Halo watu wote, jina langu ni Sasha, ninaongoza majaribio ya nyuma katika FunCorp. Sisi, kama wengine wengi, tumetekeleza usanifu unaolenga huduma. Kwa upande mmoja, hii hurahisisha kazi, kwa sababu ... Ni rahisi kupima kila huduma tofauti, lakini kwa upande mwingine, kuna haja ya kupima mwingiliano wa huduma kwa kila mmoja, ambayo mara nyingi hutokea kwenye mtandao.
Katika makala hii, nitazungumzia kuhusu huduma mbili ambazo zinaweza kutumika kuangalia matukio ya msingi ambayo yanaelezea uendeshaji wa maombi mbele ya matatizo ya mtandao.
Kuiga matatizo ya mtandao
Kwa kawaida, programu hujaribiwa kwenye seva za majaribio na muunganisho mzuri wa Mtandao. Katika mazingira magumu ya uzalishaji, mambo hayawezi kuwa laini, kwa hivyo wakati mwingine unahitaji kujaribu programu katika hali mbaya ya unganisho. Kwenye Linux, matumizi yatasaidia na kazi ya kuiga hali kama hizo tc.
tc(abbr. kutoka kwa Udhibiti wa Trafiki) inakuwezesha kusanidi maambukizi ya pakiti za mtandao kwenye mfumo. Huduma hii ina uwezo mkubwa, unaweza kusoma zaidi juu yao . Hapa nitazingatia chache tu kati yao: tunavutiwa na ratiba ya trafiki, ambayo tunatumia qdisc, na kwa kuwa tunahitaji kuiga mtandao usio imara, tutatumia qdisc isiyo na darasa .
Wacha tuzindue seva ya mwangwi kwenye seva (nilitumia ):
ncat -l 127.0.0.1 12345 -k -c 'xargs -n1 -i echo "Response: {}"'
Ili kuonyesha kwa undani alama zote za nyakati katika kila hatua ya mwingiliano kati ya mteja na seva, niliandika hati rahisi ya Python ambayo hutuma ombi. Mtihani kwa seva yetu ya echo.
Msimbo wa chanzo cha mteja
#!/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
Wacha tuzindue na tuangalie trafiki kwenye kiolesura lo na bandari 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
Dampo la trafiki
[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
Kila kitu ni cha kawaida: kupeana mkono kwa njia tatu, PSH/ACK na ACK katika jibu mara mbili - hii ni ubadilishanaji wa ombi na majibu kati ya mteja na seva, na FIN/ACK na ACK mara mbili - kukamilisha muunganisho.
Ucheleweshaji wa pakiti
Sasa wacha tuweke kucheleweshwa kwa milisekunde 500:
tc qdisc add dev lo root netem delay 500ms
Tunazindua mteja na kuona kwamba hati sasa inaendesha kwa sekunde 2:
[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
Kuna nini kwenye trafiki? Hebu tuangalie:
Dampo la trafiki
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
Unaweza kuona kwamba lagi inayotarajiwa ya nusu ya pili imeonekana katika mwingiliano kati ya mteja na seva. Mfumo hufanya kazi kwa kupendeza zaidi ikiwa lagi ni kubwa zaidi: kernel huanza kutuma tena pakiti za TCP. Wacha tubadilishe kucheleweshwa hadi sekunde 1 na tuangalie trafiki (Sitaonyesha matokeo ya mteja, kuna sekunde 4 zinazotarajiwa kwa muda wote):
tc qdisc change dev lo root netem delay 1s
Dampo la trafiki
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
Inaweza kuonekana kuwa mteja alituma pakiti ya SYN mara mbili, na seva ilituma SYN/ACK mara mbili.
Kwa kuongeza thamani ya mara kwa mara, ucheleweshaji unaweza kuwekwa kwa kupotoka, chaguo za kukokotoa za usambazaji na uunganisho (na thamani ya pakiti iliyotangulia). Hii inafanywa kama ifuatavyo:
tc qdisc change dev lo root netem delay 500ms 400ms 50 distribution normal
Hapa tumeweka ucheleweshaji kati ya milliseconds 100 na 900, maadili yatachaguliwa kulingana na usambazaji wa kawaida na kutakuwa na uwiano wa 50% na thamani ya kuchelewa kwa pakiti ya awali.
Labda umegundua kuwa katika amri ya kwanza niliyotumia kuongezana kisha mabadiliko ya. Maana ya amri hizi ni dhahiri, kwa hivyo nitaongeza tu kuwa kuna zaidi del, ambayo inaweza kutumika kuondoa usanidi.
Kupoteza Pakiti
Hebu sasa tujaribu kupoteza pakiti. Kama inavyoonekana kutoka kwa hati, hii inaweza kufanywa kwa njia tatu: kupoteza pakiti nasibu na uwezekano fulani, kwa kutumia mlolongo wa Markov wa majimbo 2, 3 au 4 kuhesabu upotezaji wa pakiti, au kwa kutumia mfano wa Elliott-Gilbert. Katika makala nitazingatia njia ya kwanza (rahisi na dhahiri zaidi), na unaweza kusoma kuhusu wengine .
Wacha tupoteze 50% ya pakiti na uunganisho wa 25%:
tc qdisc add dev lo root netem loss 50% 25%
Kwa bahati mbaya, tcpdump haitaweza kutuonyesha wazi upotezaji wa pakiti, tutafikiria tu kuwa inafanya kazi kweli. Na muda wa uendeshaji ulioongezeka na usio thabiti wa hati utatusaidia kuthibitisha hili. mteja.py (inaweza kukamilika mara moja, au labda katika sekunde 20), pamoja na kuongezeka kwa idadi ya pakiti zilizotumwa tena:
[user@host ~]# netstat -s | grep retransmited; sleep 10; netstat -s | grep retransmited
17147 segments retransmited
17185 segments retransmited
Kuongeza kelele kwa pakiti
Mbali na kupoteza pakiti, unaweza kuiga uharibifu wa pakiti: kelele itaonekana kwenye nafasi ya pakiti ya random. Wacha tufanye uharibifu wa pakiti na uwezekano wa 50% na bila uunganisho:
tc qdisc change dev lo root netem corrupt 50%
Tunaendesha hati ya mteja (hakuna kitu cha kufurahisha hapo, lakini ilichukua sekunde 2 kukamilika), angalia trafiki:
Dampo la trafiki
[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
Inaweza kuonekana kuwa pakiti zingine zilitumwa mara kwa mara na kuna pakiti moja iliyo na metadata iliyovunjika: chaguzi [nop,unknown-65 0x0a3dcf62eb3d,[bad opt]>. Lakini jambo kuu ni kwamba mwisho kila kitu kilifanya kazi kwa usahihi - TCP ilikabiliana na kazi yake.
Kurudia kwa pakiti
Nini kingine unaweza kufanya na netem? Kwa mfano, iga hali ya kinyume ya upotevu wa pakitiβrudufu ya pakiti. Amri hii pia inachukua hoja 2: uwezekano na uunganisho.
tc qdisc change dev lo root netem duplicate 50% 25%
Kubadilisha mpangilio wa vifurushi
Unaweza kuchanganya mifuko kwa njia mbili.
Katika kwanza, baadhi ya pakiti hutumwa mara moja, wengine na kuchelewa maalum. Mfano kutoka kwa nyaraka:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50%
Kwa uwezekano wa 25% (na uwiano wa 50%) pakiti itatumwa mara moja, wengine watatumwa kwa kuchelewa kwa milliseconds 10.
Njia ya pili ni wakati kila pakiti ya Nth inatumwa papo hapo na uwezekano fulani (na uunganisho), na iliyobaki kwa kucheleweshwa fulani. Mfano kutoka kwa nyaraka:
tc qdisc change dev lo root netem delay 10ms reorder 25% 50% gap 5
Kila kifurushi cha tano kina nafasi ya 25% ya kutumwa bila kuchelewa.
Kubadilisha Bandwidth
Kawaida kila mahali wanarejelea , lakini kwa msaada netem Unaweza pia kubadilisha kipimo data cha kiolesura:
tc qdisc change dev lo root netem rate 56kbit
Timu hii itafanya safari za kuzunguka lochost chungu kama vile kuvinjari Mtandao kupitia modemu ya kupiga simu. Mbali na kuweka bitrate, unaweza pia kuiga mfano wa itifaki ya safu ya kiungo: weka kichwa cha juu cha pakiti, saizi ya seli, na sehemu ya juu ya seli. Kwa mfano, hii inaweza kuigwa na bitrate 56 kbit/sec:
tc qdisc change dev lo root netem rate 56kbit 0 48 5
Muda wa kuiga muunganisho umekwisha
Jambo lingine muhimu katika mpango wa jaribio wakati wa kukubali programu ni kuisha. Hii ni muhimu kwa sababu katika mifumo iliyosambazwa, wakati moja ya huduma imezimwa, wengine wanapaswa kurudi kwa wengine kwa wakati au kurudisha kosa kwa mteja, na kwa hali yoyote hawapaswi kunyongwa tu, wakingojea jibu au unganisho. kuanzishwa.
Kuna njia kadhaa za kufanya hivi: kwa mfano, tumia dhihaka ambayo haijibu, au unganisha kwa mchakato kwa kutumia debugger, weka sehemu ya kuvunja mahali pazuri na usimamishe mchakato (hii labda ndiyo njia iliyopotoka zaidi). Lakini moja ya dhahiri zaidi ni bandari za firewall au majeshi. Itatusaidia kwa hili .
Kwa onyesho, tutaweka ngome ya ngome 12345 na kuendesha hati ya mteja wetu. Unaweza ngome ya pakiti zinazotoka kwenye mlango huu kwa mtumaji au pakiti zinazoingia kwenye kipokezi. Katika mifano yangu, pakiti zinazoingia zitawekwa moto (tunatumia INPUT ya mnyororo na chaguo --dport) Pakiti kama hizo zinaweza DROP, REJECT au REJECT na bendera ya TCP RST, au kwa seva pangishi ya ICMP isiyoweza kufikiwa (kwa kweli, tabia chaguo-msingi ni icmp-bandari-isiyoweza kufikiwa, na pia kuna fursa ya kutuma jibu icmp-net-isiyoweza kufikiwa, icmp-proto-isiyoweza kufikiwa, icmp-net-marufuku ΠΈ icmp-mwenyeji-imepigwa marufuku).
DHAMBI
Ikiwa kuna sheria na DROP, pakiti "zitatoweka".
iptables -A INPUT -p tcp --dport 12345 -j DROP
Tunazindua mteja na kuona kwamba inafungia katika hatua ya kuunganisha kwenye seva. Wacha tuangalie trafiki:
Dampo la trafiki
[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
Inaweza kuonekana kuwa mteja hutuma pakiti za SYN na muda wa kuisha unaoongezeka kwa kasi. Kwa hiyo tulipata mdudu mdogo katika mteja: unahitaji kutumia njia kuweka muda()ili kupunguza muda ambao mteja atajaribu kuunganisha kwenye seva.
Tunaondoa sheria mara moja:
iptables -D INPUT -p tcp --dport 12345 -j DROPUnaweza kufuta sheria zote mara moja:
iptables -F
Ikiwa unatumia Docker na unahitaji kuwasha trafiki yote kwenda kwenye chombo, basi unaweza kuifanya kama ifuatavyo.
iptables -I DOCKER-USER -p tcp -d CONTAINER_IP -j DROP
KATAA
Sasa wacha tuongeze sheria kama hiyo, lakini kwa REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT
Mteja hutoka baada ya sekunde na hitilafu [Errno 111] Muunganisho ulikataliwa. Wacha tuangalie trafiki ya 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
Inaweza kuonekana kuwa mteja alipokea mara mbili bandari haipatikani na kisha kuishia na kosa.
KATAA kwa kuweka upya tcp
Hebu jaribu kuongeza chaguo --kataa-na tcp-reset:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with tcp-reset
Katika kesi hii, mteja hutoka mara moja na kosa, kwa sababu ombi la kwanza lilipokea pakiti ya 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
KATAA na icmp-host-isiyoweza kufikiwa
Wacha tujaribu chaguo jingine la kutumia REJECT:
iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with icmp-host-unreachable
Mteja hutoka baada ya sekunde na hitilafu [Errno 113] Hakuna njia ya kuwakaribisha, tunaona katika trafiki ya ICMP Kipangishi cha ICMP 127.0.0.1 hakiwezi kufikiwa.
Unaweza pia kujaribu vigezo vingine vya REJECT, na nitazingatia haya :)
Kuiga muda wa ombi kuisha
Hali nyingine ni wakati mteja aliweza kuunganisha kwenye seva, lakini hawezi kutuma ombi kwake. Jinsi ya kuchuja pakiti ili uchujaji usianza mara moja? Ikiwa unatazama trafiki ya mawasiliano yoyote kati ya mteja na seva, utaona kwamba wakati wa kuanzisha uunganisho, bendera za SYN na ACK pekee hutumiwa, lakini wakati wa kubadilishana data, pakiti ya mwisho ya ombi itakuwa na bendera ya PSH. Inasakinishwa kiotomatiki ili kuepuka kuakibisha. Unaweza kutumia maelezo haya kuunda kichujio: itaruhusu pakiti zote isipokuwa zile zilizo na bendera ya PSH. Kwa hivyo, uunganisho utaanzishwa, lakini mteja hataweza kutuma data kwa seva.
DHAMBI
Kwa DROP amri ingeonekana kama hii:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j DROP
Zindua mteja na uangalie trafiki:
Dampo la trafiki
[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
Tunaona kwamba muunganisho umeanzishwa na mteja hawezi kutuma data kwa seva.
KATAA
Katika kesi hii tabia itakuwa sawa: mteja hawezi kutuma ombi, lakini atapokea ICMP 127.0.0.1 tcp bandari 12345 haipatikani na kuongeza muda kati ya uwasilishaji upya wa ombi kwa kasi kubwa. Amri inaonekana kama hii:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT
KATAA kwa kuweka upya tcp
Amri inaonekana kama hii:
iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT --reject-with tcp-reset
Tunajua tayari wakati wa kutumia --kataa-na tcp-reset mteja atapokea pakiti ya RST kwa jibu, kwa hivyo tabia inaweza kutabiriwa: kupokea pakiti ya RST wakati unganisho umeanzishwa inamaanisha kuwa tundu limefungwa bila kutarajia kwa upande mwingine, ambayo inamaanisha kuwa mteja anapaswa kupokea. Muunganisho umewekwa upya na programu zingine. Wacha tuendeshe hati yetu na tuhakikishe hii. Na hii ndio trafiki itaonekana kama:
Dampo la trafiki
[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
KATAA na icmp-host-isiyoweza kufikiwa
Nadhani tayari ni dhahiri kwa kila mtu jinsi amri itakavyoonekana :) Tabia ya mteja katika kesi hii itakuwa tofauti kidogo na hiyo kwa KATAA rahisi: mteja hataongeza muda kati ya majaribio ya kutuma tena pakiti.
[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
Pato
Sio lazima kuandika mzaha ili kujaribu mwingiliano wa huduma na mteja aliyepachikwa au seva; wakati mwingine inatosha kutumia huduma za kawaida zinazopatikana kwenye Linux.
Huduma zilizojadiliwa katika kifungu zina uwezo zaidi kuliko ilivyoelezewa, kwa hivyo unaweza kuja na chaguzi zako mwenyewe za kuzitumia. Binafsi, huwa ninayo ya kutosha ya yale niliyoandika (kwa kweli, hata kidogo). Ikiwa unatumia huduma hizi au zinazofanana katika majaribio katika kampuni yako, tafadhali andika jinsi hasa. Ikiwa sivyo, basi natumai programu yako itakuwa bora ikiwa utaamua kuipima katika hali ya shida za mtandao kwa kutumia njia zilizopendekezwa.
Chanzo: mapenzi.com