Компютърни Мрежи и GNU/Linux

Боян Кроснов

boyan@krosnov.org http://boyan.krosnov.org/

Мариян Маринов

mm@yuhu.bizSiteGround LLC

2

Лекцията

Преговор Linux Networking Stack Команди – IP ARP протокол Команди – ARP Sniffers TCP и UDP протоколи Команди – TCP и UDP

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Преговор

4

Слоести мрежови модели

1. Physical

2. Datalink

3. Network

4. Transport

5. Session

6. Presentation

7. Application

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6

Протоколи

1. baseband, *PSK, QAM-*, OFDM, CDMA, etc. overCat5, Fiber, HFC, phone line, RF etc.

2. Ethernet (802.3) , 802.11, 802.15, 802.16, PPP

3. IP/IPv6

4 and 5. TCP, UDP, RTP

7. HTTP, FTP, SMTP, POP3, IMAP4, SIP, XMPP, IRC, SNMP, SSH, TELNET, DNS, NTP, DHCP

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Мрежова топология

router

subnet, (V)LAN

hosthost

host

host

subnet, (V)LAN

host host

host

subnet, (V)LAN

host

host

host

hostsubnet, (V)LAN

router

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Команди

lspci ip link ethtool, mii-tool ifconfig; /proc/net/dev vconfig; /proc/net/vlan

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Demo setup

Ethernet LAN

luna

Wireless LAN

boyangamelon

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Ethernet LAN

luna

Wireless LAN

boyangamelon

10.126.0.0/24.1 .2 10.126.1.0/24.1 .2

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NIC

NIC

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Linux kernel networking stack

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Linux kernel

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Команди - IP

ipcalc ip addr; ifconfig ip route; route ping; fping traceroute; mtr /etc/network/interfaces (Debian)

/etc/sysconfig/network-scripts (Redhat)

ARP Protocol

RFC826: Ethernet Address Resolution Protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware. D. Plummer. November 1982. (Format: TXT=21556 bytes) (Also STD0037) (Status: STANDARD)

Команди - ARP

ip neigh, arp arping

ARP Table

gw:~# arp -n

Address HWtype HWaddress Flags Mask Iface

192.168.0.5 ether 00:0B:DB:4A:BD:8A C eth1

192.168.0.10 ether 00:0E:A6:6A:B1:12 C eth1

192.168.0.150 ether 00:14:BF:2C:94:5A C eth1

172.16.0.199 ether 00:13:02:4F:78:16 C eth1

192.168.0.124 ether 00:1C:BF:0F:24:F9 C eth1

172.16.0.22 (incomplete) eth1

85.14.21.165 ether 00:17:0F:AD:E1:C0 C eth0

85.14.21.44 ether 00:19:66:34:B1:24 CM eth0

MAC address table

Switch# show mac-address-table vlan 254

. . .

vlan mac address type learn age ports

------+----------------+--------+-----+----------+-----------------

* 254 0004.6a00.326c dynamic Yes 5 Gi1/29

* 254 0003.f402.60e5 dynamic Yes 0 Gi1/3

* 254 0004.6a00.35c0 dynamic Yes 5 Gi1/3

* 254 0004.6a00.31dc dynamic Yes 5 Gi1/3

* 254 0040.c7f6.11e3 dynamic Yes 0 Gi1/3

* 254 0004.6a00.3004 dynamic Yes 5 Gi1/3

* 254 0004.6a00.350c dynamic Yes 5 Gi1/3

* 254 0004.6a00.3720 dynamic Yes 5 Gi1/3

. . .

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Sniffers

Wireshark, tshark

tcpdump

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Демонстрация

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Q&A

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TCP и UDP протоколи

UDP (RFC768 J.Postel 1980)– ports

TCP (RFC793 J.Postel 1981)– Session establishment and tear-down– Window procedure– Slow start and congestion avoidance (VJ 1988)

Berkeley sockets (1983)– The Berkeley socket API forms the de facto

standard abstraction for network sockets. Most other programing languages use an interface similar to the C API. // wikipedia

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Протоколи

1. baseband, *PSK, QAM-*, OFDM, CDMA, etc. overCat5, Fiber, HFC, phone line, RF etc.

2. Ethernet (802.3) , 802.11, 802.15, 802.16, PPP

3. IP/IPv6

4 and 5. TCP, UDP, RTP

7. HTTP, FTP, SMTP, POP3, IMAP4, SIP, XMPP, IRC, SNMP, SSH, TELNET, DNS, NTP, DHCP

UDP header

0 7 8 15 16 23 24 31

+--------+--------+--------+--------+

| Source | Destination |

| Port | Port |

+--------+--------+--------+--------+

| | |

| Length | Checksum |

+--------+--------+--------+--------+

|

| data octets ...

+---------------- ...

User Datagram Header Format

TCP Header

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Source Port | Destination Port |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Sequence Number |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Acknowledgment Number |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Data | |U|A|P|R|S|F| |

| Offset| Reserved |R|C|S|S|Y|I| Window |

| | |G|K|H|T|N|N| |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Checksum | Urgent Pointer |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Options | Padding |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| data |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

TCP Header Format

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Linux kernel networking stack

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TCP и UDP команди

telnet tcptraceroute netstat, fuser, lsof hping nc - TCP/IP swiss army knife

/etc/inetd.conf

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Q&A

Extra slides

iptables

Netfilter firewall

connection tracking

filter, nat, mangle, raw

Linux router

ip route zebra/quagga XORP, Vyatta

Linux bridge (switch)

brctl

ebtables

IP Fragmentation, MTU, PMTU-D

MTU concept TCP MSS DF (Don't Fragment) bit

ICMP type 3 (destination unreachable), code 4 (fragmentation needed but don't-fragment bit set)