When troubleshooting this condition, it is imperative that you obtain a thread dump on the client. There is a reason it cannot consume the data being sent to it from the server, so you need to understand why it is…
Category: Networking
Can two switches talk to each other?
Yes, and you don’t even need a crossover cable for the connection on newer switches. One important proviso is that this can be only on the default VLAN. If you use a different VLAN, the mode must be trunk rather…
Getting window size from raw packet capture
tcpdump shows the unscaled window size. It is important to note that the value of wscale is not the value by which to multiply, it is the bits that are set on the scaling factor, as it uses binary math.…
wireshark, python, and Excel for graphing TCP window sizes
Filter the packets in which you are interested. In this case, we filter on the source IP… …then export the packets to a CSV file… …which we then parse in python to produce another CSV file… f = open(“good.csv”,”w”) for…
Can hosts in same subnet ping each other if in different VLAN’s?
Short and sweet, no! In the example above, Laptop0 and Laptop2 are in VLAN1, while Laptop1 and Laptop3 are in VLAN2. We apply the same network and subnet mask (192.168.1.1 and 255.255.255.0) to each VLAN. We assign the Laptop’s address…
Simple network test with client and server
This simple network trace shows the essential elements of a network interaction between a client and a server. For our test, we use the following for the client… import sys, socket, time remote_ip = socket.gethostbyname(socket.gethostname()) s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) #s.setsockopt(socket.IPPROTO_TCP,…
Spoofed IP network behaviour
In this case, we spoof the IP of our client to 192.168.1.101. When we do this, and send only a SYN packet to the server, we see the SYN on the client… [root@cmhlcarchapp02 ~]# python spoof.py 1 09:37:52.469226 IP 192.168.1.101.49999…
Connection Reset – What does it mean?
Generally, it indicates your client successfully connected to the server. A subsequent attempt to use the client connection failed after the server closed the socket, or had been disconnected for any reason. You can prove this with what is below,…
Akamai GTM
Akamai’s Global Traffic Manager, or GTM for short, is technology that allows a user to configure traffic to be sent to more than one data center, or at least more than one origin URL. For an Akamai primer, go here.…
net.ipv4.ip_no_pmtu_disc and don’t fragment
We received an email asking that we restart a given server as the ATG lock manager had a required lock and a scheduled job could not move forward. I don’t like to do that without some triage. We were stuck…