This was a question i raised a while ago but never ended up getting round to creating an article. So as we know the basics of traceroute is that it sends out a bunch of UDP packets each packet with a TTL 1 higher then the previous one. When the hop receives the packet and … Read more
A floating route uses a higher preference to ensure that it is used a primary route. In the event of the floating route being removed from the routing table (due to Dynamic Routing or an Interface going down) the other route takes preference and is used. set route [dst ip]/[mask] vrouter [vr name] preference [perf]
When troubleshooting ADSL issues there are 2 tests that you can do to help you troubleshoot your problem. They are : Quiet Line Test Unplug any extension phones, extension cables, answer machines or fax.. Plug a normal touch tone phone directly into the BT master socket. Dial 17070, press option 2 (quiet line test) You … Read more
ADSL (Asymmetric Digital Subscriber Line) is a technology (method) for the transmission of data across a standard phone line. It does this by using frequencies that are not used by standard telephone calls. This is where the term “Broadband” comes from as a broad band of frequencies are used to transmit high speed data and … Read more
NAT-T (NAT Transversal) allows for IP-ESP packets to transverse devices which introduce NAT.The problem with IPSec is that it uses the IP-ESP protocol naively. The ESP protocol doesn’t have “port-numbers” like TCP and UDP so NAT does not know how to translate the traffic because NAT/PAT is based on port numbers. With NAT-T the ESP … Read more
In this article we will be covering SSH port forwarding also known as SSH tunneling. As previously discussed in our previous article Proxing Web Traffic across a SSH Tunnel using SSH Dynamic Port Forwarding, SSH port forwarding (or tunneling) re-routes TCP/IP connections through an established SSH connection. Being encapsulated within SSH provides security benefits along … Read more
SSH port forwarding (or tunneling) re-routes TCP/IP connections through an established SSH connection. Being encapsulated within SSH provides security benefits along with the ability to route traffic through firewalls using just port 22 (SSH). In this example we will proxy our web traffic via our remote server across an established SSH connection. This is achieved … Read more
URG This flag indicates that the packet contains urgent data that should be processed as soon as possible. This flag is used to provide two virtual channels within one TCP connection. The URG flag is also known as out-of-band. This is usefful for a sender to present data that can overtake any bytes queued … Read more
Instant Messaging is a Global Communications Medium for Business and Consumers. 85% of organizations report that they use IM for business usage and there are a reported 400 million global IM users.IM though does present a number of security issues. Unprotected IM is vulnerable to viruses and spam. In addition to this its ability to … Read more
SMTP is an Application layer protocol (RFC 821,1982). Being a completely ASCII text based communication protocol, any binary or not text based attachments must be encoded before it can be sent using SMTP. To allow users to send rich content is MIME (Multipurpose Internet Mail Extension) was introduced. MIME is an Internet standard that extends … Read more
Who are Akamai ? Akamai Technologies was founded in 1998 to provide a distributed computing platform for global Internet content and application delivery. The word Akamai in Hawaiian means smart or intelligent. Akamai has developed a global array of interconnected servers that cache content supplied by its Internet customers. This way the content is physically … Read more
File Transfer Protocol (FTP) is a network protocol used to transfer data from one computer. In order to download and upload files to an FTP site, you need to connect using an FTP client/server. FTP runs exclusively over TCP and listens on port 21 (command port) by default. Data is transferred across a separate data … Read more
This is by no-means a full guide to MTU or PMTU but a small collection of notes. Protocol Overhead VLAN Tag (Dot1q) 4 Bytes MPLS 4 Bytes IP 20 Bytes TCP Header 20 Bytes UDP Header 8 Bytes ICMP Header 8 Bytes Example To send a ping with a full 1500 byte packet , you … Read more
DNS servers are based on a recursive look up as you can see below. Below you can see XP forwarding the request to its DNS server. The DNS Server then recursively resolves the DNS request. Once it has the answer to the Clients request, it forwards the answer back to the client. A great tool … Read more
Below is a reference for the various cabling connectors, Fibre LC (Local Connector) F Type MT-RJ SC (Standard Connector) ST (Straight Tip)
In application software v6.0 and later, the Rapid Spanning Tree Protocol (RSTP) replaces the 802.1D Spanning Tree Protocol (STP). STP is pretty slow at recovering from a failure in the network. RSTP was created to decrease this recovery time. When a switch is running RSTP, a port can change from blocking to forwarding more quickly … Read more
The Cisco Discovery Protocol (CDP) is a proprietary layer 2 network protocol developed by Cisco Systems that runs on most Cisco equipment and is used to share information about other directly connected Cisco equipment such as the operating system version and IP address. Globally (config)# cdp run(config)# no cdp run Interface To disable, (config-if)# no … Read more
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