Router internals
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The document discusses the internals of a router. It describes the main functions of a router which include basic forwarding, packet classification, routing processing, and management. It outlines the key components of a router including network interfaces, forwarding engine, queue manager, and traffic manager. It also explains the packet flow through different components of a router along the fast and slow paths.
Router internals
- 1. Router Internals Dr. Ramana I.I.T Rajasthan Dr. Ramana ( I.I.T Rajasthan ) Router Internals 1 / 8
- 2. Outline of the Lectures 1 Functions of a Router 2 Router Components 3 Packet Flow 4 Further Reading Dr. Ramana ( I.I.T Rajasthan ) Router Internals 2 / 8
- 3. Functions of a Router Router functions Basic forwarding functions IP Header validation Packet lifetime control Checksum recalculation Destination address lookup Fragmentation Handling IP options Complex forwarding functions Packet classification Packet translation Traffic prioritization Routing processing functions Handing routing updates Sending routing updates Router management (monitoring of various operations) Dr. Ramana ( I.I.T Rajasthan ) Router Internals 3 / 8
- 4. Functions of a Router (Cont.) Forwarding table Optimized for lookup a destination IP address against set of IP prefixes Could be implemented in hardware as lookup needs to be done for every packet Routing table Optimized for storing/updating network topology and calculating changes in network topology Implemented in software Dr. Ramana ( I.I.T Rajasthan ) Router Internals 4 / 8
- 5. Router Components Router Components Network interface - contains multiple ports which provide connectivity to various physical links (implements L2/L3 processing) Forwarding engine does lookup and determine outgoing interface packet classifying - to provide quality of services at the outgoing link Queue manager stores the packets in appropriate buffers at the outgoing port implements policies for dropping packets due to buffer overflows schedules packets depending on the packets priorities Traffic manager shapes outgoing traffic to meet service level agreements (SLAs) traffic policing to check the voilation of SLAs by the received traffic marking of traffic that has voilated the SLAs Backplane - shared/switched circuit through which packets are transfered between the incoming (ingress) and outgoing (egress) ports Dr. Ramana ( I.I.T Rajasthan ) Router Internals 5 / 8
- 6. Packet Flow Packet flow in a router Input Network Interface Forwarding Engine Buffer Buffer Backplane Queue Manager Traffic Manager Output Network Interface Router Control Processor Forwarding Table Routing Table 1 2 3 4 5 6 7 8 9 10 11 Control plane Data plane Dr. Ramana ( I.I.T Rajasthan ) Router Internals 6 / 8
- 7. Packet Flow Packet processing: Fast path and slow path Fast path (Data Path) Packet processed and transfered from ingress to egress network interfaces via backplane To achieve high speeds, operations are implemented in customized hardware Time-critical operation All basic and complex forwarding functions (except fragmentation and handling IP options) Slow path (Control path) Packets partially processed at the ingress interface and forwarded to CPU for further processing CPU directly forwards the packets to egress interface once it completes the processing Non time-critical operation Routing processing functions Processing of data packets that lead to errors in the fast path and generation of ICMP packets Fragmentation and handling IP options and ARP packet processing Dr. Ramana ( I.I.T Rajasthan ) Router Internals 7 / 8
- 8. Further Reading Further Reading IP Router Architectures: An Overview - http://www.cs.virginia.edu/˜cs757/papers/awey99.pdf Study of Internet Router Architectures - http://home.iitj.ac.in/˜ramana/Study-of-Internet-Router- Architectures.pdf Dr. Ramana ( I.I.T Rajasthan ) Router Internals 8 / 8