In computer networking, a host model is an option of designing the TCP/IP stack of a networking operating system like

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

or Linux. 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 People *Jim Host (born 1937), American businessman * Michel Host ...

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

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 fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...

implementation in

versions prior to Windows Vista uses the weak host model. The Windows Vista and Windows Server 2008 TCP/IP stack supports the strong host model for both IPv4 and IPv6 and is configured to use it by default. However, it can also be configured to use a weak host model. The

implementation in Linux 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 and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

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

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project em ...

, and

DragonflyBSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in Jun ...

) 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 options.

References

External links

* - Requirements for Internet Hosts -- Communication Layers * Internet protocols Computer networking {{network-software-stub

See also

References

External links