1 Basic network tools Layers recap Basic Addressing ping traceroute ipconfig

2 Network Layers Telnet www … IP TCP UDP DNS SNMP TFTP …. ICMP IGMP PING TRACE … MCAST apps TCP/IP stack APPLICATION PRESENTATION SESSION TRANSPORT NETWORK DATA-LINK PHYSICAL OSI (ISO) Αρχή αδιαφάνειας Το κάθε επίπεδο «παρέχει υπηρεσίες» στο ανώτερο επίπεδο, κρύβοντάς του τις σχετικές λεπτομέρειες. FDDIEthernet802.11ATM

3 Network Layers APPLICATIONPRESENTATIONSESSIONTRANSPORTNETWORKDATA-LINKPHYSICAL Host A APPLICATIONPRESENTATIONSESSIONTRANSPORTNETWORKDATA-LINKPHYSICAL Host B

4 Headers Το κάθε επίπεδο  Παραλαμβάνει από το ανώτερο επίπεδο ένα πακέτο πληροφορίας  Προσθέτει πληροφορίες που απαιτούνται για να εκτελέσει τα «καθήκοντά» του  Παραδίδει το νέο επαυξημένο πακέτο πληροφορίας στο κατώτερο επίπεδοκαι  Παραλαμβάνει από το κατώτερο επίπεδο ένα πακέτο πληροφορίας  Επεξεργάζεται και αφαιρεί τις πληροφορίες που το αφορούν  Παραδίδει το υπόλοιπο του πακέτου στο ανώτερο επίπεδο Παράδειγμα: ένα ethernet frame… Κεφαλίδα Ethernet Ουρά Ethernet Κεφαλίδα IP Κεφαλίδα TCP Δεδομένα Εφαρμογής IP packet Διάφορα «πεδία» σε κάθε κεφαλίδα (header). Τα σημαντικότερα: Source & Destination addresses

5 Addresses APPLICATION PRESENTATION SESSION NETWORK DATA-LINK PHYSICAL TRANSPORT Ε-mail addressesFTP addressesHTTP addressesTCP portsUDP portsIP addressesAppletalkIPΧ addressesMAC addresses

6 More Addresses MAC addresses: 6 bytes – ffff.ffff.ffff IP address: – netmask: – eg: IP: netmask: TCP / UDP port: 0 – 65535

7 Basic network tools ping traceroute ipconfig

8 ping – What is it? ping is a computer network tool used to test whether a particular host is reachable across an IP networkcomputer networkhostIP uses the ICMP protocol

9 Ping – How it works? Source host generates an ICMP datagram with source and destination IP addresses (ICMP ECHO datagram)ICMP Datagram is sent towards destination Each host that receives the IP datagram checks the destination address with its own address If there is not a match, the host forwards it If there is a match the destination host creates an ICMP ECHO REPLY and sends it back to source The host receives it, notes the time on the clock and finally prints PING output information, including the elapsed time

10 Round-Trip-Time (RTT): is the elapsed time it took to send the ICMP packet and to get the ICMP reply packet Time-To-Live (TTL): refers to how many routers(hops) your packet can go through before it expires. This is the TTL of the ICMP reply packet. This value is decremented by one at each hop on the way back.

11 traceroute – What is it? traceroute is a computer network tool which is used to trace the route of a packet through a TCP/IP network. uses the ICMP protocol

12 Traceroute – How it works? Source host sets the TTL for a packet to 1 Sends it towards destination When receiving “time exceeded” response (response when TTL=0), source host examines the packet to determine where the packet came from This identifies the machine one hop away Source host sets the TTL for a packet to 2 …

13 Three Round-Trip-Time measurements from respective router * means no response (probe lost, router not replying)

14 ipconfig– What is it? Ipconfig is a computer network tool for Windows (ifconfig is equivalent for unix) that displays all current TCP/IP network configuration values and refreshes Dynamic Host Configuration Protocol DHCP and Domain Name System DNS settings. [TCP/IPDHCPDNS [

15 Local Network Interface Information of Local Network Interface