19531 - Telematics 8th Tutorial - IP, ARP, ICMP, DHCP & NAT Bastian Blywis Department of Mathematics and Computer Science Institute of Computer Science 16. December, 2010 Institute of Computer Science – Telematics Tutorial – 16. December, 2010 1 Outline 1. Network Components 2. End of the Ethernet Frame 3. LLC Classes 4. MTU 5. Network Components 6. Subnets 7. Internet Protocol Version 4 8. Checksum 9. Address Resolution Protocol 10. Self-Configuration 11. Tracing 12. Address Translation 13. ICMP Institute of Computer Science – Telematics Tutorial – 16. December, 2010 2 Network Components Name the function(-s) of the following network compo- nents: – Repeater – Hub – Switch – Bridge – Router – Gateway Which “data” do they handle and on which layer of the ISO/OSI reference model do they operate? Institute of Computer Science – Telematics Tutorial – 16. December, 2010 3 ? ? ? Network Components – Repeater – Receives a signal and retransmits it at a higher power (amplifies) – Dumb device, does not know and care about frames – Increases range of network – Layer 1 – Hub – Connects multiple stations together – Creates a network segment (bus topology) – Also called multi-port repeater – Dumb device, does not know and care about frames – Collisions can happen; single collision domain – Usually do not amplify signals – Layer 1 Institute of Computer Science – Telematics Tutorial – 16. December, 2010 4 Network Components – Switch – Connects multiple stations together – Connects network segments – Evaluates header of frames – Learns topology and limits broadcasts – Checks for frame errors – Several forwarding techniques, e.g., (virtual) cut-through – Layer 2 – Managed switches provide much more, e.g., telnet or web interface (and thus layer 3-7 services) – Bridge – Same as switch but connect different LANs – Usually behaves as defined in IEEE 802.1d – Bridges create different collision domains at their ports – Term often times synonymously used like switch – Layer 2 Institute of Computer Science – Telematics Tutorial – 16. December, 2010 5 Network Components – Router – Software and/or hardware for routing and forwarding data of packets (datagrams) – Connects logical subnets – Router knows output interface for each destination based on IP configuration of interfaces (usually also stored in routing table) or learned by routing protocol – Routing is often implemented in the application layer although it is a network layer service – Routers usually do not flood datagrams if output interface is unknown but use default route – Layer 3 – Gateway – “Protocol translator” – Several different definitions – Layer 4-7 (sometimes also includes lower layers) Note: Hardware routers usually also contain a switch/bridge Question: Are there actually layer 3 and layer 4 switches? Institute of Computer Science – Telematics Tutorial – 16. December, 2010 6 End of the Ethernet Frame – Compared to the IEEE 802.3 frame the Ethernet frame has no length but a type field. – How can a network interface card actually detect the end of the frame? Institute of Computer Science – Telematics Tutorial – 16. December, 2010 7 ? ? ? End of the Ethernet Frame – Frame end detection depends on particular host-to-network technology – Ethernet II: idle state detection of Manchester line code, no raising or falling edge for some specific time – Interframe gap (12 bytes = 9.6 µs in older Ethernet variants) – Alternative: Stop flag at the end of the frame (line signaling) – Alternative: Out-of-band signaling, separate clock line Institute of Computer Science – Telematics Tutorial – 16. December, 2010 8 LLC Classes – As discussed in the 5th tutorial, there are different Logical Link Control classes. – How do stations actually know which classes are supported by the others? Institute of Computer Science – Telematics Tutorial – 16. December, 2010 9 ? ? ? LLC Classes – All LLC implementations must support class 1 (unacknowledged, connection-less) – Required support of unnumbered format commands – Unnumbered information (UI) – eXchange IDentification (XID) – TEST link (TEST) – XID response contains supported LLC class/types (see page 52 in IEEE 802.2-1998) Institute of Computer Science – Telematics Tutorial – 16. December, 2010 10 MTU What is the Maximum Transfer Unit (MTU) and why is it relevant for bridging and routing? Institute of Computer Science – Telematics Tutorial – 16. December, 2010 11 ? ? ? MTU – MTU defines maximum size of payload in frame – Packets have to be fragmented if MTU is too low – Not all host-to-network technologies support fragmentation – IEEE 802.3 does not support fragmentation – IEEE 802.11 supports fragmentation to increase reliability – Packets will be dropped if fragmentation is not supported MTU Technology 1,5001 Ethernet 4,352 FDDI 4,464 IEEE 802.5 (4 Mbps) 17,914 IEEE 802.5 (16 Mbps) 2,312 IEEE 802.11 Table: Some MTU values 1MTU can actually be larger to enable VLANs and there are also so-called Jumbo frames Institute of Computer Science – Telematics Tutorial – 16. December, 2010 12 Network Components – Discuss the tasks of the network layer and how it differs from the lower and upper layers. – Name network layer protocols and their historical as well as current relevance. Institute of Computer Science – Telematics Tutorial – 16. December, 2010 13 ? ? ? Network Components Tasks of the network layer: – Data transmission over large distances, between heterogenous sub-networks – Addressing – Routing – Quality of Service (QoS) issues – Usually connection-less communication Institute of Computer Science – Telematics Tutorial – 16. December, 2010 14 Network Components – Layer 1-2 protocol for communication between adjacent hosts on LAN – Layer 1-2 protocol is specific for LAN ) protocol header is not preserved but replaced – Layer 3 protocol for communication between distant hosts – Layer 3 protocol supported by all nodes between source and destination ) protocol header is preserved and modified in network – Layer 4-7 protocols for communication between source and destination Layer 7 Layer 7 to to Layer 4 Layer 4 Layer 3 Layer 3 Layer 3 Layer 3 Layer 2 Layer 2 Layer 2 Layer 2 and and and and Layer 1 Layer 1 Layer 1 Layer 1 Source Router Router Destination But: much more complex today with tunneling, NAT, traffic shaping, load balancing, . Institute of Computer Science – Telematics Tutorial – 16. December, 2010 15 Network Components Network layer protocols: – DoD Standard Internet Protocol (IPv3) – Internetwork Packet Exchange (IPX), ISO/OSI – Datagram Delivery Protocol (DDP), AppleTalk – Internet Protocol Security (IPsec) – Internet Group Management Protocol (IGMP) – The swIPe IP Security Protocol (SwIPe) – ARP, ICMP, . Institute of Computer Science – Telematics Tutorial – 16. December, 2010 16 IPv4 Recapitulation – 32 bit addresses, but not 232 for unicast or routable – Four octets: A.B.C.D – Network and Host part, defined by subnet mark (deprecated) – Class-less Inter-Domain Routing (CIDR); format: 160.45.128.0/17 Information Sciences Institute University of Southern California Internet Protocol RFC 791, 1981 Institute of Computer Science – Telematics Tutorial – 16. December, 2010 17 IPv4 Recapitulation Address block Description Reference 0.0.0.0/8 Current network (only valid as source address) RFC 1700 10.0.0.0/8 Private network RFC 1918 14.0.0.0/8 Public data networks (reclaimed) RFC 1700 127.0.0.0/8 Loopback RFC 3330 128.0.0.0/16 Reserved RFC 3330 169.254.0.0/16 Link-Local RFC 3927 172.16.0.0/12 Private network RFC 1918 191.255.0.0/16 Reserved RFC 3330 192.0.0.0/24 Reserved RFC 3330 192.0.2.0/24 Documentation and example code (TEST-NET) RFC 3330 192.88.99.0/24 IPv6 to IPv4 relay RFC 3068 192.168.0.0/16 Private network RFC 1918 198.18.0.0/15 Network benchmark tests RFC 2544 223.255.255.0/24 Reserved RFC 3330 224.0.0.0/4 Multicasts (former Class D network) RFC 3171 240.0.0.0/4 Reserved (former Class E network) RFC 1700 255.255.255.255 Broadcast Table: Reserved IPv4 Address Blocks (excerpt) Institute of Computer Science – Telematics Tutorial – 16. December, 2010 18 IPv4 Recapitulation 0 4 8 16 19 31 Version IHL Diff. Service Total Length Identification Flags Fragment Offset Time to Live Protocol = 17 Header Checksum Source Destination Options Payload hhh hhh hhhh hhhh hhh hhh hhhh hhhh hhh hhh hhhh hhhh hhh hhh Figure: IPv4 Header Format with marked “problematic” fields Institute of Computer Science – Telematics Tutorial – 16. December, 2010 19 IPv4 Recapitulation Copy Class Option Length Description RFC 0 0 0 1 End of options list. RFC 791 0 0 1 1 NOP RFC 791 1 0 130 11 Security RFC 791, RFC 1108 1 0 131 variable Loose Source Route RFC 791 0 2 68 variable Time stamp RFC 781, RFC 791 1 0 133 3 to 31 Extended Security RFC 1108 1 0 134 Commercial Security 0 0 7 variable Record Route RFC 791 1 0 136 4 Stream Identifier RFC 791, RFC 1122 1 0 137 variable Strict Source Route RFC 791 0 0 10 Experimental Measurement 0 0 11 4 MTU Probe. (obsolete) RFC 1063, RFC 1191 0 0 12 4 MTU Reply. (obsolete) RFC 1063, RFC 1191 1 2 205 Experimental Flow Control 1 0 142 Expermental Access Control 0 0 15 ENCODE 1 0 144 IMI Traffic Descriptor 1 0 145 variable Extended Internet Protocol RFC 1385 0 2 82 12 Traceroute RFC 1393 1 0 147 10 Address Extension RFC 1475 1 0 148 4 Router Alert RFC 2113 1 0 149 6 to 38 Selective Directed Broadcast RFC 1770 Mode 1 0 150 Unassigned 1 0 151 Dynamic Packet State 1 0 152 Upstream Multicast Packet 0 0 25 QS, Quick-Start RFC 4782 0 0 30 EXP - RFC3692-style Experiment RFC 4727 0 2 94 EXP - RFC3692-style Experiment RFC 4727 1 0 158 EXP - RFC3692-style Experiment RFC 4727 1 2 222 EXP - RFC3692-style Experiment RFC 4727 Institute of Computer Science – Telematics Tutorial – 16. December, 2010Table: IPv4 Options 20 IPv4 Recapitulation IPv4 Issues: – Checksum only for header, usually layer 2 (e.g. Ethernet) and layer 4 (e.g.