Slow file transfers must be really bothering everyone. I have a ZyXEL NSA325 NAS device which has a gigabit interface but I am getting extremely low throughput. Unfortunately this has been a problem I think since I bought this device. Now I could finally get hold of time to troubleshoot the issue. Here is my
Read More »
Path MTU discovery that is in place today is relying on ICMP based MTU discovery i.e you send an oversize packet which can’t be forwarded by an intermediate host in the path because the next hop link has a lower MTU size, then the source host is notified by this hop which can’t forward this
Read More »
TCP sliding window is very crucial concept in understanding how TCP behaves. In order to see how this mechanism works, I have rate limited an HTTP download and observed what happens during this scenario in which we will see reports from Wireshark that [TCP Window Full] and [TCP ZeroWindow]. The aim of this post is
Read More »
Van Jacobson is a prominent person in networking, especially for TCP/IP. What I didn’t know was (according to wikipedia) original traceroute was also written by him. As this tool is the swiss knife of a Tech Support Engineer, I would like to share the meaning of some of the outputs. If you have any other
Read More »
Traceroute is a great tool to discover the path a packet traverses in outgoing direction but if you have an MPLS cloud, you may have some unexpected behavior if you don’t do some tweaks. First of all let’s see how traceroute discovers a path when there isn’t any MPLS cloud. The network above is using
Read More »
On this Saturday evening, I have finally completed my work with TCP SACK analysis. This post was in my mind for sometime but now I have done it after building my big local Internet at home. You will also find some stuff about receive segmentation offload, wireshark tips etc. Here is the topology used for
Read More »
I couldn’t really find a suitable topic for this post actually but I will try to find answers for the following questions: How can we fragment an IP packet manually in scapy How does a fragmented packet look like and how the transport layer (TCP/UDP) header is located How do we forward fragmented packets, do
Read More »
I must say that network troubleshooting is not an easy task. Especially if you need to analyze thousands of packets in packet captures or lines of flow traces. IP ID is a field I use to compare captures taken at different segments most of the time. Also it is a crucial field for me to
Read More »
In my previous ipsec troubleshooting post, I haven’t talked about how we approach performance issues. Which is probably not a JNCIE-SEC topic but this is a very important topic for the real networks. In this topology I will examine how throughput changes between two end points of an IPSEC tunnel depending on the configuration of
Read More »
Python is a great tool to do some socket operations. I have written a piece of code by which I can scan a port range. It is very basic and missing bunch of checks as aim is the simplicity here. #!/usr/bin/python import socket,sys try: sys.argv[3] except: print "Usage: port_scanner.py [hostname|IP] [port_start] [port_end]" sys.exit() host =
Read More »
You must be logged in to post a comment.