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Simulans network problems in Linux

Salvete omnes, meum nomen est Sasha, testor in FunCorp duco. Nos, ut multi alii, architecturae muneris ordinati. Ex altera parte, hoc opus simpliciorem reddit, quia... Facilius est singula opera singillatim probare, sed contra, opus est mutuam operam inter se probare, quod saepe in retiaculis occurrit.

In hoc articulo, de duabus utilitatibus loquar quae ad reprimendas missiones fundamentales adhiberi possunt, qui operationem applicationis coram retis quaestionibus describent.

Simulans network problems in Linux

Simulantes network problems

De more, programmatio probata est in ministris testium cum bono interreti nexu. In ambitus productionis dura, res tam levis non potest esse, ut interdum programmata in condicionibus nexibus pauperis experiri debes. De Linux, utilitas adiuvabit munus simulandi huiusmodi condiciones tc.

tc(abbr. a Aenean Imperium) permittit te transmissionem configurare in systematis retis fasciculis. Haec utilitas magnas facultates habet, de illis plura legere potes hic. Pauca tantum hic considerabo: nos interest mercaturae schedulingarum, quibus utimur qdiscet quoniam opus est retis instabilem aemulari, incomptis qdisc utemur netem.

Sit scriptor resonare launch servo in calculonis servi (ego" nmap-ncat):

ncat -l 127.0.0.1 12345 -k -c 'xargs -n1 -i echo "Response: {}"'

Ut singillatim omnia momenta in singulis gradibus commercii inter clientem et ministratorem proponerem, simplex Python scriptionem scripsit quae petitionem mittit. Test nostro resonare servo.

Clientem source code

#!/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

Mittamus eam et inspiciamus negotiationem interface lo portusque 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

Negotiationis TUBER

[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

Omnia signa sunt: ​​triplex handshake, PSH/ACK et ACK in responsione bis - haec est commutatio petitionis et responsionis inter clientem et servitorem, et FIN/ACK et ACK bis - nexum complens.

mora packet

Nunc moram ad 500 milliseconds constituamus:

tc qdisc add dev lo root netem delay 500ms

Clientem demittimus et videmus scripturam nunc decurrere pro 2 secundis secundis:

[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

Quid est in negotiatione? Intueamur:

Negotiationis TUBER

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

Videre potes exspectationem pigriciam dimidiae secundae apparuisse in commercio inter clientem et ministratorem. Systema multo magis interestingly si pigri maior est agit: nucleus TCP aliquas resecare incipit facis. Moram mutemus secundae 1 et vide negotiationem (non ostendo huius output, expectata 4 seconds in tota duratione);

tc qdisc change dev lo root netem delay 1s

Negotiationis TUBER

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

Ex his constare potest, clientem bis syn/ACK misisse, minister bis SYN/ACK misit.

Praeter valorem constantem, mora ad declinationem, distributionem functionem et rationem (cum valore pro fasciculo praecedente constitui potest). Hoc ita fit;

tc qdisc change dev lo root netem delay 500ms 400ms 50 distribution normal

Hic moram inter 100 et 900 milliseconds constituimus, valores secundum distributionem normalem eligentur et cum valore morae pro priori fasciculo erunt 50% reciproci.

Ut notavi in ​​primo imperio eram adde: А Π·Π°Ρ‚Π΅ΠΌ recensere. Harum mandatorum significatio perspicua est, ideo plus adjiciam delquae ad figuram removendam adhiberi possunt.

Packet Loss

Nunc conemur facere damnum fasciculum. Ut ex documentis videri potest, hoc tribus modis fieri potest: amissis fasciculis passim cum aliqua probabilitate, adhibito Markov catena de 2, 3 vel 4 civitatibus ad damnum fasciculum computandum, vel exemplar Elliott-Gilberti utens. In articulo primum modum (simplicem et notissimum) considerabo, et de aliis legere potes hic.

L% damnum facis cum ratione 50% faciamus:

tc qdisc add dev lo root netem loss 50% 25%

Infeliciter, tcpdump evidenter nobis ostendere non poterit iacturam facis, nos solum id revera operatur. Et auctum et instabile tempus scriptionis cursus adiuvabit ut hoc verificetur. client.py (protinus absolvi potest vel fortasse in 20 secundis), tum numerus auctus retransmissus facis:

[user@host ~]# netstat -s | grep retransmited; sleep 10; netstat -s | grep retransmited
    17147 segments retransmited
    17185 segments retransmited

Addere sonitus facis

Praeter damnum ad fasciculum, damnum fasciculum simulare potes: strepitus temere positio apparebit. Damnum faciamus fasciculum cum probabilitate L% et sine ratione;

tc qdisc change dev lo root netem corrupt 50%

Currimus scriptor clientis (nihil interest ibi, sed accepit 2 seconds ad perficiendum), at negotiatio:

Negotiationis TUBER

[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

Videri potest quod aliquae fasciculi identidem missi sunt et est unus fasciculus metadata fracta; optiones [nop, unknown-65 0x0a3dcf62eb3d,[malae opt]>. Praecipuum autem est quod in fine omnia recte operata sunt - TCP coped with its task.

duplicatio fasciculum

Quid est aliud facere potes? netem? Exempli gratia, simulare condicionem adversam fasciculi iacturae duplicationis fasciculi. Hoc praeceptum etiam 2 argumenta sumit: probabilitas et relatio.

tc qdisc change dev lo root netem duplicate 50% 25%

Mutato ordine packages

Sacculos miscere duobus modis potes.

Primo statim mittuntur aliquae fasciculi, reliquae cum certa mora. Exemplum ex documentis;

tc qdisc change dev lo root netem delay 10ms reorder 25% 50%

Probabiliter 25% (ac ratione 50%) fasciculus statim mittetur, reliqui cum mora 10 millium secundorum mittentur.

Secunda methodus est, cum omnis Nth fasciculus statim data probabilitate (et correlatione mittitur), reliqua cum data mora. Exemplum ex documentis;

tc qdisc change dev lo root netem delay 10ms reorder 25% 50% gap 5

Quinta sarcina quaelibet 25% casum mittendi sine mora habet.

Mutatio Bandwidth

Plerumque ubique referunt ad TBFsed ope netem Mutare etiam potes latitudinem interfaciei;

tc qdisc change dev lo root netem rate 56kbit

Hoc quadrigis faciet treks circum localhost ut dolore superficies per Internet per horologio-sursum modem. Praeter bitrate ad occasum, nexum tabulatum protocollum aemulari potes exemplar: caput pro fasciculo pone, magnitudinem cellae, caput pro cellula. Hoc enim simulari potest machina argentaria and bitrate 56 kbit/sec:

tc qdisc change dev lo root netem rate 56kbit 0 48 5

Simulans nexu timeout

Alia res magni momenti in consilio probato cum programmatum accipiendo timeouts est. Hoc magni momenti est, quod in distributis systematibus, cum una officia debilitata sunt, alia debent ad alios tempore recidere vel errorem clienti reddere, et nullo casu simpliciter pendent, exspectantes responsionem vel nexum. institui.

Plures modi sunt hoc facere: exempli gratia, ficto utere quod non respondet, aut processui utens debugger coniunge, punctum in loco recto pone et processum siste (forsitan perversissimum est). Sed unum manifestissimum est portuum vel exercituum firewall. Hoc nos adiuvabit iptables.

Pro demonstratione, firewall port 12345 faciemus et scriptam clientelam nostram curremus. Firewall out of the packets ad hunc portum potes mittere aut ineuntes in accipientem. In exemplis meis, fasciculi ineuntes inflammati erunt (catenam INPUT et optioni utimur --dport). Tales fasciculi possunt esse STILLO, REIECTO vel REIECTO cum vexillo TCP RST, vel cum exercitu ICMP impossibile (immo, defectus habitus est. icmp-portum, impossibileet est etiam facultas respondendi mittendi icmp-rete-reaachable, icmp-proto-imreachable, icmp-net prohibitorum ΠΈ icmp-hospes prohibitus).

STILLO

Si regula est cum RORO, fasciculi simpliciter "abeunt".

iptables -A INPUT -p tcp --dport 12345 -j DROP

Clientem demittimus et videmus eum in scaena connexionis cum servo constringi. Intueamur negotiatio:
Negotiationis TUBER

[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

Ex his constare potest, clientem emittere SYN fasciculis cum exponentially timeout crescentem. Sic parvam bug in cliente invenimus: methodo uti debes settimeout ()circumscribere tempus quo clienti coniungere conabitur servo.

Nos statim regulam removemus;

iptables -D INPUT -p tcp --dport 12345 -j DROP

Potes omnia praecepta simul delere:

iptables -F

Si Docker uteris et firewall omnia negotiatio ad continens debes, tum hoc modo facere potes:

iptables -I DOCKER-USER -p tcp -d CONTAINER_IP -j DROP

REPROBO

Addamus nunc similem regulam, sed cum REJECTO:

iptables -A INPUT -p tcp --dport 12345 -j REJECT

Cliens exit post alterum cum errore [Errno 111] Connection noluerunt. Intueamur ICMP negotiationis:

[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

Ex his videri potest quod bis accepit clientem portum impossibile ac deinde errore finita.

REJECTO cum tcp-reset

Lets 'optionem experiri addere --reject-cum TCP-reset:

iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with tcp-reset

In hoc casu statim error cliens exit, quia petitio prima primum fasciculum accepit:

[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

REJECTO cum icmp-hospes-impossibile

Experiri aliam optionem ad utens REIECTO:

iptables -A INPUT -p tcp --dport 12345 -j REJECT --reject-with icmp-host-unreachable

Cliens exit post alterum cum errore [Errno 113] Iter ad exercitum, videmus in ICMP negotiationis ICMP exercitum 127.0.0.1 impossibile.

Potes etiam alios parametros REJECTUM experiri, et ego has intendunt :)

Simulans petitionem timeout

Alia condicio est cum client coniungere cum servo potuit, rogationem autem mittere non potest. Quomodo facis colum ut eliquare non statim incipias? Si commercium cuiuslibet communicationis inter clientem et ministrum spectes, animadvertes cum nexum constituendum, vexilla tantum SYN et ACK adhibentur, sed cum data permutat, ultimam rogationum fasciculum vexillum PSH continebit. automatice installat ne buffering. Haec informationes uti potes ut filtrum creare potes: omnes fasciculos sinebit praeter eos qui vexillum PSH continet. Ita nexus instituetur, sed client notitias servo mittere non poterit.

STILLO

Nam Roroam hoc mandatum spectaret;

iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j DROP

Launch clientem et videte negotiatio;

Negotiationis TUBER

[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

Videmus nexum constitutum esse et clientem notitias servo mittere non posse.

REPROBO

Mores in hoc casu idem erunt: client rogationem mittere non poterit, sed accipiet ICMP 127.0.0.1 tcp portum 12345 impossibile est et auge tempus inter petitionem resubmissionibus exponentialiter. Praeceptum hoc spectat sicut hoc;

iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT

REJECTO cum tcp-reset

Praeceptum hoc spectat:

iptables -A INPUT -p tcp --tcp-flags PSH PSH --dport 12345 -j REJECT --reject-with tcp-reset

Iam scimus quod cum usura --reject-cum TCP-reset the client will receive an first packet in response, so the manners cannot be forecast: Accepting an RST packet while the connection is established means the nernon is ex improviso occlused on the other side, which means the client should receive. Connection reset a pari. Nostram scripturam curramus et hoc confirmes. Et hoc est quod negocii erit simile;

Negotiationis TUBER

[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

REJECTO cum icmp-hospes-impossibile

Opinor iam omnibus manifestum esse quod mandatum simile erit :) Mores huius in hac causa paulum diversus erit ab illo simplici REIECTO: client non augebit tempus inter conatus remittendi fasciculum.

[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

conclusio,

Non est necesse scribere fictum ad probandum commercium servitii cum cliente vel servo suspenso, interdum satis est uti normae utilitates in Linux inventas.

Utilitas, quae in articulo tractata est, plus facultatum habent quam descriptae sunt, ut cum aliquibus optionibus tuis utendi illis venire potes. Personaliter, semper satis habeo de iis quae scripsi, immo minus. Si his vel similibus utilitatibus in tuo collegio uteris, scribe quaeso quam exacte. Sin minus, spero fore ut programmata tua meliora fiant si id probare volueris in condicionibus retis problematum adhibitis rationibus utendi.

Source: www.habr.com