Network Device Router
A router is a networking device that forwards data
packets between computer networks. Routers perform the traffic directing
functions on the Internet. Data sent through the internet, such as
a web page or email, is in the form of data packets. A packet is
typically forwarded from one router to another router through the
networks that constitute an internetwork until it reaches its
destination node.
A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the network address information in the packet to determine the ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey.
The most familiar type of routers are home and small office routers that simply forward IP packets between the home computers and the Internet. An example of a router would be the owner’s cable or DSL router, which connects to the Internet through an Internet service provider (ISP). More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, software-based routers also exist.
Operation
When multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a routing protocol. Each router builds up a routing table listing the preferred routes between any two systems on the interconnected networks.
A router has two types of network element components organized onto separate planes:
1.Control plane: A router maintains a routing table that lists which route should be used to forward a data packet, and through which physical interface connection. It does this using internal preconfigured directives, called static routes, or by learning routes dynamically using a routing protocol. Static and dynamic routes are stored in the routing table. The control-plane logic then strips non-essential directives from the table and builds a forwarding information base (FIB) to be used by the forwarding plane.
2.Forwarding plane: The router forwards data packets between incoming and outgoing interface connections. It forwards them to the correct network type using information that the packet header contains matched to entries in the FIB supplied by the control plane.
Applications
A router may have interfaces for different types of physical layer connections, such as copper cables, fiber optic, or wireless transmission. It can also support different network layer transmission standards. Each network interface is used to enable data packets to be forwarded from one transmission system to another. Routers may also be used to connect two or more logical groups of computer devices known as subnets, each with a different network prefix.
Routers may provide connectivity within enterprises, between enterprises and the Internet, or between internet service providers’ (ISPs’) networks. The largest routers (such as the Cisco CRS-1 or Juniper PTX) interconnect the various ISPs, or may be used in large enterprise networks. Smaller routers usually provide connectivity for typical home and office networks.
All sizes of routers may be found inside enterprises. The most powerful routers are usually found in ISPs, academic and research facilities. Large businesses may also need more powerful routers to cope with ever-increasing demands of intranetdata traffic. A hierarchical internetworking model for interconnecting routers in large networks is in common use.
Access, core and distribution
Access routers, including small office/home office (SOHO) models, are located at home and customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost. Some SOHO routers are capable of running alternative free Linux-based firmware like Tomato, OpenWrt or DD-WRT.
Distribution routers aggregate traffic from multiple access routers. Distribution routers are often responsible for enforcing quality of service across a wide area network (WAN), so they may have considerable memory installed, multiple WAN interface connections, and substantial onboard data processing routines. They may also provide connectivity to groups of file servers or other external networks.
In enterprises, a core router may provide a collapsed backbone interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth, but lack some of the features of edge routers.
Security
External networks must be carefully considered as part of the overall security strategy of the local network. A router may include a firewall, VPN handling, and other security functions, or these may be handled by separate devices. Many companies produced security-oriented routers, including Cisco PIX series, Cisco Meraki MX series and Juniper NetScreen. Routers also commonly perform network address translation (which allows multiple devices on a network to share a single public IP address) and stateful packet inspection. Some experts argue that open source routers are more secure and reliable than closed source routers because open source routers allow mistakes to be quickly found and corrected.
Internet connectivity and internal use
Routers intended for ISP and major enterprise connectivity usually exchange routing information using the Border Gateway Protocol (BGP). RFC 4098 standard defines the types of BGP routers according to their functions:
Edge router: Also called a provider edge router, is placed at the edge of an ISP network. The router uses External BGP to EBGP routers in other ISPs, or a large enterprise Autonomous System.
Subscriber edge router: Also called a Customer Edge router, is located at the edge of the subscriber’s network, it also uses EBGP to its provider’s Autonomous System. It is typically used in an (enterprise) organization.
Inter-provider border router: Interconnecting ISPs, is a BGP router that maintains BGP sessions with other BGP routers in ISP Autonomous Systems.
Core router: A core router resides within an Autonomous System as a back bone to carry traffic between edge routers.
Within an ISP: In the ISP’s Autonomous System, a router uses internal BGP to communicate with other ISP edge routers, other intranet core routers, or the ISP’s intranet provider border routers.
“Internet backbone:” The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks. See default-free zone (DFZ). The major ISPs’ system routers make up what could be considered to be the current Internet backbone core. ISPs operate all four types of the BGP routers described here. An ISP “core” router is used to interconnect its edge and border routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching protocols.
Port forwarding: Routers are also used for port forwarding between private Internet-connected servers.
Voice/Data/Fax/Video Processing Routers: Commonly referred to as access servers or gateways, these devices are used to route and process voice, data, video and fax traffic on the Internet. Since 2005, most long-distance phone calls have been processed as IP traffic (VOIP) through a voice gateway. Use of access server type routers expanded with the advent of the Internet, first with dial-up access and another resurgence with voice phone service.
Larger networks commonly use multilayer switches, with layer 3 devices being used to simply interconnect multiple subnets within the same security zone, and higher layer switches when filtering, translation, load balancing or other higher level functions are required, especially between zones.
A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the network address information in the packet to determine the ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey.
The most familiar type of routers are home and small office routers that simply forward IP packets between the home computers and the Internet. An example of a router would be the owner’s cable or DSL router, which connects to the Internet through an Internet service provider (ISP). More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, software-based routers also exist.
Operation
When multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a routing protocol. Each router builds up a routing table listing the preferred routes between any two systems on the interconnected networks.
A router has two types of network element components organized onto separate planes:
1.Control plane: A router maintains a routing table that lists which route should be used to forward a data packet, and through which physical interface connection. It does this using internal preconfigured directives, called static routes, or by learning routes dynamically using a routing protocol. Static and dynamic routes are stored in the routing table. The control-plane logic then strips non-essential directives from the table and builds a forwarding information base (FIB) to be used by the forwarding plane.
2.Forwarding plane: The router forwards data packets between incoming and outgoing interface connections. It forwards them to the correct network type using information that the packet header contains matched to entries in the FIB supplied by the control plane.
Applications
A router may have interfaces for different types of physical layer connections, such as copper cables, fiber optic, or wireless transmission. It can also support different network layer transmission standards. Each network interface is used to enable data packets to be forwarded from one transmission system to another. Routers may also be used to connect two or more logical groups of computer devices known as subnets, each with a different network prefix.
Routers may provide connectivity within enterprises, between enterprises and the Internet, or between internet service providers’ (ISPs’) networks. The largest routers (such as the Cisco CRS-1 or Juniper PTX) interconnect the various ISPs, or may be used in large enterprise networks. Smaller routers usually provide connectivity for typical home and office networks.
All sizes of routers may be found inside enterprises. The most powerful routers are usually found in ISPs, academic and research facilities. Large businesses may also need more powerful routers to cope with ever-increasing demands of intranetdata traffic. A hierarchical internetworking model for interconnecting routers in large networks is in common use.
Access, core and distribution
Access routers, including small office/home office (SOHO) models, are located at home and customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost. Some SOHO routers are capable of running alternative free Linux-based firmware like Tomato, OpenWrt or DD-WRT.
Distribution routers aggregate traffic from multiple access routers. Distribution routers are often responsible for enforcing quality of service across a wide area network (WAN), so they may have considerable memory installed, multiple WAN interface connections, and substantial onboard data processing routines. They may also provide connectivity to groups of file servers or other external networks.
In enterprises, a core router may provide a collapsed backbone interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth, but lack some of the features of edge routers.
Security
External networks must be carefully considered as part of the overall security strategy of the local network. A router may include a firewall, VPN handling, and other security functions, or these may be handled by separate devices. Many companies produced security-oriented routers, including Cisco PIX series, Cisco Meraki MX series and Juniper NetScreen. Routers also commonly perform network address translation (which allows multiple devices on a network to share a single public IP address) and stateful packet inspection. Some experts argue that open source routers are more secure and reliable than closed source routers because open source routers allow mistakes to be quickly found and corrected.
Internet connectivity and internal use
Routers intended for ISP and major enterprise connectivity usually exchange routing information using the Border Gateway Protocol (BGP). RFC 4098 standard defines the types of BGP routers according to their functions:
Edge router: Also called a provider edge router, is placed at the edge of an ISP network. The router uses External BGP to EBGP routers in other ISPs, or a large enterprise Autonomous System.
Subscriber edge router: Also called a Customer Edge router, is located at the edge of the subscriber’s network, it also uses EBGP to its provider’s Autonomous System. It is typically used in an (enterprise) organization.
Inter-provider border router: Interconnecting ISPs, is a BGP router that maintains BGP sessions with other BGP routers in ISP Autonomous Systems.
Core router: A core router resides within an Autonomous System as a back bone to carry traffic between edge routers.
Within an ISP: In the ISP’s Autonomous System, a router uses internal BGP to communicate with other ISP edge routers, other intranet core routers, or the ISP’s intranet provider border routers.
“Internet backbone:” The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks. See default-free zone (DFZ). The major ISPs’ system routers make up what could be considered to be the current Internet backbone core. ISPs operate all four types of the BGP routers described here. An ISP “core” router is used to interconnect its edge and border routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching protocols.
Port forwarding: Routers are also used for port forwarding between private Internet-connected servers.
Voice/Data/Fax/Video Processing Routers: Commonly referred to as access servers or gateways, these devices are used to route and process voice, data, video and fax traffic on the Internet. Since 2005, most long-distance phone calls have been processed as IP traffic (VOIP) through a voice gateway. Use of access server type routers expanded with the advent of the Internet, first with dial-up access and another resurgence with voice phone service.
Larger networks commonly use multilayer switches, with layer 3 devices being used to simply interconnect multiple subnets within the same security zone, and higher layer switches when filtering, translation, load balancing or other higher level functions are required, especially between zones.
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