Tunneling and Gateways Tunneling and Gateways Examples Gateways - PDF document

Topics Topics � Tunneling – Motivation – Terminology Tunneling and Gateways Tunneling and Gateways – Examples � Gateways – Motivation – Interoperability Srinidhi Varadarajan – Remote provisioning of functionality – Enhanced functionality – Security – Performance improvement Networking Reality Networking Reality Need for Tunneling and Gateways Need for Tunneling and Gateways Host Protocols � In a perfect networking world … TCP/IP – One set of network protocols would meet all Internet DECnet needs SNA – All systems would use this set of protocols Novell NetBEUI and no others Backbone … – When a new version is released, all systems would be instantly updated to use the new Networks Internet version IEEE 802.3 (Ethernet) Internet IEEE 802.5 (Token Ring) � But it is not a perfect world, so techniques IEEE 802.11 are needed to deal with “imperfections” FDDI – Gateways -- usually associated with ATM applications X.25 Frame Relay – Tunneling -- usually associated with lower … levels Interoperability (1) Interoperability (2) Interoperability (1) Interoperability (2) � Networks are not homogeneous � Keys to interoperability – Investment in existing equipment – Application program interfaces that – Transitions are not instantaneous support multiple underlying services, – Different protocols are optimal for different e.g. sockets situations – Protocol design for “extensibility” – Vendor support may vary or may lead to • Generic services to simplify support for new deployments that are not “technically” optimal applications � Interoperability is critical in real networks • Separation of functionality into different – How does Application A use the services of protocols Protocol X at one host and the services of • Support for transitions to new versions, e.g. Protocol Y at another host version numbers in fixed location in header – How does Protocol X interact with Protocol Y within the network? Application Layer 1

Terminology Encapsulation Terminology Encapsulation � Gateways: Provide some form of translation � Encapsulation is simply the use of a lower between protocols at the same level level protocol data units (e.g., IEEE 802.3 – Translate Protocol X protocol data units (PDUs) to frames) to carry higher layer protocol data Protocol Y protocol data units units (e.g, IP datagrams) � Tunneling: Use a service (at the same “level”) to carry another service Protocol X PDU Protocol X PDU – Use Protocol Y to carry Protocol X protocol data units � Encapsulation: Using a lower layer service � These terms are often used interchangeably and with different meanings Protocol A PDU Protocol A PDU Tunneling Gateways Tunneling Gateways � Tunneling uses an alternate protocol to � A gateway translates from one protocol to carry protocol data units of another another, e.g. from SMTP to cc:mail. protocol at the same level. Example: using IPV4 to carry IPv6 packets Gateway encapsulates “decapsulates” Protocol X Protocol Y Protocol X Protocol Y Protocol X Physical Layer Interoperability MAC Layer Interoperability (1) Physical Layer Interoperability MAC Layer Interoperability (1) � Different medium access control (MAC) � Different physical media dependent (PMD) protocols are also common protocols are common – IEEE 802.2 Logical Link Control (LLC) protocol � A translation is done, but the “gateway” is commonly used with most MAC protocols device is called a repeater or hub � Interoperability provided through – Translation -- supports communication IEEE 802.3 10Base2 between Protocol X host and Protocol Y host (Thinwire Ethernet) – Encapsulation -- end points must both use Protocol X, but can travel over an intermediate Protocol Y network Hub IEEE 802.3 10BaseT � Example (Twisted-pair Ethernet) – IEEE 802.3 (Ethernet) – Fiber Distributed Data Interface (FDDI) Application Layer 2

MAC Layer Interoperability (2) MAC Layer Interoperability (3) MAC Layer Interoperability (2) MAC Layer Interoperability (3) IEEE 802.3 IEEE 802.3 10Base2 10Base2 Encapsulating Encapsulating FDDI Transparent Bridge Bridge Bridge FDDI IEEE 802.3 FDDI IEEE 802.3 FDDI IEEE 802.3 PDU PDU PDU PDU PDU Network Layer Interoperability (1) Network Layer Interoperability (1) Network Layer Interoperability (2) Network Layer Interoperability (2) � Network layer interoperability is needed � 6Bone supports IPv6 connectivity across for IPv4 networks – Transition between versions, e.g. IPv4 to IPv6 IPv6 IPv6 IPv6 – Enhanced functionality, e.g. multicast services provided by the Multicast Backbone (MBONE) IPv4 PDU IPv6 IPv6 – Different routing protocols � Co-existence is related to interoperability IPv4 – Multiple network protocols, e.g. IPX and IP, can run over the same local area network, e.g. Ethernet Addressing – Multi-protocol routers can route different types � Manual configuration of network layer protocol data units IPv6 � Auto-configure Application Layer Interoperability (1) Application Layer Interoperability (2) Application Layer Interoperability (1) Application Layer Interoperability (2) � Different applications using different � Application gateway allows different protocols must also interact applications to interoperate � Gateways -- translate between different applications providing the same service Mail A (client) – Mail services using cc:Mail and SMTP (Simple Mail A/B Mail Transfer Protocol) Gateway � Tunneling -- allow the use of different a underlying network – UDP- or TCP-based applications over an IPX Mail B network (server) Application Layer 3

Application Layer Interoperability (3) Application Gateways Application Layer Interoperability (3) Application Gateways � Application-level tunneling allows an application � An application gateway relays information designed for Protocol X to operate over a network between a client and a desired service that supports only Protocol Y – Gateway, in this context, is a program – The host running the program may be referred to as a gateway Protocol X Protocol X Client Application Client Application � An edge router may also be referred to as Socket Simulation Socket Simulation a gateway (from a LAN to a WAN), but this Library Library is a different use of the term OS with support OS with support for Protocol Y for Protocol Y Net Y Uses of an Application Gateway Interoperability Uses of an Application Gateway Interoperability � Interoperability � Gateways can provide interoperability – Different applications providing similar service � Example of need: electronic mail – Different versions of the same service – Internet � Support for clients with limited • Simple Mail Transfer Protocol (SMTP) • Post Office Protocol (POP) functionality • Internet Message Access Protocol (IMAP) – Move complexity to the gateway – Historical � Enhanced services • BITNET – Extending the functionality of a given protocol • USENET � Security – Proprietary • cc:mail – Firewalls • MCI Mail � Enhance performance • others … – Implement caching at the gateway Mail Interoperability (1) Mail Interoperability (2) Mail Interoperability (1) Mail Interoperability (2) � Gateway allows mail to be � Mail gateway often associated Mail B exchanged between different types Server directly with a of clients and servers server Mail A � Gateway must deal with Gateway – Format – Content representation – Addressing Mail A Mail B Client Client Application Layer 4

Clients With Limited Functionality SMTP with POP or IMAP Clients With Limited Functionality SMTP with POP or IMAP � Clients may not need full functionality � SMTP is used to move mail through the Internet � POP or IMAP is a simpler client-server protocol – Complexity just for a mail access – Cost – Security – Ease-of-use (emphasis on user interface) POP3 IMAP SMTP SMTP � Clients may not be able to provide full Server Server functionality – Handheld devices IMAP POP3 Client Client Enhanced Services AT&T Wireless Internet Mail Gateway AT&T Wireless Internet Mail Gateway Enhanced Services � The functionality of a protocol can be � A gateway can be used to deliver mail to extended by a gateway very simple devices over a network other – Client uses Protocol X to access the gateway than the Internet – The gateway can then service client request using Protocol Y POP3 Mail � Common Gateway Interface (CGI) at a SMTP SMTP Server Gateway WWW server is an example of such an application gateway – Invokes a gateway program or script – CGI defines PCS Internet • Invocation mechanism Network POP3 • Reply mechanism Client Common Gateway Interface (1) Common Gateway Interface (2) Common Gateway Interface (1) Common Gateway Interface (2) � CGI operation (1) URL, param (2) CGI – Client uses HTTP to transfer request to server (3) Process – Server extracts request and invokes a gateway program (defined by CGI) Web HTTP Gateway Browser Server Program – Gateway program processes request, possibly accessing a remote service (5) HTML, text, … (4) HTML, text, … – Gateway program returns result to server (defined by CGI) – Server returns result to clients using HTTP Application Layer 5