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Understanding Classical IP over ATM: CLIP Model Overview

This chapter delves into Classical IP over ATM (CLIP) basics including functions, format, and comparison with Ethernet. Explore CLIP operation, LIS concepts, encapsulation, and the role of ATMARP server. Enhance your knowledge of running IP over ATM networks.

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Understanding Classical IP over ATM: CLIP Model Overview

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  1. Chapter Objectives After completing this chapter you will be able to: • Describe Classical IP over ATM (CLIP) • Describe the function of an ATMARP server • Define a logical IP subnet (LIS) • Describe the format of an ATMARP packet

  2. Classical IP over ATM (CLIP) • CLIP was the earliest model proposed for running IP over ATM (1993) • CLIP is a combination of IETF RFC 1577, Classical IP and ARP over ATM and RFC 1483, Multiprotocol Encapsulation over AAL5 • CLIP superimposes an IP network on top of ATM such that IP routing architecture remains unchanged

  3. 192.168.20.5 192.168.21.5 255.255.255.0 255.255.255.0 A B 192.168.20.5 192.168.21.5 255.255.255.0 255.255.255.0 Ethernet segment Ethernet segment 192.168.20.1 192.168.21.1 A B 255.255.255.0 255.255.255.0 Ethernet segment 192.168.20.1 192.168.21.1 255.255.255.0 ClassicalModel

  4. ClassicalModelAnalysis • Limitations of the classical model • Ignorance of underlying technology • Possible introduction of inefficiencies • CLIP vs Ethernet • CLIP operation similar to that of IP over Ethernet • Uses ATMARP to map IP addresses to ATM addresses • No ATM broadcast capability, so ATMARP server used • Why? • Familiarity - network administrators knew IP subnetting • Security - firewalls operate at an IP level

  5. 2 bytes 4 bytes 0 Hardware Type Protocol Type Operation Sender's hardware address length Sender's protocol address length Target's protocol address length Target's hardware address length Sender's ATM Address (20 bytes) Sender's Protocol Address Target ATM Address (20 bytes) Target Protocol Address ATMARP Packet Format

  6. ATM Network LIS 2 LIS 1 LIS 3 Logical IP Subnets (LISs)

  7. Encapsulation and MTU • LLC/SNAP encapsulation is used with CLIP by default • Used for IP and for all ATMARP messages • MTU is 9180 bytes • Inherited from SMDS specification for interoperability • MTU large enough to minimise IP fragmentation

  8. ATM ARP Server. Maintains a table of IP addresses mapped to corresponding ATM addresses ATMARP server issues an Inverse ATMARP when a connection is opened LIS Host replies with both it's ATM and IP addresses ATMARP Server

  9. B's ATM address? A B B's ATM address is ... Direct ATM connection CLIPOperation - SVCs

  10. A B B's IP address? PVC B's IP address is ... CLIPOperation - PVCs

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