Sannu kowa da kowa, sunana Sasha, Ina jagorantar gwajin baya a FunCorp. Mu, kamar sauran mutane da yawa, mun aiwatar da gine-ginen da ya dace da sabis. A gefe guda, wannan yana sauƙaƙe aikin, saboda ... Yana da sauƙi don gwada kowane sabis daban, amma a gefe guda, akwai buƙatar gwada hulɗar ayyuka da juna, wanda sau da yawa yakan faru akan hanyar sadarwa.
A cikin wannan labarin, zan yi magana game da abubuwan amfani guda biyu waɗanda za a iya amfani da su don bincika al'amuran asali waɗanda ke bayyana aikin aikace-aikacen a gaban matsalolin hanyar sadarwa.
Simulating matsalolin cibiyar sadarwa
Yawanci, ana gwada software akan sabar gwaji tare da haɗin Intanet mai kyau. A cikin matsanancin yanayin samarwa, abubuwa bazai zama santsi ba, don haka wani lokacin kuna buƙatar gwada shirye-shirye a cikin yanayin haɗin kai mara kyau. A Linux, mai amfani zai taimaka tare da aikin simintin irin waɗannan yanayi tc.
tc(abbr. daga Kula da zirga-zirga) yana ba ku damar saita jigilar fakitin cibiyar sadarwa a cikin tsarin. Wannan mai amfani yana da babban damar, za ka iya karanta game da su . Anan zan yi la'akari da kaɗan daga cikinsu: muna sha'awar tsarin zirga-zirga, wanda muke amfani da shi qdisc, kuma tunda muna buƙatar yin koyi da hanyar sadarwa mara ƙarfi, za mu yi amfani da qdisc mara aji .
Bari mu ƙaddamar da sabar echo akan uwar garken (Na yi amfani da ):
ncat -l 127.0.0.1 12345 -k -c 'xargs -n1 -i echo "Response: {}"'
Domin nuna dalla-dalla duk tamburan lokaci a kowane mataki na hulɗar tsakanin abokin ciniki da uwar garken, na rubuta rubutun Python mai sauƙi wanda ke aika da bukata. gwajin zuwa uwar garken echo namu.
Lambar tushen abokin ciniki
#!/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
Bari mu kaddamar da shi da kuma dubi zirga-zirga a kan dubawa lo da tashar jiragen ruwa 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
Juji na zirga-zirga
[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
Komai daidai yake: musafiha ta hanyoyi uku, PSH / ACK da ACK a amsa sau biyu - wannan shine musayar buƙatu da amsa tsakanin abokin ciniki da uwar garken, da FIN / ACK da ACK sau biyu - kammala haɗin gwiwa.
Jinkirin fakiti
Yanzu bari mu saita jinkiri zuwa 500 millise seconds:
tc qdisc add dev lo root netem delay 500ms
Mun ƙaddamar da abokin ciniki kuma mu ga cewa rubutun yanzu yana aiki na 2 seconds:
[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
Me ke cikin zirga-zirga? Mu duba:
Juji na zirga-zirga
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
Kuna iya ganin cewa ragi da ake tsammanin na rabin daƙiƙa ya bayyana a cikin hulɗar tsakanin abokin ciniki da uwar garken. Tsarin yana aiki da ban sha'awa sosai idan lag ɗin ya fi girma: kernel ya fara aika wasu fakitin TCP. Bari mu canza jinkiri zuwa daƙiƙa 1 kuma mu duba zirga-zirga (Ba zan nuna fitowar abokin ciniki ba, akwai daƙiƙa 4 da ake tsammani a cikin jimlar tsawon lokaci):
tc qdisc change dev lo root netem delay 1s
Juji na zirga-zirga
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
Ana iya ganin abokin ciniki ya aika fakitin SYN sau biyu, sabar kuma ta aika SYN/ACK sau biyu.
Bugu da ƙari ga ƙima mai ɗorewa, ana iya saita jinkirin zuwa ƙetare, aikin rarrabawa, da haɗin kai (tare da ƙimar fakitin da ya gabata). Ana yin haka kamar haka:
tc qdisc change dev lo root netem delay 500ms 400ms 50 distribution normal
Anan mun saita jinkiri tsakanin milliseconds 100 da 900, za a zaɓi ƙimar bisa ga rarraba ta al'ada kuma za a sami alaƙar 50% tare da ƙimar jinkiri don fakitin da ya gabata.
Wataƙila kun lura cewa a cikin umarnin farko da na yi amfani da shi ƙarasannan canji. Ma'anar waɗannan umarni a bayyane take, don haka zan ƙara cewa akwai ƙari del, wanda za'a iya amfani dashi don cire sanyi.
Asarar fakiti
Bari yanzu muyi ƙoƙarin yin asarar fakiti. Kamar yadda ake iya gani daga takardun, ana iya yin hakan ta hanyoyi uku: asarar fakiti ba da gangan ba tare da wasu yuwuwar, ta amfani da sarkar Markov na jihohi 2, 3 ko 4 don ƙididdige asarar fakiti, ko amfani da samfurin Elliott-Gilbert. A cikin labarin zan yi la'akari da hanya ta farko (mafi sauƙi kuma mafi bayyane), kuma za ku iya karanta game da wasu .
Bari mu yi asarar 50% na fakiti tare da daidaitawa na 25%:
tc qdisc add dev lo root netem loss 50% 25%
Abin takaici, tppdump ba zai iya nuna mana asarar fakiti a fili ba, za mu ɗauka cewa da gaske yana aiki. Kuma ƙarar lokacin gudu da rashin kwanciyar hankali na rubutun zai taimaka mana mu tabbatar da hakan. abokin ciniki.py (ana iya kammalawa nan take, ko watakila a cikin daƙiƙa 20), da kuma ƙarin adadin fakitin da aka sake aikawa:
[user@host ~]# netstat -s | grep retransmited; sleep 10; netstat -s | grep retransmited
17147 segments retransmited
17185 segments retransmited
Ƙara hayaniya zuwa fakiti
Baya ga asarar fakiti, zaku iya kwaikwayi lalacewar fakiti: hayaniya zata bayyana a wurin fakitin bazuwar. Bari mu lalata fakiti tare da yuwuwar 50% kuma ba tare da alaƙa ba:
tc qdisc change dev lo root netem corrupt 50%
Muna gudanar da rubutun abokin ciniki (babu wani abu mai ban sha'awa a can, amma ya ɗauki 2 seconds don kammala), duba zirga-zirga:
Juji na zirga-zirga
[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
Ana iya ganin cewa an aika wasu fakiti akai-akai kuma akwai fakiti guda ɗaya tare da karyewar metadata: zažužžukan [nop, ba a sani ba-65 0x0a3dcf62eb3d,[mara kyau zaɓi]>. Amma babban abu shi ne cewa a ƙarshe duk abin da ya yi aiki daidai - TCP ya jimre da aikinsa.
Kwafin fakiti
Me kuma za ku iya yi da shi netem? Misali, kwaikwayi yanayin juzu'i na asarar fakiti - kwafin fakiti. Wannan umarni kuma yana ɗaukar gardama guda 2: yuwuwa da daidaitawa.
tc qdisc change dev lo root netem duplicate 50% 25%
Canza tsari na fakiti
Kuna iya haɗa jaka ta hanyoyi biyu.
A cikin farko, ana aika wasu fakiti nan da nan, sauran tare da takamaiman jinkiri. Misali daga takardun:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50%
Tare da yuwuwar 25% (da kuma daidaitawar 50%) za a aika fakitin nan da nan, sauran za a aika tare da jinkiri na milliseconds 10.
Hanya ta biyu ita ce lokacin da aka aika kowane fakitin Nth nan take tare da yuwuwar da aka bayar (da alaƙa), sauran kuma tare da jinkirin da aka bayar. Misali daga takardun:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50% gap 5
Kowane fakiti na biyar yana da damar 25% na aika ba tare da bata lokaci ba.
Canza bandwidth
Yawanci ko'ina suke nufi , amma tare da taimakon netem Hakanan zaka iya canza bandwidth na dubawa:
tc qdisc change dev lo root netem rate 56kbit
Wannan tawagar za ta yi zagayawa Localhost mai raɗaɗi kamar hawan Intanet ta hanyar modem ɗin bugun kira. Baya ga saita bitrate, zaku iya kwaikwayi tsarin layin layi na hanyar haɗin gwiwa: saita saman fakiti, girman tantanin halitta, da saman kan tantanin halitta. Misali, ana iya kwaikwayi wannan da bitrate 56 kbit/sec:
tc qdisc change dev lo root netem rate 56kbit 0 48 5
Ƙaddamar da haɗin gwiwa
Wani muhimmin batu a cikin shirin gwaji lokacin karɓar software shine ƙarewar lokaci. Wannan yana da mahimmanci saboda a cikin tsarin da aka rarraba, lokacin da ɗaya daga cikin ayyukan ya ƙare, dole ne sauran su koma ga wasu a cikin lokaci ko mayar da kuskure ga abokin ciniki, kuma a cikin wani hali kada su rataye kawai, jiran amsa ko haɗi. da za a kafa.
Akwai hanyoyi da yawa don yin haka: alal misali, yi amfani da izgili wanda ba ya amsawa, ko haɗi zuwa tsarin ta amfani da debugger, sanya wurin karya a wurin da ya dace kuma dakatar da tsarin (wannan ita ce hanya mafi karkatacciyar hanya). Amma ɗayan mafi bayyane shine zuwa tashar jiragen ruwa ta Firewall ko runduna. Zai taimake mu da wannan .
Don nunawa, za mu yi amfani da tashar wuta ta 12345 kuma za mu gudanar da rubutun abokin ciniki. Kuna iya fakiti masu fita ta wuta zuwa wannan tashar jiragen ruwa a mai aikawa ko fakiti masu shigowa a mai karɓa. A cikin misalan nawa, fakiti masu shigowa za a yi ta wuta (muna amfani da sarkar INPUT da zaɓi --daport). Irin waɗannan fakitin na iya zama DROP, KI ko ƙin yarda tare da Tutar TCP RST, ko tare da rundunar ICMP ba za a iya kaiwa ba (a zahiri, tsohuwar ɗabi'ar ita ce. icmp-tashar jiragen ruwa-ba za a iya isa ba, kuma akwai kuma damar aika amsa icmp-net-ba za a iya isa ba, icmp-proto-wanda ba za a iya kaiwa ba, icmp-net-an haramta и icmp-mai watsa shiri-an haramta).
SHA
Idan akwai ka'ida tare da DROP, fakiti za su "ɓace kawai".
iptables -A INPUT -p tcp --dport 12345 -j DROP
Mun kaddamar da abokin ciniki kuma mu ga cewa yana daskarewa a matakin haɗi zuwa uwar garken. Bari mu kalli zirga-zirga:
Juji na zirga-zirga
[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
Ana iya ganin cewa abokin ciniki yana aika fakitin SYN tare da ƙayyadaddun ƙayyadaddun lokaci. Don haka mun sami ƙaramin kwaro a cikin abokin ciniki: kuna buƙatar amfani da hanyar saita lokaci()don iyakance lokacin da abokin ciniki zai yi ƙoƙarin haɗi zuwa uwar garken.
Nan take muka cire dokar:
iptables -D INPUT -p tcp --dport 12345 -j DROPKuna iya share duk dokoki a lokaci ɗaya:
iptables -F
Idan kuna amfani da Docker kuma kuna buƙatar Tacewar zaɓi duk zirga-zirgar da ke zuwa akwati, to zaku iya yin haka kamar haka:
iptables -I DOCKER-USER -p tcp -d CONTAINER_IP -j DROP
FADA
Yanzu bari mu ƙara irin wannan doka, amma tare da REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT
Abokin ciniki yana fita bayan daƙiƙa tare da kuskure [Kuskure 111] Haɗin ya ƙi. Bari mu kalli zirga-zirgar 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
Ana iya ganin cewa abokin ciniki ya karbi sau biyu tashar jiragen ruwa ba za a iya isa ba sannan ya ƙare da kuskure.
REJECT tare da tcp-sake saitin
Bari mu yi ƙoƙarin ƙara zaɓin --ƙi-tare da tcp-sake saitin:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with tcp-reset
A wannan yanayin, abokin ciniki nan da nan ya fita tare da kuskure, saboda buƙatar farko ta sami fakitin 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
KITA tare da icmp-host-wanda ba a iya isa ga shi
Bari mu gwada wani zaɓi don amfani da REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with icmp-host-unreachable
Abokin ciniki yana fita bayan daƙiƙa tare da kuskure [Kuskure 113] Babu hanyar zuwa masauki, muna gani a cikin zirga-zirgar ICMP Mai watsa shiri na ICMP 127.0.0.1 ba za a iya kaiwa ba.
Hakanan zaka iya gwada sauran sigogin REJECT, kuma zan mayar da hankali kan waɗannan :)
Ƙayyadaddun lokaci na buƙatar simula
Wani yanayi shine lokacin da abokin ciniki ya sami damar haɗi zuwa uwar garken, amma ba zai iya aika buƙatun zuwa gare shi ba. Yadda ake tace fakiti don kar a fara tacewa nan take? Idan ka kalli yadda ake zirga-zirgar duk wata hanyar sadarwa tsakanin abokin ciniki da uwar garken, za ka lura cewa lokacin da ake kafa haɗin yanar gizo, ana amfani da tutocin SYN da ACK kawai, amma lokacin musayar bayanai, fakitin buƙata na ƙarshe zai ƙunshi tutar PSH. Yana shigarwa ta atomatik don guje wa buffer. Kuna iya amfani da wannan bayanin don ƙirƙirar tacewa: zai ba da izinin duk fakiti banda waɗanda ke ɗauke da tutar PSH. Don haka, za a kafa haɗin kai, amma abokin ciniki ba zai iya aika bayanai zuwa uwar garken ba.
SHA
Don DROP umurnin zai yi kama da haka:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j DROP
Kaddamar da abokin ciniki kuma duba zirga-zirga:
Juji na zirga-zirga
[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
Mun ga cewa an kafa haɗin kuma abokin ciniki ba zai iya aika bayanai zuwa uwar garken ba.
FADA
A wannan yanayin hali zai kasance iri ɗaya: abokin ciniki ba zai iya aika buƙatar ba, amma zai karɓa ICMP 127.0.0.1 tcp tashar jiragen ruwa 12345 ba za a iya isa ba kuma ƙara lokaci tsakanin buƙatar sake ƙaddamarwa da yawa. Umurnin yayi kama da haka:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT
REJECT tare da tcp-sake saitin
Umurnin yayi kama da haka:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT --reject-with tcp-reset
Mun riga mun san cewa lokacin amfani --ƙi-tare da tcp-sake saitin abokin ciniki zai karɓi fakitin RST don amsawa, don haka ana iya hasashen halayen: karɓar fakitin RST yayin da aka kafa haɗin yana nufin an rufe soket ɗin ba zato ba tsammani a ɗayan gefen, wanda ke nufin abokin ciniki ya karɓi. Sake saitin haɗin kai ta ɗan ƙera. Bari mu gudanar da rubutun mu kuma mu tabbatar da wannan. Kuma wannan shine yadda zirga-zirgar zai kasance kamar haka:
Juji na zirga-zirga
[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
KITA tare da icmp-host-wanda ba a iya isa ga shi
Ina tsammanin ya riga ya bayyana ga kowa da kowa yadda umarnin zai yi kama da :) Halin abokin ciniki a cikin wannan yanayin zai zama dan kadan daban-daban daga wannan tare da sauƙi REJECT: abokin ciniki ba zai ƙara yawan lokaci ba tsakanin ƙoƙarin sake aikawa da fakitin.
[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
ƙarshe
Ba lallai ba ne a rubuta izgili don gwada hulɗar sabis tare da abokin ciniki ko uwar garken da aka rataye; wani lokacin ya isa a yi amfani da daidaitattun kayan aikin da aka samo a cikin Linux.
Abubuwan amfani da aka tattauna a cikin labarin suna da ƙarin ƙarfi fiye da yadda aka kwatanta, saboda haka zaku iya fitar da wasu zaɓuɓɓukan ku don amfani da su. Da kaina, koyaushe ina da isasshen abin da na rubuta game da shi (a zahiri, har ma da ƙasa). Idan kuna amfani da waɗannan ko makamantan abubuwan amfani a gwaji a cikin kamfanin ku, da fatan za a rubuta yadda daidai. Idan ba haka ba, to ina fata software ɗin ku za ta zama mafi inganci idan kun yanke shawarar gwada ta ta fuskantar matsalolin hanyar sadarwa ta amfani da hanyoyin da aka ba da shawara.
source: www.habr.com