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Netzwerkgrundlagen - Von Ethernet bis IP

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Was ist dieses Ethernet, was haben wir da für Geräte und warum? Was tun die? Was hat das mit Bäumen zu tun und wer ist dieses MAC?

Was ist eine IP-Adresse? Wie funktioniert Subnetting mit CIDR und was sind eigentlich diese Netzwerkklassen von denen immernoch Menschen reden? Was sind private und öffentliche IPs und wo bekomme ich die her? Wie konfiguriere ich das alles unter Linux? Was sind Routingtabellen und warum habe ich davon eigentlich mindestens drei Stück?

Dieser Vortrag gibt Antworten auf alle diese Fragen und noch einige mehr. Subnetting nach CIDR bildet die Grundlagen für Routing in heutigen IP-Netzwerken;
RFC1918, RFC3927 und RFC6598 definieren jeweils “private” IP-Bereich für interne Nutzung, für öffentliche IPs haben wir in Europa das RIPE. Eine Einführung in iproute2 zeigt, wie man all das unter Linux “zu Fuß” konfiguriert und wie man die Netzwerkkonfiguration am Beispiel von Debian reboot-save einrichtet.

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Netzwerkgrundlagen - Von Ethernet bis IP

  1. 1. Netzwerkgrundlagen - Von Ethernet bis IP FrOSCon 13 Network Track Falk Stern, Maximilian Wilhelm 1 / 33
  2. 2. Agenda 1. Who's who 2. Models 3. Ethernet 4. IPv4 5. Linux Hands-on 2 / 33
  3. 3. Who's who Falk Stern Full Stack Infrastructure Engineer IPv6 fanboy Runs his own Kubernetes cluster in his basement Consultant @ Profi Engineering Systems AG Contact @wrf42 falk@fourecks.de 3 / 33
  4. 4. Who's who Maximilian Wilhelm Networker OpenSource Hacker Fanboy of (Debian) Linux ifupdown2 Occupation: By day: Senior Infrastructure Architect, Uni Paderborn By night: Infrastructure Archmage, Freifunk Hochstift In between: Freelance Solution Architect for hire Contact @BarbarossaTM max@sdn.clinic 4 / 33
  5. 5. Who's who Models Layer models - ISO/OSI, TCP/IP & Hybrid 5 / 33
  6. 6. Who's who Models Layer models - ISO/OSI, TCP/IP & Hybrid Physical Wires, Wireless - 802.3 & 802.11 (Bit) Data Link Addressing stations on the same physical medium (Ethernet MAC) (Frame) Network Adressing stations somewhere in the entire network (IPv4, IPv6) (Packet) Transport How to transport data? (Datagram, Segment) Session, Presentation, Application Which data to transport? (SSH, IRC, HTTP, etc.) 6 / 33
  7. 7. Who's who Models Ethernet Ethernet 7 / 33
  8. 8. Who's who Models Ethernet Hardware - What does it look like? Source: Wikimedia commons 8 / 33
  9. 9. Who's who Models Ethernet Ethernet Developed between 1973 and 1974 at Xerox Inspired by ALOHAnet, the Packet Radio Network on Hawaii At first available with 2,94 Mbps, 10 Mbps available commercially since 1980 Further development lead to IEEE standard 802.3 in 1983 CSMA/CD - "Carrier Sense, Multiple Access, Collision Detect" Ethernet today: Common access port speed: 1 Gbit/s Common uplink/server interfaces speed: 10 - 40 Gbit/s Up to 400-Gbit/s available commercially Interfaces for copper or multi-mode / single-mode fiber Preamble SFD Source MAC Address Destination MAC Address EtherType FCSPayload Source: Wikimedia Commons 9 / 33
  10. 10. Who's who Models Ethernet Ethernet Technology Repeater Maximum Segmentlength in on network segment around 100m Repeater amplify and repeat signals Extend broadcast domains Extend collision domains Bridges Extend broadcast domains Limit collision domains Important Rule: Frames must not be send out on port where they were received 10 / 33
  11. 11. Who's who Models Ethernet Ethernet Devices Hubs Repeater with many ports Switches Bridges with many ports Three possible actions to happen with any frame: Forward Replicate Drop 11 / 33
  12. 12. Who's who Models Ethernet Addresses Format: AA:BB:CC:DD:EE:FF Identify stations on the same physical medium Should to unique (on the medium) 1st octet 2nd octet 3rd octet 4th octet 5th octet 6th octet 6 octets or Organisationally Unique Identifier (OUI) Network Interface Controller (NIC) Specific 3 octets 3 octets b7 b6 b5 b4 b3 b2 b1 b0 8 bits 0: 1: unicast multicast 0: 1: globally unique (OUI enforced) locally administered Source: Wikipedia Commons 12 / 33
  13. 13. Who's who Models Ethernet Linux command line example $ ip link show 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: enp0s25: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000 link/ether 70:5a:0f:cf:21:f3 brd ff:ff:ff:ff:ff:ff 3: wlo1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000 link/ether 64:80:99:cf:66:6f brd ff:ff:ff:ff:ff:ff 13 / 33
  14. 14. Who's who Models Ethernet Spanning Tree Protocol for loop prevention within ethernet networks Create logical tree of network topology based on BPDUs Will block connections which will produce loops Only deactivate STP if you really know better Seriously! 14 / 33
  15. 15. Who's who Models Ethernet IPv4 15 / 33
  16. 16. Who's who Models Ethernet IPv4 IPv4 Adresses Identify stations within and beyond subnets Up to - but not limited to - the Internet 32bit long Composed of 4 octets 127.0.0.1 94.45.240.1 Subdived into network and host part What is now known as the Internet started as a research project in the 1970s to design and develop a set of protocols that could be used with many different network technologies to provide a seamless, end- to-end facility for interconnecting a diverse set of end systems. Source: RFC4632, Section 2 16 / 33
  17. 17. Who's who Models Ethernet IPv4 Network Classes (historical!) Deprecated since 1993 (RFC1519)!!1! Long live CIDR / VLSM Correct and complete definition given for historical attribution only! DO NOT USE IN REAL LIFE ANYMORE! SRSLY! Class Binary Prefix IP Space Default Mask A 0... 0.0.0.0 - 127.255.255.255 /8 B 10.. 128.0.0.0 - 191.255.255.255 /16 C 11.. 192.0.0.0 - 223.255.255.255 /24 D 1110 224.0.0.0 - 239.255.255.255 E 1111 240.0.0.0 - 255.255.255.255 17 / 33
  18. 18. Who's who Models Ethernet IPv4 Subnetting - CIDR / VLSM Classless InterDomain Routing Variable Length Subnet Mask Introduced in 1993, RFC4632 (original RFC1519) Prefix Notation -> Number of bits in network part of address 255.255.255.0 == 24 Bit netmask == /24 18 / 33
  19. 19. Who's who Models Ethernet IPv4 Pre xes to know/ Private stu Loopback 127.0.0.0/8 RFC1918 - Private Address Space 10.0.0.0/8, 172.16.0.0/12 und 192.168.0.0/16 RFC3927 - APIPA / Link-Local 169.254.0.0/16 RFC6598 - Shared Address Space (CGN) 100.64.0.0/10 RFC5737 - Documentation prefixes 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24 RFC8190 - Special-Purpose IP Address Registries Complete list of special prefixes 19 / 33
  20. 20. Who's who Models Ethernet IPv4 ARP - Address Resolution Protocol Glue between Ethernet and IP Simple protocol to resolve MAC address of IP peer Two messages types who-has is-at A B ARP WHO-HAS 192.168.1.1 192.168.1.1 IS-AT C0:FF:EE:BA:BE:01 A B 20 / 33
  21. 21. Who's who Models Ethernet IPv4 Routing Every device speaking IP has a routing table German translation according to IBM: "Leitwegtabelle" Packets are forwarded according to longest prefix match Default Gateway or Gateway of last resort used if no entry matches Hot Potato principle Packets forwarded to next hop w/o knowledge of their routing table Asymmetric routing Path to destination and return path don't have to be identical Routing table of your laptop right now: Prefix Iface / Next Hop 94.45.240.0/20 wlan0 0.0.0.0/0 94.45.240.1 21 / 33
  22. 22. Who's who Models Ethernet IPv4 Source Address Selection With every routing decision for a locally originated connection a source address is selected based on the routing table. Usually the (primary) IP configured on the outgoing interface May be explicitly set to any IP For example IP on loopback interface Prefix Iface / Next Hop Src Address 94.45.240.0/20 wlan0 94.45.242.23 192.168.0.0/24 eth0 192.168.0.42 0.0.0.0/0 94.45.240.1 22 / 33
  23. 23. Who's who Models Ethernet IPv4 MTU/MSS Maximum Transmission Unit Maximum size of a frame Usually 1500 Bytes in Ethernet networks Usually >= 9000 Bytes in service provider backbones (Jumbo Frames) Maximum Segment Size Maximum size of a segment which fits into a TCP packet MTU - 60 Bytes 23 / 33
  24. 24. Who's who Models Ethernet IPv4 Where to get IP addresses? 24 / 33
  25. 25. Who's who Models Ethernet IPv4 IP delegation hierarchy Source: Obtaining IPv4 - Andrew de la Haye - RIPE Regional Meeting 2014 25 / 33
  26. 26. Who's who Models Ethernet IPv4 Linux Network con guration on Linux 26 / 33
  27. 27. Who's who Models Ethernet IPv4 Linux Network con guration on Linux R.I.P. ifconfig R.I.P. route R.I.P. arp R.I.P. vlan R.I.P. brctl R.I.P. tunctl <Moment of Silence/> Long live iproute2 27 / 33
  28. 28. Who's who Models Ethernet IPv4 Linux iproute - Networkers Swiss Army Nife Functions segregated into sub commands Lazy admin friendly: Commands can be shortend ip link Layer2 configuration Vlans Bridges ip addr Layer3 configuration / IP addresses ip route Routing ip neigh ARP / ND 28 / 33
  29. 29. Who's who Models Ethernet IPv4 Linux ip link ip link set { DEVICE | dev DEVICE } [ { up | down } ] [ promisc { on | off } ] [ name NEWNAME ] [ address LLADDR ] [ mtu MTU ] [ master DEVICE ] [ nomaster ] [...] ip link show [ DEVICE ] 29 / 33
  30. 30. Who's who Models Ethernet IPv4 Linux ip addr Usage: ip addr {add|change|replace} IFADDR dev STRING [ LIFETIME ] [...] ip addr del IFADDR dev STRING ip addr {show|flush} [ dev STRING ] [ scope SCOPE-ID ] [ to PREFIX ] [ FLAG-LIST ] [ label PATTERN ] IFADDR := PREFIX | ADDR peer PREFIX [ broadcast ADDR ] [ anycast ADDR ] [ label STRING ] [ scope SCOPE-ID ] SCOPE-ID := [ host | link | global | NUMBER ] [...] 30 / 33
  31. 31. Who's who Models Ethernet IPv4 Linux ip route Usage: ip route { list | flush } SELECTOR ip route { add | del | change | append | replace } ROUTE SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table TABLE_ID ] [ proto RTPROTO ] [ type TYPE ] [ scope SCOPE ] ROUTE := NODE_SPEC [ INFO_SPEC ] NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ] [ table TABLE_ID ] [ proto RTPROTO ] [ metric METRIC ] INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ]... NH := [ via ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS [...] 31 / 33
  32. 32. Who's who Models Ethernet IPv4 Linux ip neigh Usage: ip neigh { add | del | change | replace } { ADDR [ lladdr LLADDR ] [ nud STATE ] | proxy ADDR } [ dev DEV ] ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ] [ vrf NAME ] STATE := { permanent | noarp | stale | reachable | none | incomplete | delay | probe | failed } 32 / 33
  33. 33. Who's who Models Ethernet IPv4 Linux Questions Questions? 33 / 33

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