Halo kabeh, jenengku Sasha, aku mimpin tes backend ing FunCorp. Kita, kaya akeh liyane, wis ngetrapake arsitektur berorientasi layanan. Ing tangan siji, iki nyederhanakake karya, amarga ... Luwih gampang kanggo nguji saben layanan kanthi kapisah, nanging ing sisih liya, perlu kanggo nguji interaksi layanan karo saben liyane, sing asring ana ing jaringan.
Ing artikel iki, aku bakal ngomong babagan rong keperluan sing bisa digunakake kanggo mriksa skenario dhasar sing nggambarake operasi aplikasi nalika ana masalah jaringan.
Simulasi masalah jaringan
Biasane, piranti lunak diuji ing server uji kanthi sambungan Internet sing apik. Ing lingkungan produksi atos, iku bisa uga ora dadi Gamelan, supaya kadhangkala sampeyan kudu nyoba program ing kahanan sambungan miskin. Ing Linux, sarana kasebut bakal mbantu tugas simulasi kahanan kasebut tc.
tc(abbr. saka Traffic Control) ngidini sampeyan ngatur transmisi paket jaringan ing sistem. Utilitas iki nduweni kemampuan gedhe, sampeyan bisa maca liyane babagan . Ing kene aku bakal nimbang mung sawetara: kita kasengsem ing jadwal lalu lintas, sing digunakake qdisc, lan amarga kita kudu niru jaringan sing ora stabil, kita bakal nggunakake qdisc tanpa kelas .
Ayo miwiti server echo ing server (aku nggunakake ):
ncat -l 127.0.0.1 12345 -k -c 'xargs -n1 -i echo "Response: {}"'
Kanggo nampilake kanthi rinci kabeh cap wektu ing saben langkah interaksi antarane klien lan server, aku nulis skrip Python prasaja sing ngirim panjalukan. test menyang server gema kita.
Kode sumber klien
#!/bin/python
import socket
import time
HOST = '127.0.0.1'
PORT = 12345
BUFFER_SIZE = 1024
MESSAGE = "Testn"
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
t1 = time.time()
print "[time before connection: %.5f]" % t1
s.connect((HOST, PORT))
print "[time after connection, before sending: %.5f]" % time.time()
s.send(MESSAGE)
print "[time after sending, before receiving: %.5f]" % time.time()
data = s.recv(BUFFER_SIZE)
print "[time after receiving, before closing: %.5f]" % time.time()
s.close()
t2 = time.time()
print "[time after closing: %.5f]" % t2
print "[total duration: %.5f]" % (t2 - t1)
print data
Ayo diluncurake lan deleng lalu lintas ing antarmuka lo lan port 12345:
[user@host ~]# python client.py
[time before connection: 1578652979.44837]
[time after connection, before sending: 1578652979.44889]
[time after sending, before receiving: 1578652979.44894]
[time after receiving, before closing: 1578652979.45922]
[time after closing: 1578652979.45928]
[total duration: 0.01091]
Response: Test
Mbusak lalu lintas
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:42:59.448601 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [S], seq 3383332866, win 43690, options [mss 65495,sackOK,TS val 606325685 ecr 0,nop,wscale 7], length 0
10:42:59.448612 IP 127.0.0.1.12345 > 127.0.0.1.54054: Flags [S.], seq 2584700178, ack 3383332867, win 43690, options [mss 65495,sackOK,TS val 606325685 ecr 606325685,nop,wscale 7], length 0
10:42:59.448622 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 606325685 ecr 606325685], length 0
10:42:59.448923 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 606325685 ecr 606325685], length 5
10:42:59.448930 IP 127.0.0.1.12345 > 127.0.0.1.54054: Flags [.], ack 6, win 342, options [nop,nop,TS val 606325685 ecr 606325685], length 0
10:42:59.459118 IP 127.0.0.1.12345 > 127.0.0.1.54054: Flags [P.], seq 1:15, ack 6, win 342, options [nop,nop,TS val 606325696 ecr 606325685], length 14
10:42:59.459213 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [.], ack 15, win 342, options [nop,nop,TS val 606325696 ecr 606325696], length 0
10:42:59.459268 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [F.], seq 6, ack 15, win 342, options [nop,nop,TS val 606325696 ecr 606325696], length 0
10:42:59.460184 IP 127.0.0.1.12345 > 127.0.0.1.54054: Flags [F.], seq 15, ack 7, win 342, options [nop,nop,TS val 606325697 ecr 606325696], length 0
10:42:59.460196 IP 127.0.0.1.54054 > 127.0.0.1.12345: Flags [.], ack 16, win 342, options [nop,nop,TS val 606325697 ecr 606325697], length 0
Kabeh iku standar: jabat tangan telung cara, PSH / ACK lan ACK nanggepi kaping pindho - iki ijol-ijolan panyuwunan lan respon antarane klien lan server, lan FIN / ACK lan ACK kaping pindho - ngrampungake sambungan.
Paket tunda
Saiki ayo nyetel wektu tundha dadi 500 milidetik:
tc qdisc add dev lo root netem delay 500ms
Kita miwiti klien lan ndeleng manawa skrip saiki mlaku sajrone 2 detik:
[user@host ~]# ./client.py
[time before connection: 1578662612.71044]
[time after connection, before sending: 1578662613.71059]
[time after sending, before receiving: 1578662613.71065]
[time after receiving, before closing: 1578662614.72011]
[time after closing: 1578662614.72019]
[total duration: 2.00974]
Response: Test
Apa ing lalu lintas? Ayo katon:
Mbusak lalu lintas
13:23:33.210520 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [S], seq 1720950927, win 43690, options [mss 65495,sackOK,TS val 615958947 ecr 0,nop,wscale 7], length 0
13:23:33.710554 IP 127.0.0.1.12345 > 127.0.0.1.58694: Flags [S.], seq 1801168125, ack 1720950928, win 43690, options [mss 65495,sackOK,TS val 615959447 ecr 615958947,nop,wscale 7], length 0
13:23:34.210590 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 615959947 ecr 615959447], length 0
13:23:34.210657 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 615959947 ecr 615959447], length 5
13:23:34.710680 IP 127.0.0.1.12345 > 127.0.0.1.58694: Flags [.], ack 6, win 342, options [nop,nop,TS val 615960447 ecr 615959947], length 0
13:23:34.719371 IP 127.0.0.1.12345 > 127.0.0.1.58694: Flags [P.], seq 1:15, ack 6, win 342, options [nop,nop,TS val 615960456 ecr 615959947], length 14
13:23:35.220106 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [.], ack 15, win 342, options [nop,nop,TS val 615960957 ecr 615960456], length 0
13:23:35.220188 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [F.], seq 6, ack 15, win 342, options [nop,nop,TS val 615960957 ecr 615960456], length 0
13:23:35.720994 IP 127.0.0.1.12345 > 127.0.0.1.58694: Flags [F.], seq 15, ack 7, win 342, options [nop,nop,TS val 615961457 ecr 615960957], length 0
13:23:36.221025 IP 127.0.0.1.58694 > 127.0.0.1.12345: Flags [.], ack 16, win 342, options [nop,nop,TS val 615961957 ecr 615961457], length 0
Sampeyan bisa ndeleng manawa lag samesthine setengah detik wis katon ing interaksi antarane klien lan server. Sistem tumindak luwih menarik yen lag luwih gedhe: kernel wiwit ngirim maneh sawetara paket TCP. Ayo ngganti wektu tundha dadi 1 detik lan deleng lalu lintas (Aku ora bakal nuduhake output klien, ana sing dikarepake 4 detik ing total durasi):
tc qdisc change dev lo root netem delay 1s
Mbusak lalu lintas
13:29:07.709981 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [S], seq 283338334, win 43690, options [mss 65495,sackOK,TS val 616292946 ecr 0,nop,wscale 7], length 0
13:29:08.710018 IP 127.0.0.1.12345 > 127.0.0.1.39306: Flags [S.], seq 3514208179, ack 283338335, win 43690, options [mss 65495,sackOK,TS val 616293946 ecr 616292946,nop,wscale 7], length 0
13:29:08.711094 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [S], seq 283338334, win 43690, options [mss 65495,sackOK,TS val 616293948 ecr 0,nop,wscale 7], length 0
13:29:09.710048 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 616294946 ecr 616293946], length 0
13:29:09.710152 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 616294947 ecr 616293946], length 5
13:29:09.711120 IP 127.0.0.1.12345 > 127.0.0.1.39306: Flags [S.], seq 3514208179, ack 283338335, win 43690, options [mss 65495,sackOK,TS val 616294948 ecr 616292946,nop,wscale 7], length 0
13:29:10.710173 IP 127.0.0.1.12345 > 127.0.0.1.39306: Flags [.], ack 6, win 342, options [nop,nop,TS val 616295947 ecr 616294947], length 0
13:29:10.711140 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 616295948 ecr 616293946], length 0
13:29:10.714782 IP 127.0.0.1.12345 > 127.0.0.1.39306: Flags [P.], seq 1:15, ack 6, win 342, options [nop,nop,TS val 616295951 ecr 616294947], length 14
13:29:11.714819 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [.], ack 15, win 342, options [nop,nop,TS val 616296951 ecr 616295951], length 0
13:29:11.714893 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [F.], seq 6, ack 15, win 342, options [nop,nop,TS val 616296951 ecr 616295951], length 0
13:29:12.715562 IP 127.0.0.1.12345 > 127.0.0.1.39306: Flags [F.], seq 15, ack 7, win 342, options [nop,nop,TS val 616297952 ecr 616296951], length 0
13:29:13.715596 IP 127.0.0.1.39306 > 127.0.0.1.12345: Flags [.], ack 16, win 342, options [nop,nop,TS val 616298952 ecr 616297952], length 0
Bisa dideleng manawa klien ngirim paket SYN kaping pindho, lan server ngirim SYN / ACK kaping pindho.
Saliyane nilai konstan, wektu tundha bisa disetel menyang penyimpangan, fungsi distribusi, lan korélasi (kanthi nilai kanggo paket sadurunge). Iki ditindakake kaya ing ngisor iki:
tc qdisc change dev lo root netem delay 500ms 400ms 50 distribution normal
Ing kene kita wis nyetel wektu tundha antarane 100 lan 900 milidetik, nilai kasebut bakal dipilih miturut distribusi normal lan bakal ana korelasi 50% karo nilai tundha kanggo paket sadurunge.
Sampeyan bisa uga wis ngeweruhi sing ing printah pisanan aku digunakake nambah, lan banjur owah-owahan. Makna perintah kasebut jelas, mula aku bakal nambah manawa ana liyane Del, sing bisa digunakake kanggo mbusak konfigurasi.
Paket Loss
Ayo saiki nyoba nggawe packet loss. Minangka bisa katon saka dokumentasi, iki bisa rampung ing telung cara: rusak paket acak karo sawetara kemungkinan, nggunakake chain Markov 2, 3 utawa 4 negara kanggo ngitung mundhut paket, utawa nggunakake model Elliott-Gilbert. Ing artikel aku bakal nimbang cara pisanan (paling prasaja lan paling ketok), lan sampeyan bisa maca bab liyane .
Ayo nggawe mundhut 50% paket kanthi korelasi 25%:
tc qdisc add dev lo root netem loss 50% 25%
Sayange, tcpdump ora bakal bisa kanggo cetha nuduhake kita mundhut saka paket, kita mung bakal nganggep sing tenan dianggo. Lan wektu skrip sing saya tambah lan ora stabil bakal mbantu kita verifikasi iki. klien.py (bisa rampung kanthi cepet, utawa bisa uga ing 20 detik), uga tambah akeh paket sing dikirim maneh:
[user@host ~]# netstat -s | grep retransmited; sleep 10; netstat -s | grep retransmited
17147 segments retransmited
17185 segments retransmited
Nambahake gangguan menyang paket
Saliyane mundhut paket, sampeyan bisa simulasi karusakan paket: gangguan bakal katon ing posisi paket acak. Ayo gawe karusakan paket kanthi kemungkinan 50% lan tanpa korélasi:
tc qdisc change dev lo root netem corrupt 50%
Kita mbukak skrip klien (ora ana sing menarik, nanging butuh 2 detik kanggo ngrampungake), deleng lalu lintas:
Mbusak lalu lintas
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:20:54.812434 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [S], seq 2023663770, win 43690, options [mss 65495,sackOK,TS val 1037001049 ecr 0,nop,wscale 7], length 0
10:20:54.812449 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [S.], seq 2104268044, ack 2023663771, win 43690, options [mss 65495,sackOK,TS val 1037001049 ecr 1037001049,nop,wscale 7], length 0
10:20:54.812458 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 1037001049 ecr 1037001049], length 0
10:20:54.812509 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1037001049 ecr 1037001049], length 5
10:20:55.013093 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1037001250 ecr 1037001049], length 5
10:20:55.013122 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [.], ack 6, win 342, options [nop,nop,TS val 1037001250 ecr 1037001250], length 0
10:20:55.014681 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [P.], seq 1:15, ack 6, win 342, options [nop,nop,TS val 1037001251 ecr 1037001250], length 14
10:20:55.014745 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [.], ack 15, win 340, options [nop,nop,TS val 1037001251 ecr 1037001251], length 0
10:20:55.014823 IP 127.0.0.1.43666 > 127.0.0.5.12345: Flags [F.], seq 2023663776, ack 2104268059, win 342, options [nop,nop,TS val 1037001251 ecr 1037001251], length 0
10:20:55.214088 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [P.], seq 1:15, ack 6, win 342, options [nop,unknown-65 0x0a3dcf62eb3d,[bad opt]>
10:20:55.416087 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [F.], seq 6, ack 15, win 342, options [nop,nop,TS val 1037001653 ecr 1037001251], length 0
10:20:55.416804 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [F.], seq 15, ack 7, win 342, options [nop,nop,TS val 1037001653 ecr 1037001653], length 0
10:20:55.416818 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [.], ack 16, win 343, options [nop,nop,TS val 1037001653 ecr 1037001653], length 0
10:20:56.147086 IP 127.0.0.1.12345 > 127.0.0.1.43666: Flags [F.], seq 15, ack 7, win 342, options [nop,nop,TS val 1037002384 ecr 1037001653], length 0
10:20:56.147101 IP 127.0.0.1.43666 > 127.0.0.1.12345: Flags [.], ack 16, win 342, options [nop,nop,TS val 1037002384 ecr 1037001653], length 0
Bisa dideleng manawa sawetara paket dikirim bola-bali lan ana siji paket sing metadata rusak: opsi [nop,unknown-65 0x0a3dcf62eb3d,[bad opt]>. Nanging sing utama yaiku ing pungkasan kabeh bisa ditindakake kanthi bener - TCP ngrampungake tugase.
Duplikasi paket
Apa maneh sing bisa ditindakake netem? Contone, simulasi kahanan mbalikke saka mundhut paket-duplikasi paket. Printah iki uga njupuk 2 argumen: probabilitas lan korélasi.
tc qdisc change dev lo root netem duplicate 50% 25%
Ngganti urutan paket
Sampeyan bisa nyampur tas kanthi rong cara.
Kaping pisanan, sawetara paket dikirim langsung, liyane kanthi wektu tundha sing ditemtokake. Tuladha saka dokumentasi:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50%
Kanthi kemungkinan 25% (lan korélasi 50%), paket bakal dikirim langsung, liyane bakal dikirim kanthi wektu tundha 10 milidetik.
Cara kapindho yaiku nalika saben paket Nth dikirim kanthi cepet kanthi kemungkinan (lan korélasi), lan liyane kanthi wektu tundha. Tuladha saka dokumentasi:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50% gap 5
Saben paket kaping lima duwe 25% kasempatan dikirim tanpa wektu tundha.
Ngganti Bandwidth
Biasane nang endi wae sing dirujuk , nanging kanthi bantuan netem Sampeyan uga bisa ngganti bandwidth antarmuka:
tc qdisc change dev lo root netem rate 56kbit
Tim iki bakal nggawe treks watara localhost nglarani kaya surfing internet liwat modem dial-up. Saliyane nyetel bitrate, sampeyan uga bisa niru model protokol lapisan link: nyetel overhead kanggo paket, ukuran sel, lan overhead kanggo sel. Contone, iki bisa simulasi lan bitrate 56 kbit/detik:
tc qdisc change dev lo root netem rate 56kbit 0 48 5
Simulating sambungan wektu entek
Titik penting liyane ing rencana tes nalika nampa piranti lunak yaiku wektu entek. Iki penting amarga ing sistem mbagekke, nalika salah siji layanan dipatèni, liyane kudu bali menyang liyane ing wektu utawa bali kesalahan kanggo klien, lan ing kasus ora kudu padha mung nyumerepi, nunggu respon utawa sambungan. kanggo ditetepake.
Ana sawetara cara kanggo nindakake iki: contone, nggunakake mock sing ora nanggapi, utawa nyambung menyang proses nggunakake debugger a, sijine breakpoint ing Panggonan tengen lan mungkasi proses (iki mbokmenawa cara paling perverted). Nanging salah siji sing paling ketok yaiku port firewall utawa host. Iku bakal bantuan kita karo iki .
Kanggo demonstrasi, kita bakal firewall port 12345 lan mbukak script klien kita. Sampeyan bisa firewall paket metu menyang port iki ing pangirim utawa paket mlebu ing panrima. Ing contoku, paket sing mlebu bakal dibakar (kita nggunakake chain INPUT lan opsi --dport). Paket kasebut bisa DROP, REJECT utawa REJECT kanthi flag TCP RST, utawa karo host ICMP sing ora bisa digayuh (nyatane, prilaku standar yaiku icmp-port-ora bisa digayuh, lan ana uga kesempatan kanggo ngirim balesan icmp-net-ora bisa digayuh, icmp-proto-ora bisa digayuh, icmp-net-dilarang и icmp-host-dilarang).
TUTUP
Yen ana aturan karo DROP, paket mung bakal "ilang".
iptables -A INPUT -p tcp --dport 12345 -j DROP
Kita miwiti klien lan ndeleng manawa beku ing tahap nyambungake menyang server. Ayo ndeleng lalu lintas:
Mbusak lalu lintas
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
08:28:20.213506 IP 127.0.0.1.32856 > 127.0.0.1.12345: Flags [S], seq 3019694933, win 43690, options [mss 65495,sackOK,TS val 1203046450 ecr 0,nop,wscale 7], length 0
08:28:21.215086 IP 127.0.0.1.32856 > 127.0.0.1.12345: Flags [S], seq 3019694933, win 43690, options [mss 65495,sackOK,TS val 1203047452 ecr 0,nop,wscale 7], length 0
08:28:23.219092 IP 127.0.0.1.32856 > 127.0.0.1.12345: Flags [S], seq 3019694933, win 43690, options [mss 65495,sackOK,TS val 1203049456 ecr 0,nop,wscale 7], length 0
08:28:27.227087 IP 127.0.0.1.32856 > 127.0.0.1.12345: Flags [S], seq 3019694933, win 43690, options [mss 65495,sackOK,TS val 1203053464 ecr 0,nop,wscale 7], length 0
08:28:35.235102 IP 127.0.0.1.32856 > 127.0.0.1.12345: Flags [S], seq 3019694933, win 43690, options [mss 65495,sackOK,TS val 1203061472 ecr 0,nop,wscale 7], length 0
Bisa dideleng manawa klien ngirim paket SYN kanthi wektu entek kanthi eksponensial. Dadi, kita nemokake bug cilik ing klien: sampeyan kudu nggunakake metode kasebut settimeout()kanggo matesi wektu sajrone klien bakal nyoba nyambung menyang server.
Kita langsung mbusak aturan kasebut:
iptables -D INPUT -p tcp --dport 12345 -j DROPSampeyan bisa mbusak kabeh aturan bebarengan:
iptables -F
Yen sampeyan nggunakake Docker lan sampeyan kudu firewall kabeh lalu lintas menyang wadhah, sampeyan bisa nindakake kaya ing ngisor iki:
iptables -I DOCKER-USER -p tcp -d CONTAINER_IP -j DROP
GAMPANG
Saiki ayo nambah aturan sing padha, nanging nganggo REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT
Klien metu sawise detik kanthi kesalahan [Errno 111] Sambungan ditolak. Ayo ndeleng lalu lintas ICMP:
[user@host ~]# tcpdump -i lo -nn icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
08:45:32.871414 IP 127.0.0.1 > 127.0.0.1: ICMP 127.0.0.1 tcp port 12345 unreachable, length 68
08:45:33.873097 IP 127.0.0.1 > 127.0.0.1: ICMP 127.0.0.1 tcp port 12345 unreachable, length 68
Bisa dideleng yen klien nampa kaping pindho port ora bisa digayuh banjur dipungkasi karo kesalahan.
REJECT karo tcp-reset
Ayo dadi nyoba kanggo nambah pilihan --reject-with tcp-reset:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with tcp-reset
Ing kasus iki, klien langsung metu kanthi kesalahan, amarga panjalukan pisanan nampa paket RST:
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
09:02:52.766175 IP 127.0.0.1.60658 > 127.0.0.1.12345: Flags [S], seq 1889460883, win 43690, options [mss 65495,sackOK,TS val 1205119003 ecr 0,nop,wscale 7], length 0
09:02:52.766184 IP 127.0.0.1.12345 > 127.0.0.1.60658: Flags [R.], seq 0, ack 1889460884, win 0, length 0
REJECT karo icmp-host-unreachable
Coba opsi liyane kanggo nggunakake REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with icmp-host-unreachable
Klien metu sawise detik kanthi kesalahan [Errno 113] Ora ana rute menyang tuan rumah, kita waca ing lalu lintas ICMP ICMP inang 127.0.0.1 ora bisa digayuh.
Sampeyan uga bisa nyoba parameter REJECT liyane, lan aku bakal fokus ing iki :)
Simulating request wektu entek
Kahanan liyane yaiku nalika klien bisa nyambung menyang server, nanging ora bisa ngirim panjaluk kasebut. Kepiye carane nyaring paket supaya nyaring ora langsung diwiwiti? Yen sampeyan ndeleng lalu lintas komunikasi apa wae antarane klien lan server, sampeyan bakal sok dong mirsani yen nalika nggawe sambungan, mung bendera SYN lan ACK digunakake, nanging nalika ijol-ijolan data, paket panyuwunan pungkasan bakal ngemot flag PSH. Diinstal kanthi otomatis supaya ora buffering. Sampeyan bisa nggunakake informasi iki kanggo nggawe saringan: bakal ngidini kabeh paket kajaba sing ngemot flag PSH. Mangkono, sambungan bakal ditetepake, nanging klien ora bakal bisa ngirim data menyang server.
TUTUP
Kanggo DROP printah bakal katon kaya iki:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j DROP
Bukak klien lan nonton lalu lintas:
Mbusak lalu lintas
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:02:47.549498 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [S], seq 2166014137, win 43690, options [mss 65495,sackOK,TS val 1208713786 ecr 0,nop,wscale 7], length 0
10:02:47.549510 IP 127.0.0.1.12345 > 127.0.0.1.49594: Flags [S.], seq 2341799088, ack 2166014138, win 43690, options [mss 65495,sackOK,TS val 1208713786 ecr 1208713786,nop,wscale 7], length 0
10:02:47.549520 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 1208713786 ecr 1208713786], length 0
10:02:47.549568 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1208713786 ecr 1208713786], length 5
10:02:47.750084 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1208713987 ecr 1208713786], length 5
10:02:47.951088 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1208714188 ecr 1208713786], length 5
10:02:48.354089 IP 127.0.0.1.49594 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1208714591 ecr 1208713786], length 5
Kita weruh manawa sambungan kasebut ditetepake lan klien ora bisa ngirim data menyang server.
GAMPANG
Ing kasus iki prilaku bakal padha: klien ora bakal bisa ngirim panjalukan, nanging bakal nampa ICMP 127.0.0.1 port tcp 12345 ora bisa digayuh lan nambah wektu antarane panjalukan resubmissions exponentially. Printah katon kaya iki:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT
REJECT karo tcp-reset
Printah katon kaya iki:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT --reject-with tcp-reset
Kita wis ngerti yen nalika nggunakake --reject-with tcp-reset klien bakal nampa paket RST kanggo nanggepi, supaya prilaku bisa diprediksi: nampa paket RST nalika sambungan ditetepake tegese soket ndadak ditutup ing sisih liyane, kang tegese klien kudu nampa. Sambungan reset dening peer. Ayo mbukak skrip lan priksa manawa iki. Lan iki bakal katon kaya lalu lintas:
Mbusak lalu lintas
[user@host ~]# tcpdump -i lo -nn port 12345
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:22:14.186269 IP 127.0.0.1.52536 > 127.0.0.1.12345: Flags [S], seq 2615137531, win 43690, options [mss 65495,sackOK,TS val 1209880423 ecr 0,nop,wscale 7], length 0
10:22:14.186284 IP 127.0.0.1.12345 > 127.0.0.1.52536: Flags [S.], seq 3999904809, ack 2615137532, win 43690, options [mss 65495,sackOK,TS val 1209880423 ecr 1209880423,nop,wscale 7], length 0
10:22:14.186293 IP 127.0.0.1.52536 > 127.0.0.1.12345: Flags [.], ack 1, win 342, options [nop,nop,TS val 1209880423 ecr 1209880423], length 0
10:22:14.186338 IP 127.0.0.1.52536 > 127.0.0.1.12345: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 1209880423 ecr 1209880423], length 5
10:22:14.186344 IP 127.0.0.1.12345 > 127.0.0.1.52536: Flags [R], seq 3999904810, win 0, length 0
REJECT karo icmp-host-unreachable
Aku iku wis ketok kanggo everyone apa printah bakal katon kaya :) Prilaku klien ing kasus iki bakal rada beda karo REJECT prasaja: klien ora bakal nambah wektu entek antarane nyoba kanggo ngirim maneh paket.
[user@host ~]# tcpdump -i lo -nn icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:29:56.149202 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:56.349107 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:56.549117 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:56.750125 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:56.951130 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:57.152107 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
10:29:57.353115 IP 127.0.0.1 > 127.0.0.1: ICMP host 127.0.0.1 unreachable, length 65
kesimpulan
Ora perlu nulis mock kanggo nyoba interaksi layanan karo klien utawa server sing digantung; kadhangkala cukup nggunakake utilitas standar sing ditemokake ing Linux.
Utilitas sing dibahas ing artikel kasebut duwe kemampuan luwih akeh tinimbang sing diterangake, supaya sampeyan bisa nemokake sawetara pilihan sampeyan dhewe kanggo nggunakake. Secara pribadi, aku mesthi duwe cukup apa sing dakcritakake (nyatane, malah kurang). Yen sampeyan nggunakake utilitas iki utawa padha ing testing ing perusahaan, please nulis carane persis. Yen ora, muga-muga piranti lunak sampeyan bakal luwih apik yen sampeyan mutusake kanggo nyoba ing kahanan masalah jaringan nggunakake metode sing disaranake.
Source: www.habr.com