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For pure Internet Protocol (IP) forwarding function, a router is designed to minimize the state information associated with individual packets. The main purpose of a router is to connect multiple networks and forward packets destined either for its own networks or other networks. A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. This process is known as routing. When each router receives a packet, it searches its routing table to find the best match between the destination IP address of the packet and one of the network addresses in the routing table. Once a match is found, the packet is encapsulated in the Layer 2 data link frame for that outgoing interface. A router does not look into the actual data contents that the packet carries, but only at the layer 3 addresses to make a forwarding decision, plus optionally other information in the header for hint on, for example, QoS. Once a packet is forwarded, the router does not retain any historical information about the packet, but the forwarding action can be collected into the statistical data, if so configured. Forwarding decisions can involve decisions at layers other than layer 3. A function that forwards based on layer 2 information, is properly called a bridge. This function is referred to as layer 2 bridging, as the addresses it uses to forward the traffic are layer 2 addresses (e.g. MAC addresses on Ethernet). Besides making decision as which interface a packet is forwarded to, which is handled primarily via the routing table, a router also has to manage congestion, when packets arrive at a rate higher than the router can process. Three policies commonly used in the Internet are tail drop, random early detection (RED), and weighted random early detection (WRED). Tail drop is the simplest and most easily implemented; the router simply drops packets once the length of the queue exceeds the size of the buffers in the router. RED probabilistically drops datagrams early when the queue exceeds a pre-configured portion of the buffer, until a pre-determined max, when it becomes tail drop. WRED requires a weight on the average queue size to act upon when the traffic is about to exceed the pre-configured size, so that short bursts will not trigger random drops. Another function a router performs is to decide which packet should be processed first when multiple queues exist. This is managed through quality of service (QoS), which is critical when Voice over IP is deployed, so that delays between packets do not exceed 150ms to maintain the quality of voice conversations. Yet another function a router performs is called policy-based routing where special rules are constructed to override the rules derived from the routing table when a packet forwarding decision is made. These functions may be performed through the same internal paths that the packets travel inside the router. Some of the functions may be performed through an application-specific integrated circuit (ASIC) to avoid overhead caused by multiple CPU cycles, and others may have to be performed through the CPU as these packets need special attention that cannot be handled by an ASIC.
Article Result :
For authentic Internet Protocol (IP) forwarding function, a router is advised to abbreviate the accompaniment advice associated with alone packets. The capital purpose of a router is to affix assorted networks and advanced packets destined either for its own networks or added networks. A router is advised a Band 3 accessory because its primary forwarding accommodation is based on the advice in the Band 3 IP packet, accurately the destination IP address. This activity is accepted as routing. Back anniversary router receives a packet, it searches its acquisition table to acquisition the best bout amid the destination IP abode of the packet and one of the arrangement addresses in the acquisition table. Already a bout is found, the packet is encapsulated in the Band 2 abstracts articulation anatomy for that approachable interface. A router does not attending into the absolute abstracts capacity that the packet carries, but alone at the band 3 addresses to accomplish a forwarding decision, additional optionally added advice in the attack for adumbration on, for example, QoS. Already a packet is forwarded, the router does not absorb any actual advice about the packet, but the forwarding activity can be calm into the statistical data, if so configured.
Forwarding decisions can absorb decisions at layers added than band 3. A activity that assiduously based on band 2 information, is appropriately alleged a bridge. This activity is referred to as band 2 bridging, as the addresses it uses to advanced the cartage are band 2 addresses (e.g. MAC addresses on Ethernet).
Besides authoritative accommodation as which interface a packet is forwarded to, which is handled primarily via the acquisition table, a router additionally has to administer congestion, back packets access at a amount college than the router can process. Three behavior frequently acclimated in the Internet are appendage drop, accidental aboriginal apprehension (RED), and abounding accidental aboriginal apprehension (WRED). Appendage bead is the simplest and best calmly implemented; the router artlessly drops packets already the breadth of the chain exceeds the admeasurement of the buffers in the router. RED probabilistically drops datagrams aboriginal back the chain exceeds a pre-configured allocation of the buffer, until a pre-determined max, back it becomes appendage drop. WRED requires a weight on the boilerplate chain admeasurement to act aloft back the cartage is about to beat the pre-configured size, so that abbreviate bursts will not activate accidental drops.
Another activity a router performs is to adjudge which packet should be candy aboriginal back assorted queues exist. This is managed through affection of account (QoS), which is analytical back Articulation over IP is deployed, so that delays amid packets do not beat 150ms to advance the affection of articulation conversations.
Yet addition activity a router performs is alleged policy-based acquisition area appropriate rules are complete to override the rules acquired from the acquisition table back a packet forwarding accommodation is made.
These functions may be performed through the aforementioned centralized paths that the packets biking central the router. Some of the functions may be performed through an application-specific chip ambit (ASIC) to abstain aerial acquired by assorted CPU cycles, and others may accept to be performed through the CPU as these packets charge appropriate absorption that cannot be handled by an ASIC.
Enter Article
For pure Internet Protocol (IP) forwarding function, a router is designed to minimize the state information associated with individual packets. The main purpose of a router is to connect multiple networks and forward packets destined either for its own networks or other networks. A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. This process is known as routing. When each router receives a packet, it searches its routing table to find the best match between the destination IP address of the packet and one of the network addresses in the routing table. Once a match is found, the packet is encapsulated in the Layer 2 data link frame for that outgoing interface. A router does not look into the actual data contents that the packet carries, but only at the layer 3 addresses to make a forwarding decision, plus optionally other information in the header for hint on, for example, QoS. Once a packet is forwarded, the router does not retain any historical information about the packet, but the forwarding action can be collected into the statistical data, if so configured. Forwarding decisions can involve decisions at layers other than layer 3. A function that forwards based on layer 2 information, is properly called a bridge. This function is referred to as layer 2 bridging, as the addresses it uses to forward the traffic are layer 2 addresses (e.g. MAC addresses on Ethernet). Besides making decision as which interface a packet is forwarded to, which is handled primarily via the routing table, a router also has to manage congestion, when packets arrive at a rate higher than the router can process. Three policies commonly used in the Internet are tail drop, random early detection (RED), and weighted random early detection (WRED). Tail drop is the simplest and most easily implemented; the router simply drops packets once the length of the queue exceeds the size of the buffers in the router. RED probabilistically drops datagrams early when the queue exceeds a pre-configured portion of the buffer, until a pre-determined max, when it becomes tail drop. WRED requires a weight on the average queue size to act upon when the traffic is about to exceed the pre-configured size, so that short bursts will not trigger random drops. Another function a router performs is to decide which packet should be processed first when multiple queues exist. This is managed through quality of service (QoS), which is critical when Voice over IP is deployed, so that delays between packets do not exceed 150ms to maintain the quality of voice conversations. Yet another function a router performs is called policy-based routing where special rules are constructed to override the rules derived from the routing table when a packet forwarding decision is made. These functions may be performed through the same internal paths that the packets travel inside the router. Some of the functions may be performed through an application-specific integrated circuit (ASIC) to avoid overhead caused by multiple CPU cycles, and others may have to be performed through the CPU as these packets need special attention that cannot be handled by an ASIC.
Article Result :
For authentic Internet Protocol (IP) forwarding function, a router is advised to abbreviate the accompaniment advice associated with alone packets. The capital purpose of a router is to affix assorted networks and advanced packets destined either for its own networks or added networks. A router is advised a Band 3 accessory because its primary forwarding accommodation is based on the advice in the Band 3 IP packet, accurately the destination IP address. This activity is accepted as routing. Back anniversary router receives a packet, it searches its acquisition table to acquisition the best bout amid the destination IP abode of the packet and one of the arrangement addresses in the acquisition table. Already a bout is found, the packet is encapsulated in the Band 2 abstracts articulation anatomy for that approachable interface. A router does not attending into the absolute abstracts capacity that the packet carries, but alone at the band 3 addresses to accomplish a forwarding decision, additional optionally added advice in the attack for adumbration on, for example, QoS. Already a packet is forwarded, the router does not absorb any actual advice about the packet, but the forwarding activity can be calm into the statistical data, if so configured.
Forwarding decisions can absorb decisions at layers added than band 3. A activity that assiduously based on band 2 information, is appropriately alleged a bridge. This activity is referred to as band 2 bridging, as the addresses it uses to advanced the cartage are band 2 addresses (e.g. MAC addresses on Ethernet).
Besides authoritative accommodation as which interface a packet is forwarded to, which is handled primarily via the acquisition table, a router additionally has to administer congestion, back packets access at a amount college than the router can process. Three behavior frequently acclimated in the Internet are appendage drop, accidental aboriginal apprehension (RED), and abounding accidental aboriginal apprehension (WRED). Appendage bead is the simplest and best calmly implemented; the router artlessly drops packets already the breadth of the chain exceeds the admeasurement of the buffers in the router. RED probabilistically drops datagrams aboriginal back the chain exceeds a pre-configured allocation of the buffer, until a pre-determined max, back it becomes appendage drop. WRED requires a weight on the boilerplate chain admeasurement to act aloft back the cartage is about to beat the pre-configured size, so that abbreviate bursts will not activate accidental drops.
Another activity a router performs is to adjudge which packet should be candy aboriginal back assorted queues exist. This is managed through affection of account (QoS), which is analytical back Articulation over IP is deployed, so that delays amid packets do not beat 150ms to advance the affection of articulation conversations.
Yet addition activity a router performs is alleged policy-based acquisition area appropriate rules are complete to override the rules acquired from the acquisition table back a packet forwarding accommodation is made.
These functions may be performed through the aforementioned centralized paths that the packets biking central the router. Some of the functions may be performed through an application-specific chip ambit (ASIC) to abstain aerial acquired by assorted CPU cycles, and others may accept to be performed through the CPU as these packets charge appropriate absorption that cannot be handled by an ASIC.
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