CS615 - Aspects of System Administration Slide 1 CS615 - Aspects of System Administration Networking I Department of Computer Science Stevens Institute of Technology Jan Schaumann jschauma@stevens.edu https://stevens.netmeister.org/615/ Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 2 Networking I Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 3 Team Missions https://www.us-cert.gov/ics/advisories/icsa-19-274-01 https://is.gd/soixLV https://is.gd/vSuYvF https://is.gd/qkXhe2 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 4 TCP Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 5 Networking I Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 6 Networking I Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 7 Networking I Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 8 Networking I $ sudo tcpdump -w /tmp/out port 80 & $ curl -s -I http://www.cs.stevens.edu/ >/dev/null $ fg ^C $ sudo tcpdump -r /tmp/out -n -XX -c 1 15:23:43.477095 IP 172.16.1.30.51525 > 155.246.56.11.80: Flags [S], seq 1016422373, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 86305166 ecr 0,sackOK,eo 0x0000: c4b3 01db afe2 8c85 9047 b4f6 0800 4500 .........G....E. 0x0010: 0040 0000 4000 4006 b988 ac10 011e 9bf6 .@..@.@......... 0x0020: 380b c945 0050 3c95 5fe5 0000 0000 b002 8..E.P<._....... 0x0030: ffff 6109 0000 0204 05b4 0103 0306 0101 ..a............. 0x0040: 080a 0524 e98e 0000 0000 0402 0000 ...$.......... Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 9 Networking I Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 10 Networking I Layers: 0x0000: c4b3 01db afe2 8c85 9047 b4f6 0800 4500 .........G....E. 0x0010: 0040 0000 4000 4006 b988 ac10 011e 9bf6 .@..@.@......... 0x0020: 380b c945 0050 3c95 5fe5 0000 0000 b002 8..E.P<._....... 0x0030: ffff 6109 0000 0204 05b4 0103 0306 0101 ..a............. 0x0040: 080a 0524 e98e 0000 0000 0402 0000 ...$.......... Link layer information; here: Ethernet Network layer information; here: IP Transport layer information; here: TCP Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 11 Networking I OSI Layer 2 / TCP/IP Layer 1: Ethernet information: 0x0000: c4b3 01db afe2 8c85 9047 b4f6 0800 4500 .........G....E. 0x0010: 0040 0000 4000 4006 b988 ac10 011e 9bf6 .@..@.@......... 0x0020: 380b c945 0050 3c95 5fe5 0000 0000 b002 8..E.P<._....... 0x0030: ffff 6109 0000 0204 05b4 0103 0306 0101 ..a............. 0x0040: 080a 0524 e98e 0000 0000 0402 0000 ...$.......... Destination address: c4:b3:01:db:af:e2 Source address: 8c:85:90:47:b4:f6 Type: IP (0800) IPv4 stuff TCP stuff $ ifconfig en0 | grep ether ether 8c:85:90:47:b4:f6 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 12 Networking I OSI Layer 3 / TCP/IP Layer 2: Internet Protocol: 0x0000: c4b3 01db afe2 8c85 9047 b4f6 0800 4500 .........G....E. 0x0010: 0040 0000 4000 4006 b988 ac10 011e 9bf6 .@..@.@......... 0x0020: 380b c945 0050 3c95 5fe5 0000 0000 b002 8..E.P<._....... 0x0030: ffff 6109 0000 0204 05b4 0103 0306 0101 ..a............. 0x0040: 080a 0524 e98e 0000 0000 0402 0000 ...$.......... Version 4 (0100) + Header Length 20 (0101) = 01000101 = 45 DSCP default (000000) + Not-ECN (00) = 00 Total length = 0040 = 64 Identification = 0000 Flags = Don’t Fragment (010) + Frag Offset (00000) = 4000 TTL= 40 = 64 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 13 Networking I OSI Layer 3 / TCP/IP Layer 2: Internet Protocol: 0x0000: c4b3 01db afe2 8c85 9013 73c1 0800 4510 ..........s...E. 0x0010: 0040 0000 4000 4006 b988 ac10 011e 9bf6 .@..@.@......... 0x0020: 380b c945 0050 3c95 5fe5 0000 0000 b002 8..E.P<._....... 0x0030: ffff 6109 0000 0204 05b4 0103 0306 0101 ..a............. 0x0040: 080a 0524 e98e 0000 0000 0402 0000 ...$.......... Protocol: TCP (6) 06 Header Checksum: 0xb988 Source Address: 172.16.1.30 (ac10 011e) Destination Address: 155.246.56.11 (9bf6 380b) TCP Stuff: c945 ... 0000 $ ifconfig en0 | grep "inet " inet 172.16.1.30 netmask 0xffffff00 broadcast 172.16.1.255 $ Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 14 IPv4 Basics 10011011111101100011100000001011 IPv4 addresses are 32-bit numbers. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 15 IPv4 Basics 10011011 11110110 00111000 00001011 Each IPv4 address consists of four octets. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 16 IPv4 Basics 10011011 11110110 00111000 00001011 155 . 246 . 56 . 11 9B F6 38 0B Each IPv4 address consists of four octets. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 17 IPv4 Basics 10011011 11110110 00111000 00001011 IPv4 addresses are divided into a network part and a host part . Hosts on the same network ( broadcast domain ) can talk to each other without the help of a router. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 18 IPv4 Basics 10011011 11110110 00111000 00001011 There are three different classes of IPv4 networks. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 19 IPv4 Basics 10011011 11110110 00111000 00001011 There are three different classes of IPv4 networks. Well, five, really. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 20 IPv4 Basics Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 21 Subnets 10011011 11110110 00111000 00001011 11111111 11111111 00000000 00000000 A netmask splits the IPv4 address into network and host parts. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 22 Subnets 10011011 11110110 00111000 00001011 11111111 11111111 11111111 00000000 A netmask splits the IPv4 address into network and host parts. Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 23 Subnets $ ipcalc -n 155.246.56.11/16 Address: 155.246.56.11 10011011.11110110. 00111000.00001011 Netmask: 255.255.0.0 = 16 11111111.11111111. 00000000.00000000 Wildcard: 0.0.255.255 00000000.00000000. 11111111.11111111 => Network: 155.246.0.0/16 10011011.11110110. 00000000.00000000 HostMin: 155.246.0.1 10011011.11110110. 00000000.00000001 HostMax: 155.246.255.254 10011011.11110110. 11111111.11111110 Broadcast: 155.246.255.255 10011011.11110110. 11111111.11111111 Hosts/Net: 65534 Class B Try also: sipcalc -a 155.246.56.11/16 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 24 Subnets $ ipcalc -n 155.246.56.11/24 Address: 155.246.56.11 10011011.11110110.00111000. 00001011 Netmask: 255.255.255.0 = 24 11111111.11111111.11111111. 00000000 Wildcard: 0.0.0.255 00000000.00000000.00000000. 11111111 => Network: 155.246.56.0/24 10011011.11110110.00111000. 00000000 HostMin: 155.246.56.1 10011011.11110110.00111000. 00000001 HostMax: 155.246.56.254 10011011.11110110.00111000. 11111110 Broadcast: 155.246.56.255 10011011.11110110.00111000. 11111111 Hosts/Net: 254 Class B Try also: sipcalc -a 155.246.56.11/24 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 25 CIDR cheat sheet A.B.C.D/N N = bits describing network portion of address M = 32 − N = bits in host portion of address 2 M = number of addresses on this subnet 2 M − 2 = number of possible hosts first address on subnet = network address last address on subnet = broadcast address subnet division need not occur on dotted boundary only for example, you can divide 155.246.89.0/24 into four /26 networks networks starting at .0, .64, .128, .192 Which of the following is not a valid netmask? 255.255.253.0, 255.255.250.0, 255.255.240.0 Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 26 Mommy, where do IP addresses come from? The Internet Assigned Numbers Authority (IANA) oversees global IP address/AS number allocation, root zone management etc. https://www.iana.org/ Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 27 Mommy, where do IP addresses come from? Regional Internet Registries (RIR) manage the allocation and registration of Internet number resources within a region of the world. See also: https://www.xkcd.com/195/ Networking I February 24, 2020
CS615 - Aspects of System Administration Slide 28 Mommy, where do IP addresses come from? RIR s assign blocks of IP addresses to the Local Internet Registries (LIR). LIRs are either ISPs, enterprises using a lot of addresses, or academic institutions. Networking I February 24, 2020
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