Embedded Systems September 2000 Vol13_10

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The d ual-stack router on one end of the communication takes IPv6 pack- ets from th e sende r, e ncapsulates them within IPv4 packets, then for- wards the packets across the 1Pv4 Internet. Another dual-stack router on the other side receives the IPv4 pack- ets, extracts the 1Pv6 packets inside, and fo rwards the IPv6 packets to their proper destination. Configuring tunne ls can be a little tricky. To make life easier, the IETF draft, "IPv6 Tunnel Broker," describes a way to automatically manage tun- nels. A tunnel broke r is a dual-stack machine that creates, modifi es, or deletes tunnels fo r you. To dig a tun- nel, you simply give the tunnel broker tl1e fo llowing information: • The IPv4 address of the tunnel's cl ient side • A nickname to be used fo r the DNS registratio n of th e glo bal 1Pv6 addresses assigned to both sides of the tunn el • The clie nt function : standalone host o r router See the IETF draft or more details on how a tunnel broker wo rks.14 Communicating with 1Pv4 machines Several mecha ni sms have bee n defined by the IETF for 1Pv6 applica- tions to talk with IPv4 applications. See the referenced documents for mo re detailed information. SIITI5 The Stateless IP / ICMP Translation Algorithm (SliT) translates between IPv4 and IPv6 packet headers in sepa- rate translator "boxes" in the network. NAT-PTI6 A combination of Network Address Translation (NAT) and Protocol Translation (PT) can be used to pro- vide transpare nt routing. This does not mandate dual-stacks or special purpose routing requi rements on end nodes. TCP / UDP Relay17 This mechanism translates packets at the TCP layer. A transport relay trans- lator box sits between an 1Pv6-only node and an IPv4-only node, handling the protocol translation. DSTMIS The Dual Stack Transition Mechanism (DSTM) provides a method to assign temporary global IPv4 addresses to IPv6 nodes. It also uses dynamic nm- nels within an IPv6 network to carry IPv4 traffic. 6to419 This mechanism uses an IPv4 network www 104 SEPTEMBER 2000 Embedded Systems Programming

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