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According to wikipedia host is

A network host is a computer or other device connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network layer host address.

Computer is a host. Printers also provide services and have ip address.

So in these which are really host?

  • router,
  • printer,
  • "Camera in network",
  • switch

I'm totally confused with these things. Thanks in advance

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  • I would say of those four things listed, all four are nodes and the printer could be considered a host. Normally I only use "host" for servers and I rarely use that term at all. But I use the term "node" quite often for anything connected to a network. The wikipedia definition would probably consider the first three to be hosts and the switch might be a host or node depending on whether it has an IP. "Host" is often used to mean any node that has an IP address. Note that there are many network devices that don't need an IP address to do what they are meant to do.
    – Todd Wilcox
    Jun 24, 2015 at 12:52
  • @ToddWilcox, can you please give examples and situations of devices that don't need an IP address and still be able to communicate with other devices w/ an IP?
    – Abhishek Balaji R
    Jun 24, 2015 at 14:09
  • Wireless access points and switches do not usually require IP addresses do to their jobs. The reason why most of them do have IP addresses is for management and configuration purposes, but many of them can be managed out-of-band over a serial port.
    – Todd Wilcox
    Jun 24, 2015 at 15:41
  • In my experience "node" is used in the context of defining a thing while a "host" is used in the context of defining an address to one of these things.
    – user16171
    Jun 25, 2015 at 8:42
  • I'm Still confused ;)
    – apm
    Dec 29, 2016 at 13:24

8 Answers 8

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23

I actually like the way the IPv6 RFC defines it:

2.  Terminology

   node        - a device that implements IPv6.

   router      - a node that forwards IPv6 packets not explicitly
                 addressed to itself.

   host        - any node that is not a router.

So in your list:
router, printer, "Camera in network", switch

  • A router is a node, a router, and a host
  • A printer is a node, and a host*
  • A Camera is a node, and a host*

*(Provided that it as an IP address configured)

A switch is tricky, because it comes down to how it is configured:

  • A switch without an IP address configured, is neither a host, nor a router, nor a node
  • A switch with an IP address configured is a node and a host for the interface/vlan with the configured IP. For all the other ports, it can be considered a switch without an IP address.

(Both bullet points above consider a switch that is not participating in IP routing. If it is, then you could consider it a Router, and the bullet points above these two can be applied)

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  • 5
    "A router is a node, a router, and a host" How is a router a host if the definition of a host is "not a router"?
    – Mark Murfin
    Jun 24, 2015 at 18:09
  • 7
    Because a router has two functions. The first is to forward packets addressed to other hosts (the quoted definition). The second is to communicate with other devices for control plane functions such as routing protocols or other administrative functions. In that case, the traffic is addressed to the router itself, so it acts as a host.
    – Ron Trunk
    Jun 24, 2015 at 19:59
  • 1
    @markMurfin When someone is sending traffic to the Router, or when the Router is initiating traffic to something else, it is technically acting as a host. Consider any dynamic routing protocol, lets use OSPF. Two OSPF neighbors are sending OSPF messages to each other. They aren't forwarding the OSPF packets. So in this case, the physical device (router) is receiving traffic destined to itself, which is the function of a host. You could consider it as two hosts speaking OSPF to each other.
    – Eddie
    Jun 24, 2015 at 22:33
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    @MarkMurfin You can consider the router as both a router (which is not a host) and a host (which is not a router) combined in one box.
    – user253751
    Jun 25, 2015 at 11:38
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    Is there definitions for same in RFC IPv4? I can not find it RFC for IPv4.
    – apm
    Jul 3, 2015 at 4:02
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The way I have seen it used (and try to enforce myself to more effectively communicate) is that a host is any device that is an endpoint for communication, like a PC, storage, printer, etc. Node, like the wikipedia article suggests, is a more general term for any defineable point on the network where information might start, sit, or change directions; so this includes hosts along with switches and other devices that only serve to move the data, they don't "host" it themselves. I try to use the term host where possible, and use the term node when a device is not a host or not doing host-like duties.

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  • So can you tell me the actual difference? Is that addressing or something else?
    – apm
    Jun 24, 2015 at 12:18
  • 2
    All hosts are nodes but not all nodes are hosts. A host hosts something, like a service or data. A node is just anything connected to a network.
    – Todd Wilcox
    Jun 24, 2015 at 12:51
3

The easiest rule is to go by how much network stack is implemented.

A node is any device that is "active" in the network (=has a network port and is more than an electrical adapter); a node may have only a partial network stack, e.g. only physical layer or only physical to network layer.

A host has a complete network stack from physical to application layer, arbitrary applications run on a host.

All strict definitions fail when you look at real-world devices like switches or routers with a web interface - here you'll have to look at what function the device serves in the network. A managed switch is primarily a node and only incidentally a host.

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3

I think the short answer is that usage varies and is really a matter of emphasis.

RFC 1122 Requirements for internet hosts says "A host computer, or simply "host," is the ultimate consumer of communication services. A host generally executes application programs on behalf of user(s), employing network and/or Internet communication services in support of this function. An Internet host corresponds to the concept of an "End-System" used in the OSI protocol suite."

The corresponding RFC 1009 Requirements for internet gateways gives this definition: "A gateway is connected to two or more networks, appearing to each of these networks as a connected host. Thus, it has a physical interface and an IP address on each of the connected networks."

The general idea of host as being an actual target of communications seems the most usual, but purposive, description. For a network engineer, a router or switch or UPS might well be a host -- a thing to be talked to. For a person using web banking, routers are just plumbing.

Kind regards

Jonathan.

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2

In my understanding, a host is an end system/device, which can host /run applications. A host could be a Client or a Server. The type of application differs in both these cases.

The nodes will not know much about the applications.

In your question, router and switch are nodes, while a camera and printer can be considered as hosts.

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A network node has an OSI layer 1 network hardware interface with a hard-coded OSI layer 2 physical address. This hardware address type is for data transmissions which are recognized only within its own network segment and are not routable by themselves.

A network host, is also a node, but has an additional OSI layer 3 logical address as well. This logical address is what makes routable data communications between distant/separate/dissimilar networks possible.

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Hosts are computers whereas nodes are all devices that have network addresses assigned. So, a router is not a host but is a node.

Node (networking) Wikipedia
In data communication, a physical network node may either be a data communication equipment (DCE) such as a modem, hub, bridge or switch; or a data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer, for example a router, a workstation or a server.

If the network in question is the Internet or an Intranet, many physical network nodes are host computers, also known as Internet nodes, identified by an IP address, and all hosts are physical network nodes. However, some datalink layer devices such as switches, bridges and WLAN access points do not have an IP host address (except sometimes for administrative purposes), and are not considered to be Internet nodes or hosts, but as physical network nodes and LAN nodes.

Host (network) Wikipedia
Every network host is a physical network node (i.e. a network device), but not every physical network node is a host. Network devices such as modems, hubs and network switches are not assigned host addresses (except sometimes for administrative purposes), and are consequently not considered to be network hosts. Devices such as network printers and hardware routers have IP addresses, but since they are not general-purpose computers, they are sometimes not considered to be hosts.

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  • So switch is a physical node, but not a network node?
    – apm
    Jun 26, 2015 at 4:33
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To summarize - host = entertains the guests with data / services

nodes / routers / switches / LBs / FWs = move the traffic to the hosts

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1
  • A client computer is also a host...
    – Zac67 ♦
    Oct 3, 2017 at 16:44

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