computer networking A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...

, a host model is an option of designing the

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

stack of a networking

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

. When a

unicast Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a one-to-one transmission from one point in ...

packet arrives at a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

, IP must determine whether the packet is locally destined (its destination matches an address that is assigned to an interface of the host). If the IP stack is implemented with a weak host model, it accepts any locally destined packet regardless of the network interface on which the packet was received. If the IP stack is implemented with a strong host model, it only accepts locally destined packets if the destination IP address in the packet matches an IP address assigned to the network interface on which the packet was received. The weak host model provides better network connectivity (for example, it can be easy to find any packet arriving at the host using ordinary tools), but it also makes hosts susceptible to multihome-based network attacks. For example, in some configurations when a system running a weak host model is connected to a VPN, other systems on the same subnet can compromise the security of the VPN connection. Systems running the strong host model are not susceptible to this type of attack. The

IPv4 Internet Protocol version 4 (IPv4) is the first version of the Internet Protocol (IP) as a standalone specification. It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. ...

implementation in

versions prior to

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

uses the weak host model. The

and

Windows Server 2008 Windows Server 2008, codenamed "Longhorn Server" (alternatives: "Windows Vista Server" or "Windows Server Vista"), is the seventh major version of the Windows NT operating system produced by Microsoft to be released under the Windows Server b ...

stack supports the strong host model for both IPv4 and

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

and is configured to use it by default. However, it can also be configured to use a weak host model. The

implementation in

defaults to the weak host model. Source validation by reversed path, as specified in RFC 1812 can be enabled (the rp_filter option), and some distributions do so by default. This is not quite the same as the strong host model, but defends against the same class of attacks for typical multihomed hosts. arp_ignore and arp_announce can also be used to tweak this behaviour. Modern BSDs (

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

NetBSD NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was fork (software development), forked. It continues to ...

OpenBSD OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD ...

, and DragonflyBSD) all default to the weak host model. OpenBSD since 6.6-current supports strong host model by default "if and only IP forwarding is disabled", with IP forwarding enabled (and for older versions) it supports reversed path source validation via its pf firewall, using the urpf-failed option, while Free-, Net-, and DragonflyBSD provide a global

sysctl sysctl is a software mechanism in some Unix-like operating systems that reads and modifies the attributes of the system kernel such as its version number, maximum limits, and security settings. It is available both as a system call for compile ...

options.

References

External links

* - Requirements for Internet Hosts -- Communication Layers * {{DEFAULTSORT:Host model Internet protocols Computer networking

See also

References

External links