in RIPv2. ...
Josh 's user avatar
  • 13
2 votes
1 answer
3k views

loopback address on switch what is it's scop

Let me know if I am misunderstanding. To me, the loopback from a switch is different from the PC ones. they are both attached to a virtual interface, but for the PC, only it can access it's loopback. ...
pwnsauce's user avatar
  • 211
2 votes
1 answer
4k views

Can my default gateway of router be 127.0.0.1?

So, can I set 127.0.0.1 as the default gateway to my router/modem instead 192.168.1.1? If yes, why?
CivilEngine's user avatar
1 vote
1 answer
726 views

IP NAT Enable - Port Forwarding Range

I'm using NAT Hairpin on a 1841 cisco router, I would like to open a range of ports 5555 - 5574 tcp and 2326 - 2485. All I've been able to find is command for using NAT (inside) / (outside). Anyone ...
Bishop527's user avatar
3 votes
2 answers
7k views

How is harpinning (NAT loopback) used in practice?

I have never had to use hairpinning in the past and so far, reading its description on Wikipedia, I don't see many use cases for this technology, apart from some requests from selected users inside ...
syntagma's user avatar
  • 349
2 votes
2 answers
3k views

What are the most common scenarios in which the 'loopback interface' on a router is used?

I was studying about CISCO routers and we learned that every router has a LOOPBACK interface. How and when are those interfaces used? We never used it though in our configurations.
yoyo_fun's user avatar
  • 1,531
1 vote
2 answers
1k views

Cisco IOS multi WAN with NAT on Loopback0 with ip sla

I am trying to configure WAN redundancy across a pair of links, using ip sla to monitor link state and switch routes if one fails. The design uses Loopback0 as a NAT interface, with the two WAN ...
btongeorge's user avatar
5 votes
1 answer
3k views

Routing loopback using OSPF

Here is a simple network using OSPF. Router2 has got LoopBack0 with IP address 10.0.2.1 255.255.255.0. I add this network to OSPF: Router(config-router)#net 10.0.2.0 0.0.0.255 area 0 When I dispaly ...
DavidM's user avatar
  • 284
2 votes
1 answer
65 views

While configuring OSPF the router-Id has the highers ip address?

What is meant by the sentence - Loopback address is the highest IP address and this means that it is used by OSPF router to advertise the routing information. For example - f 0/0 -- 192.168.45.4 ...
Shreyas Joshi Joshi's user avatar
1 vote
1 answer
145 views

「Netscreen」 VPN UP/DOWN due to loopback address source monitoring

I am dealing with a problem with Netscreen VPN. Topology is basically Server Side ーー> (Agg2)Trust/Untrust(Agg1)ーー> ーー> Remote Office (Yamaha) 100.66.xx.0/24 ーー> Netscreen VPN ーー> Internet ーー> 100....
Tooru's user avatar
  • 11
1 vote
1 answer
986 views

Is NAT loopback the only reason I can't view my own website from within my LAN? [closed]

I am new to this so apologies if this is the wrong place for such a question. I'm testing out a simple "hello world" website hosted at home. As we have not been assigned a static IP address by our ...
rfrank's user avatar
  • 11
11 votes
3 answers
33k views

Whats's the function of a loopback interface in routing protocols?

So I've got this task where I have to setup a virtual network with an OSPF routing protocol. I firstly ignored this loopback interface I had to configure on the routers since it didn't do any ...
iPh1ps99's user avatar
  • 153
15 votes
1 answer
4k views

Under what circumstances are multiple loopback (127/8) addresses useful?

I made an app in java where a client sends ip-packets to a server via the looback-address 127.0.0.1. A really simple app just to test how things work. At first I thought If I created several client-...
Björn Hallström's user avatar
2 votes
2 answers
883 views

IP stack and loopback address

The IP address 127.0.0.1 is used to test the IP stack on an individual node. What is IP stack here ?Some blogs redirects this question to TCP/IP stack.But I am unable to co relate and understand it.
Abhishek's user avatar