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33 votes
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Why are IP addresses given to each interface and not device? What would the implications of that be?

Connecting an interface to a network makes it a part of that network. Therefore, the IP address is a property of the connection, not the host. Likewise, a host can have many network connections and ...
Zac67's user avatar
  • 85.8k
31 votes
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Is multicast on the public internet possible? And if yes: How?

You cannot multicast on the public Internet, but you can multicast across the public Internet to another site by using a tunnel that supports multicast. Multicast routing is very different from ...
Ron Maupin's user avatar
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21 votes
Accepted

Is it possible to specify a route for a packet to take?

It's theoretically possible, but not really in a practical sense. The IP protocol includes two options: Loose Source and Record Route (LSRR) Strict Source and Record Route (SSRS) They're both ...
Barmar's user avatar
  • 426
20 votes
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Does anycast addressing add additional latency in any way?

Does anycast addressing, in itself, add any additional latency to network connections? No. one using unicast and the other using anycast Anycast is unicast. It is just that the same network is ...
Ron Maupin's user avatar
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19 votes
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Why can't devices in different subnets talk with each other?

Devices in different subnets can communicate. That is the purpose of a router. Routers route packets between different networks. Even if devices in different networks are on the same layer-2 ...
Ron Maupin's user avatar
  • 100k
19 votes

Is multicast on the public internet possible? And if yes: How?

As an end-user, you cannot multicast across the Internet, unless using a tunnel. As a larger organization, like a video provider or an ISP, it is certainly possible to forward multicast packets ...
pHeoz's user avatar
  • 590
18 votes
Accepted

How does a router find the next hop when the receiver is in a distant IP network?

Say I want to send a frame to a web server, and let's say this web server is in a very distant IP outside my local network e.g. a Google server. You're sending packets to remote destinations. Frames ...
Zac67's user avatar
  • 85.8k
17 votes

Why are IP addresses given to each interface and not device? What would the implications of that be?

It would not be enough. Suppose I have a computer with three interfaces: eth0 (wired Ethernet), wlan0 (wifi), and vboxnet0 (virtualbox). One of the interfaces is connected to an internal network, one ...
Piskvor left the building's user avatar
15 votes
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netstat -nr returning "0/1" -- what does that mean?

Some VPNs push the default gateway (a /0 netmask) as two /1 networks: 0/1 and 128/1. Since a more specific route always wins, this forces traffic to be routed via the VPN instead of over the default ...
Teun Vink's user avatar
  • 17.4k
14 votes
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RIB vs FIB differences?

The forwarding information base (FIB) is the actual information that a routing/switching device uses to choose the interface that a given packet will use for egress. For example, the FIB might be ...
rnxrx's user avatar
  • 6,124
14 votes
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What is the difference between routing table and forwarding table?

In routers you normally have two separate planes, often called "control plane" and "forwarding plane". The control plane is the "brain" of the router and handles things as management of the device ...
Sebastian Wiesinger's user avatar
14 votes

Do routers change MAC address of packets when forwarding

When a frame comes into a router, the router strips off and discards the frame, losing any layer-2 addressing, including MAC addresses. The router will build a new frame for the next interface. Not ...
Ron Maupin's user avatar
  • 100k
13 votes
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IPv6 and online privacy and security

Let's look at a live example. This being from my Linux workstation. (And for simplicity I actually omitted a couple of addresses.) I'll explain each of the addresses in turn: $ ip a s dev br0 3: br0: &...
Michael Hampton's user avatar
13 votes
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Is policy routing bad?

Normally, a router forwards packets based on destination address alone. This is obviously very simple and efficient. Policy-based routing means the router is now looking at other factors to ...
Ted Quanstrom's user avatar
13 votes

How to setup self hosting with redundant Internet connections?

In your question, you're broadly describing the concepts implemented by Border Gateway Protocol (BGP), a signaling protocol "big" Internet routers use to coordinate the Internet routing ...
Jeff Wheeler's user avatar
  • 5,532
12 votes
Accepted

What is the difference between broadcasting and flooding?

Broadcasting is a term that is used on a broadcast domain, which is bounded by layer-3 (routers). Broadcasts are sent to a special broadcast address, both for layer-2 and layer-3. A broadcast cannot ...
Ron Maupin's user avatar
  • 100k
12 votes
Accepted

Is rerouting possible in UDP?

This is not the hosts that decide which route a packet will follow, each router in the path make it's own decision. (Actually, the originating host could use the IP strict source option to try to ...
JFL's user avatar
  • 19.8k
12 votes
Accepted

Dealing with IP Spoofing

It means that a packet received from outside the local network could have a source address of the inside network. That would be for a malicious purpose. The router could be configured to check the ...
Ron Maupin's user avatar
  • 100k
11 votes
Accepted

Must the checksum field of the IPv4 header always be updated?

Since the router changes the IPv4 header (it decrements the TTL), it needs to calculate a new value for the checksum, otherwise subsequent devices receiving the packet will think it is damaged. This ...
Ron Maupin's user avatar
  • 100k
11 votes
Accepted

Difference between routing, forwarding, and switching

In general, forwarding refers to a device sending a datagram to the next device in the path to the destination, switching refers to moving a datagram from one interface to another within a device, and ...
Ron Maupin's user avatar
  • 100k
11 votes

routing between vlans not working

You don't have NAT enabled (you don't have ip nat outside on Vl 20). Without NAT, the ISP doesn't know how to route back to your 192.9.200.0 network. If you NAT to the VLan 20 address, the ISP ...
Ron Trunk's user avatar
  • 67.8k
10 votes
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How are IPv4 Addresses provided uniquely to domains?

Who mainly provides IP addresses to domains? As in, who commands, "www.google.com, 103.233.38.93 is yours; www.stackexchange.com I will assign 104.16.115.182 to you; etc." Normally IP addresses are ...
Peter Green's user avatar
  • 13.5k
10 votes
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What does a switch do when the destination MAC address is unknown?

I think you are confused. The destination MAC address for any destination not on your LAN is the MAC address of the gateway configured in your source host. MAC addresses are layer-2 addresses, and ...
Ron Maupin's user avatar
  • 100k
10 votes
Accepted

OSPF without Area 0

There is only one way to use OSPF without an Area 0, and that is to use OSPF with a single area. If you only have one OSPF area, you can number it any way you like, but if you have even two areas, you ...
Ron Maupin's user avatar
  • 100k
10 votes

BGP vs OSPF path selection with /24 vs /23`

The route with the longest mask (/24) is always preferred regardless of how it’s learned. The protocol doesn’t matter.
Ron Trunk's user avatar
  • 67.8k
10 votes
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Is it true that the fd00::/8 address range (ULA) in ipv6 is for machines that you NEVER want to speak with anything on the Internet?

IPv6 packets addressed in the IPv6 ULA address range, fc00::/7, can not be routed on the public Internet. Remember, though, that interfaces can have multiple IPv6 addresses, including Link-Local, ...
Ron Maupin's user avatar
  • 100k
10 votes
Accepted

At which layer does router operate?

Network address translation (NAT) is a feature of Router which is required for routing traffic. That is completely incorrect. NAT is a kludge (a clumsy, inefficient solution) designed to extend the ...
Ron Maupin's user avatar
  • 100k
10 votes
Accepted

Do we send ack frames in ethernet? if not then how does a router know if its neighbors are down or not?

No, ethernet is connectionless, as is IP, and if you use UDP, the application would need to perform any connection-related handshaking (if needed). Typically, it is the responsibility of the transport ...
Ron Maupin's user avatar
  • 100k
10 votes
Accepted

How not to route on a Cisco router

While Ron and Ron's answers actually enable routing but prevent traffic, their suggestions still pack both host groups into the same routing instance. There's another way to think about this: a) ...
Marc 'netztier' Luethi's user avatar
10 votes

Why are IP addresses given to each interface and not device? What would the implications of that be?

A device that has an IP address exists within a network. A Router is a device who's primary purpose is to pass traffic between networks. For a Router to pass packets between two networks, it must ...
Eddie's user avatar
  • 15.1k

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