Router UDP NAT Bug Tester

By: Sad Pencil

This program sends multiple DNS queries to 8.8.8.8 in parallel with the same UDP sender ports and expects to receive all the answers. It is useful to test whether the NAT gateway is buggy and causes DNS lookup timeouts for Linux devices. See Racy conntrack and DNS lookup timeouts for technical details.

This program is able to send two packets within 10,000 nano seconds, to reliably reproduce the bug.

Compile

make

Usage

./client -n <thread-num> -d <domain-name> -s <name-server> 
./client -n 2 -d www.google.com -s 8.8.8.8

Examples

$ ./client
Thread 0 sent a DNS query.
Thread 1 sent a DNS query.
Thread 1 received a DNS answer with 48 bytes. Time: 17 ms.
Thread 0 received a DNS answer with 48 bytes. Time: 17 ms.
# note: two packets arrives successfully

$ ./client
Thread 0 sent a DNS query.
Thread 1 sent a DNS query.
Thread 0 received a DNS answer with 48 bytes. Time: 17 ms.
^C # note: the second packet can't arrive, indicating the bug of the NAT gateway

Acknowledgment

This project is modified from a dns client at uberj/DNS-Client.