4: Network Layer 4a-1 13: IPV6 and NAT Last Modified: 10/30/2015 4:46:44 AM Adapted from Gordon Chaffee’s slides

4: Network Layer 4a-2 IPv6

4: Network Layer 4a-3 History of IPv6 r IETF began thinking about the problem of running out of IP addresses in 1991 r Requires changing IP packet format - HUGE deal! r While we’re at it, lets change X too r “NGTrans” (IPv6 Transition) Working Group of IETF - June 1996

4: Network Layer 4a-4 IPv6 Wish List r From “The Case for IPv6” r Scalable Addressing and Routing r Support for Real Time Services r Support of Autoconfiguration (get your own IP address and domain name to minimize administration r Security Support r Enhanced support for routing to mobile hosts

4: Network Layer 4a-5 IPv4 Datagram VersionHLen TOSLength IdentFlagsOffset TTLProtocolChecksum SourceAddr DestinationAddr Options (variable) Pad (variable) Data

4: Network Layer 4a-6 IPv6 Datagram VersionTrafficClassFlowLabel PayloadLenNextHeaderHopLimit SourceAddress DestinationAddress Next header/data

4: Network Layer 4a-7 IPv6 Base Header Format r VERS = IPv6 r TRAFFIC CLASS: specifies the routing priority or QoS requests r FLOW LABEL: to be used by applications requesting performance guarantees r PAYLOAD LENGTH: like IPv4’s datagram length, but doesn’t include the header length like IPv4 r NEXT HEADER: indicates the type of the next object in the datagram either type of extension header or type of data r HOP LIMIT: like IPv4’s TimeToLive field but named correctly r NO CHECKSUM (processing efficiency)

4: Network Layer 4a-8 Address Space r 32 bits versus 128 bits - implications? m 4 billiion vesus 3.4 X10 38 m 1500 addresses per square foot of the earth surface

4: Network Layer 4a-9 Addresses r Still divide address into prefix that designates network and suffix that designates host r But no set classes, boundary between suffix and prefix can fall anywhere (CIDR only) r Prefix length associated with each address

4: Network Layer 4a-10 Addresses Types r Unicast: delivered to a single computer r Multicast: delivered to each of a set of computers (can be anywhere) m Conferencing, subscribing to a broadcast r Anycast: delivered to one of a set of computers that share a common prefix m Deliver to one of a set of machines providing a common servicer

4: Network Layer 4a-11 Address Notation r Dotted sixteen? m r Colon hexadecimal notation (8 groups) m 69DC:8768:9A56:FFFF:0:5634:343 r Or even better with zero compression (replace run of all 0s with double ::) r Makes host names look even more attractive huh?

4: Network Layer 4a-12 Special addresses r Ipv4 addresses all reserved for compatibility m 96 zeros + IPv4 address = valid IPv6 address r Local Use Addresses m Special prefix which means “this needn’t be globally unique” m Allow just to be used locally m Aids in autoconfiguration

4: Network Layer 4a-13 Datagram Format r Base Header + 0 to N Extension Headers + Data Area

4: Network Layer 4a-14 Extensible Headers r Why? r Saves Space and Processing Time m Only have to allocate space for and spend time processing headers implementing features you need r Extensibility m When add new feature just add an extension header type - no change to existing headers m For experimental features, only sender and receiver need to understand new header

4: Network Layer 4a-15 Flow Label r Virtual circuit like behaviour over a datagram network r A sender can request the underlying network to establish a path with certain requirements Traffic class specifies the general requirements (ex. Delay < 100 msec.) r If the path can be established, the network returns an identifier that the sender places along with the traffic class in the flow label r Routers use this identifier to route the datagram along the prearranged path

4: Network Layer 4a-16 ICMPv6 r New version of ICMP r Additional message types, like “Packet Too Big” r Multicast group management functions

4: Network Layer 4a-17 Summary like IPv4 r Connectionless (each datagram contains destination address and is routed seperately) r Best Effort (possibility for virtual circuit behaviour) r Maximum hops field so can avoid datagrams circulating indefinitely

4: Network Layer 4a-18 Summary New Features r Bigger Address Space (128 bits/address) m CIDR only m Any cast addresses r New Header Format to help speed processing and forwarding m Checksum: removed entirely to reduce processing time at each hop m No fragmentation r Simple Base Header + Extension Headers m Options: allowed, but outside of header, indicated by “Next Header” field r Ability to influence the path a datagram will take through the network (Quality of service)

4: Network Layer 4a-19 Transition From IPv4 To IPv6 r Not all routers can be upgraded simultaneous m no “flag days” m How will the network operate with mixed IPv4 and IPv6 routers? r Two proposed approaches: m Dual Stack: some routers with dual stack (v6, v4) can “translate” between formats m Tunneling: IPv6 carried as payload n IPv4 datagram among IPv4 routers

4: Network Layer 4a-20 Dual Stack Approach

4: Network Layer 4a-21 Tunneling IPv6 inside IPv4 where needed

4: Network Layer 4a-22 More Recent History r First blocks of IPv6 addresses delegated to regional registries - July 1999 r ~ websites in the.com domain that can be reached via an IPv6 enhanced client via an IPv6 TCP connection r U.S. government agencies required to be IPv6 compliant to meet an OMB mandate announced in 2005 r 2009/10 – Major websites like Google and Facebook on IPv6 r Info from Akamai’s State of the Internet report

4: Network Layer 4a-23 IPv5? r New version of IP temporarily named “IP - The Next Generation” or IPng r Many competing proposals; name Ipng became ambiguous r Once specific protocol designed needed a name to distinguish it from other proposals r IPv5 has been assigned to an experimental protocol ST

4: Network Layer 4a-24 Network Address Translation (NAT)

4: Network Layer 4a-25 Background r RFC 1918 defines private intranet address ranges for IPv4 m (Class A) m (Class B) m (Class C) r Addresses reused by many organizations r Addresses cannot be used for communication on Internet

4: Network Layer 4a-26 Problem Discussion r Hosts on private IP networks need to access public Internet r All traffic travels through a gateway to/from public Internet r Traffic needs to use IP address of gateway r Conserves IPv4 address space m Private IP addresses mapped into fewer public IP addresses

4: Network Layer 4a-27 Scenario Gateway Host A BMRC Server All Private Network hosts must use the gateway IP address Private Network Public Internet Public network IP address, globally unique Same private network IP addresses may be used by many organizations

4: Network Layer 4a-28 Network Address Translation Solution r Special function on gateway m IP source and destination addresses are translated m Internal hosts need no changes r TCP based protocols work well r Non-TCP based protocols more difficult r Changes required to applications that embed IP addresses? FTP? Others? r Provides some security m Hosts behind gateway difficult to reach m Possibly vulnerable to IP level attacks

4: Network Layer 4a-29 TCP NAT Example Server Internet NAT Gateway PROTO SADDR DADDR SPORT DPORT FLAGS CKSUM TCP SYN 0x NAT gateway sees SYN flag set, adds new entry to its translation table. It then rewrites the packet using gateway’s external IP address, Updates the packet checksum PROTO SADDR DADDR SPORT DPORT FLAGS CKSUM TCP SYN, ACK 0x Server responds to SYN packet with a SYN,ACK packet. The packet is sent to the NAT gateway’s IP address. Client Server IPAddr Port IPAddr Port NATPort NAT Translation Table PROTO SADDR DADDR SPORT DPORT FLAGS CKSUM TCP SYN 0x Host tries to connect to web server at It sends out a SYN packet using its internal IP address, PROTO SADDR DADDR SPORT DPORT FLAGS CKSUM TCP SYN, ACK 0x NAT gateway looks in its translation table, finds a match for the source and destination addresses and ports, and rewrites the packet using the internal IP address.

Network Layer 4-30 NAT traversal problem r client wants to connect to server with address m server address local to LAN (client can’t use it as destination addr) m only one externally visible NATed address: r solution 1: statically configure NAT to forward incoming connection requests at given port to server m e.g., ( , port 2500) always forwarded to port NAT router Client ?

Network Layer 4-31 NAT traversal problem r solution 2: Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol. Allows NATed host to:  learn public IP address ( )  add/remove port mappings (with lease times) i.e., automate static NAT port map configuration NAT router IGD

Network Layer 4-32 NAT traversal problem r solution 3: relaying (used in Skype) m NATed client establishes connection to relay m External client connects to relay m relay bridges packets between to connections Client NAT router 1. connection to relay initiated by NATed host 2. connection to relay initiated by client 3. relaying established

4: Network Layer 4a-33 Load Balancing Servers with NAT r Single IP address for web server r Redirects workload to multiple internal servers Server NAT Gateway (Virtual Server) Private Intranet Public Internet

4: Network Layer 4a-34 Load Balancing Networks with NAT NAT Gateway r Connections from Private Intranet split across Service Providers 1 and 2 r Load balances at connection level m Load balancing at IP level can cause low TCP throughput Private Intranet Service Provider 1 Service Provider 2 Network X

4: Network Layer 4a-35 NAT Discussion r NAT works best with TCP connections r NAT breaks End-to-End Principle by modifying packets r Problems m Connectionless UDP (Real Audio) m ICMP (Ping) m Multicast m Applications use IP addresses within data stream (FTP) r Need to watch/modify data packets

4: Network Layer 4a-36 Outtakes

4: Network Layer 4a-37 6Bone r The 6Bone: an IPv6 testbed r Started as a virtual network using IPv6 over IPv4 tunneling/encapsulation r Slowly migrated to native links for IPv6 transport r RFC 2471 r Abandoned 2006

4: Network Layer 4a-38 NAT Example NAT Gateway Server Address Translator TCP Connection 1

4: Network Layer 4a-39 TCP Protocol Diagram ClientServer SYN, ACK Packet 0:50 ACK 0:50 FIN FIN, ACK Source IP Address Destination IP Address Checksum Sequence Number Dest Port NumberSource Port Number TCP Header..... IP Header..... ACK SYN SYN flag indicates a new TCP connection