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The purpose of the PTR reverse address parsing is to reverse the domain name from the IP address, but in fact, not all IP addresses define PTR records, so PTR queries may fail. Look down, the last four packs are the normal ICMP requests and responses, and their delays are calculated based on the timestamp and 30ms.
![apt-get install tcpdump apt-get install tcpdump](https://www.usessionbuddy.com/static/snapshots/tcpdump_capture_packets.png)
Carefully observe their time, you will find that these two records are issued 5S before the next network package, the two PTR records consume 10s. Because we only see the request package, there is no answer package. Subsequent two reverse addresses parse the PTR request, it is more suspicious.
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#Apt get install tcpdump update
RUN apt-get update & apt-get install -y tcpdump & apt-get upgrade -y. Indicates the domain name to be queried.Īrticles 3 and 4, are ICMP Echo Request and ICMP Echo Reply, the timestamp of the response package 14: 02: 31.539667, minus the timestamp of the request package 14: 02: 31.508164, you can get, this time ICMP time 30ms 30ms. Optionally build you own tcpdump container. 114.114 A record request, in this TCPDUMP output:ģ6909+ represents the query identifier value, which will also appear in the response, the plus sign indicates that the recursive query is enabled. The first one is sent from the local IP to 114.114. Done The following extra packages will be installed: libpcap0.8 The following NEW packages will be installed: libpcap0.8 tcpdump 0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded. 3.4: ICMP echo reply, id 4356, seq 3, length 64 Here's the response: Code: Reading Package Lists. Listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytesġ4: 02: 31.100564 IP 172.16. To install tcpdump on Debian-based distributions such as Ubuntu: sudo apt-get install tcpdump.
#Apt get install tcpdump full
Tcpdump: verbose output suppressed, use -v or -vv for full protocol decode