A few days ago i wrote about detecting ICMP tunnels. I came to the conclusion that for the two tunnels i tried the properties to detect on were:
- Non-standard average packet size. E.g. 81.81 bytes for the first connection is non-standard.
- Number of bytes in both directions are unequal.
- Average packet size in both directions is unequal.
I believe the third is the most important, because it must mean that 1 is also true and 2 is very likely to be true. If the average packet size is unequal in both directions, one of them should be non-standard. So far i have only seen echo-request and echo-reply being equal in size for pings. Unequal average packet sizes with exactly the same amount of data transfered is very unlikely, so i have ignored that for now.
This is the full report that shows all ICMP with unequal average packet sizes:
SUSPECTICMP||Suspect ICMP LAN->WAN: Top 10 ICMP users in the LAN talking to the WAN, with different packet sizes, with source and destination, volume and average packet size, sorted by packet size (fields: source ip, dest ip, from source MB, from source packet size, from dest MB, from dest packet size, total duration, average duration)||query||SELECT INET_NTOA(src_ip), INET_NTOA(dst_ip), my_src_bytes/1048576 AS my_src_mb, my_avg_src_pktsize, my_dst_bytes/1048576 AS my_dst_mb, my_avg_dst_pktsize, my_tot_duration, AVG(my_tot_duration) AS my_avg_duration FROM ( SELECT src_ip, dst_ip, ip_proto, SUM(src_bytes) AS my_src_bytes, SUM(dst_bytes) AS my_dst_bytes, start_time, end_time, SUM(src_bytes)/sum(src_pkts) AS my_avg_src_pktsize, SUM(dst_bytes)/sum(dst_pkts) AS my_avg_dst_pktsize, SUM(duration) AS my_tot_duration FROM ( SELECT sid AS my_sid, src_ip, dst_ip, ip_proto, src_bytes, dst_bytes, src_pkts, dst_pkts, start_time, end_time, duration FROM sancp IGNORE INDEX (p_key) WHERE ip_proto = 1 AND src_pkts > 0 AND dst_pkts > 0 AND start_time > %%STARTTIME%% AND end_time < %%ENDTIME%% ) AS step1_table INNER JOIN sensor ON my_sid=sensor.sid WHERE %%SENSORS%% AND ((src_ip between INET_ATON("192.168.0.0") and INET_ATON("192.168.255.255")) or (src_ip between INET_ATON("10.0.0.0") and INET_ATON("10.255.255.255")) or (src_ip between INET_ATON("172.16.0.0") and INET_ATON("172.31.255.255"))) and ((dst_ip not between INET_ATON("192.168.0.0") and INET_ATON("192.168.255.255")) and (dst_ip not between INET_ATON("10.0.0.0") and INET_ATON("10.255.255.255")) and (dst_ip not between INET_ATON("172.16.0.0") and INET_ATON("172.31.255.255"))) GROUP BY dst_bytes ) AS step2_table WHERE my_avg_src_pktsize != my_avg_dst_pktsize GROUP BY src_ip,dst_ip ORDER BY my_avg_dst_pktsize DESC, my_avg_src_pktsize DESC LIMIT 10||8||
This query only works on MySQL 4.1 and higher. It results in this report:
This detects all tunnels I had setup, and shows nothing of the other non-tunnel tests I did, like the ping flood.