CS/컴퓨터네트워크

[Ch5] ICMP, SDN, SNMP

호프 2024. 1. 1. 18:19

ICMP

ICMP (Internet Control Message Protocol)

ICMP: Internet Control Message Protocol

  • used by hosts & routers to communicate network-level information
    • error reporting
    • 중간 라우터에서 incoming pkt에 문제 발생 시, ICMP msg를 생성하여 해당 pkt의 src host로 전송한다.
  • network-layer above "IP": ICMP msgs carried in IP datagrams
  • ICMP mesageL type + code + first 8 bytes of IP datagram causing error
    • 최종적으로 해당 패킷을 만든 프로세스가 사용하는 포트 번호를 알려주기 위해
  • used for traceroute

SDN

NW control app(Routing + NAT, load balancing, firewall, accounting) is programmed as sophisticated SW using high-level API(north bound) at servers which are distinct and remote from [simple & fast] NW devices(packet switch) where the Internet user's traffic go through

SDN (Software Defined Network)

SDN
traditional router (embedded) -> SDN

 

SDN is a framework

  • to allow network administrators to automatically and dynamically manage and control
  • a large number of entwork devices, services, topology, traffic paths and packet handling (QoS) policies
  • using high-level languages and APIs
  • multi-tenant environment: SDN controlled NW device

SDN structure

  • physical separation of control plane and data plane
  • logically centralized control plane(server) controls several routers
    • for easier network management, programmable router, open(non-proprietary) implementation of control plane

 

  • 물리적으로는 가입자 패킷이 지나다니는 네트워크 장비의 물리적 분포를 고려해 위치하는 여러 개의 서버들이 logically 하게는 한 개 처럼 동작
  • SDN에서 라우팅 프로토콜은 SDN Controller에서 동작한다? (X) 👉 라우팅 프로토콜을 포함한 다양한 middle box 기능들은 최상의 network control app에 해당한다. SDN Controller는 실제 가입자 패킷이 지나다니는 HW 장비의 자원을 관리하여 상위 app에 알려주는 역할을 한다.

 

SDN: Data plane switches

  • fast, simple, commodity switches implementing generalized data-plane forwarding in hardware
  • southbound API (e.g. OpenFlow) for communicating with controller
  • switch flow table computed by controller

SDN: Network control applications

  • brains of control: implement control functions using northbound API provided by SDN controller
  • can be provided by 3rd party: distinct from SDN controller
  • routing protocol을 포함한 다양한 middle box 기능들을 수행

SDN: SDN Controller (Network OS)

  • maintain network state information (switch가 알려줌) -> 상위 application에 전달
  • interacts with network control applications via northbound API
  • interacts with network switches via southbound API
  • implemented as distributed system

 

  • SDN은 least-cost path 외에 운영자가 원하는 특정한 e2e path 설정 가능
  • flow table은 northbound 위의 app에서 SDN Controller 로부터 정보를 받아서 생성, 변경된다.

 

OpenFlow

OpenFlow protocol

  • operates btw controller and switch (southbound API)
  • using TCP to exchange messages
  • three classes of OpenFlow messages
    • controller-to-switch
    • switch-to-controller
    • symmetric

OpenFlow: controller-to-switch msg

  • feature: controller queries switch featrues, switch replies
  • configure: controller queries/sets switch configuration parameters
  • modify-state: add, delete, modify flow entries in the OpenFlow tables
  • packet-out: controller can send this packet out of specific switch port

OpenFlow: switch-to-controller msg

  • packet-in: transfer packet to controller
  • flow-removed: flow table entry deleted at switch
  • port status: infrom controller of a change in port status

SDN Controller(network operator) don't program switches by creating/sending OpenFlow msgs directly

👉 Instead, use higher-level abstraction (northbound API) at controller == Network control applications

 

NFV (Network Function Virtualization)

SDN

  • Internet-scaling: SDN은 scalability의 challenge가 있어 특정 목적을 가진 망에 적합함
    • reliable distributed system for control plane
    • networks, protocols meeting mission-specific requirements: real-time, ultra-reliable, ultra-secure ..

NFV (Network Function Virtualization)

  • destination-based forwarding에 기반한 라우팅 기능을 virtualization하는 것이므로 SDN 처럼 다양한 path 설정은 불가능하다.
  • separation of HW and function

SNMP

SNMP (Simple Network Management Protocol)

Network Management

  • requiring monitoring, control
  • deployment, integration, coordination of the HW, SW, and human elements

Infrastructure for Network management

  • managing server
  • managing device
  • MIB (Management Information Base)
  • network management protocol (= SNMP)
  • managed devices contain managed objects whose data is gathered into a MIB

SNMP는 네트워크 장비를 관리, 제어하기 위해 관리 서버와 관리 대상 agent 간에 주고받는 프로토콜로, 정기적으로 간단한 정보를 교환하는 방식이므로 초기 연결 지연이 없는 UDP를 사용한다.

 

SNMPv2 (RFC 3415) protocol

  • Application-layer (L5) protocol on UDP (ports 161, 162)
    • to convey network-management control and information msgs
    • btw a managing server and an agent
  • Two ways to convey MIB info, commands
    1. request/response mode
    2. trap mode

Chapter 5 Summary

  • Approaches to network control plane
    • per-router control (traditional)
    • logically centralized control (SDN; software defined networking)
  • Traditional routing algorithms
    • implementatino in Internet: RIP, OSPF, BGP
  • ICMP (Internet Control Message Protocol)
  • SDN controllers
  • SNMP (Simple Network Management Protocol)
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