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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.

39
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1answer
4k views

Why is such a large IPv4 range assigned to localhost?

Why is so large a range of IPv4 addresses assigned to localhost, (127.0.0.0 through 127.255.255.255)?
19
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2answers
5k 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 ...
12
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1answer
2k 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-...
10
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2answers
12k views

why we can't create multiple loopback interfaces in Junos?

comparing to Cisco IOS , we can create any number of loopbacks on router , but on Junos you can create only one loopback interface (even logical units from same loopback) in the routing instance , ...
9
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3answers
10k 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 ...
6
votes
1answer
825 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.
4
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1answer
490 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. ...
3
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2answers
1k 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.
3
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1answer
209 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 ...
3
votes
1answer
206 views

Consequences of an intra-switch Loopback cable

I am using Dell switch and I looped it to itself. If I enable STP on 2 ports, what happen the port states? I have attached the topology below. Let me know, if you need clarification.
3
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1answer
1k 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 ...
3
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2answers
4k 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 ...
2
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1answer
203 views

What is loopback under certain port of a router?

Cisco#sh interfaces GigabitEthernet0/0 GigabitEthernet0/0 is up, line protocol is up Hardware is CN Gigabit Ethernet, address is 6400.f13b.bec0 (bia 6400.f13b.bec0) Description: $ETH-LAN$$ETH-...
2
votes
1answer
85 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 ...
2
votes
2answers
429 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.
2
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2answers
458 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 ...
2
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1answer
1k 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?
2
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1answer
78 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 ...
2
votes
1answer
740 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. ...
2
votes
1answer
1k 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 ...
2
votes
1answer
37 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 ...
1
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4answers
732 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 ...
1
vote
1answer
78 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 ...
1
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2answers
367 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....
1
vote
1answer
62 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 ...
1
vote
1answer
459 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. ...
1
vote
1answer
453 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 ...
1
vote
2answers
653 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 ...
1
vote
0answers
84 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....
0
votes
2answers
73 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 ...
0
votes
1answer
307 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 ...
0
votes
1answer
570 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 ...
0
votes
0answers
23 views

Does a loop back IP address not need to be assigned to a network interface, in order to communicate with? [duplicate]

ifconfig shows only one loopback address 127.0.0.1 and that it is assigned to network interface lo. ping 127.0.0.2 can receive packets back, even though 127.0.0.2 is not assigned to a (virtual) ...
0
votes
1answer
57 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 ...