Introduction Reverse path forwarding (RPF) is a technique used in modern routers for the purposes of ensuring loop-free forwarding of multicast packets in multicast routing and to help prevent IP address spoofing in unicast routing. [1] Within this article, we will look at multicast RPF, and look into why it is needed along with how it … Read more
Introduction In order for OSPF-enabled routers to exchange information, they must form an adjacency (relationship) with their neighbor. Within this article, we will look at the process and various steps involved (Figure 1). Requirements Before the OSPF router even starts to try and form an adjacency, OSPF must know/determine the following: Router ID – The … Read more
Introduction IGMP (Internet Group Management Protocol) is a Layer 3 protocol (IP protocol number 2) and is a key component (Figure 1) to IP multicast. The role of IGMP is to notify a local multicast router when a host wants to receive multicast traffic for a specific group. Figure 1 – Summary of Multicast Components. There are 3 versions … Read more
Interface to Network Security Functions (I2NSF) is a working group within the IETF formed to define a set of interfaces and data models for monitoring and managing network security functions hosted across multiple sites. I2NSF states, Network security functions (NSFs) are provided and consumed in increasingly diverse environments. Users of NSFs could consume network security … Read more
Issues with Layer2 across DCs Ideally, data centers do not share fate. But extending L2 creates a common broadcast domain in 2 data center. Now, we are sharing fate Traffic patterns become sub-optimal Where does the default-gateway live? In the local DC? Or remote? Traffic to load balancer to pool member, but pool member lives … Read more
Unlike CDP, LLDP is a, non Cisco propriety, discovery protocol. LLDP is disabled by default. Global R1(config)# lldp run Timer/Holdtime lldp timer 5 lldp holdtime 15 Show R1(config)# do show lldp neigh
If you want to perform any form of packet analysis/reporting there is, really, only one program to use. Yep you guessed it, Wireshark. However as Wireshark is a GUI based program, it raised the question, How do you build a packet analysis report via the commandline ? Within this article we will show you 2 … Read more
The other day I was reading about the benefits and new features within HTTP 2.0. One of the key features to HTTP2.0 is the ability to interleave (i.e multiplex) multiple requests and responses across a single TCP connection. Resulting in Domain Sharding being considered counterproductive. However, based on how Domain Sharding and HTTP Pipelining can … Read more
Wireshark provides the ability to calculate the amount of time between packets. This data can then be used within the IO graphing tool of Wireshark to create a visual representation which can be used when troubleshooting networking issues. Within this article we will show you how to create the TCP delta column, the TCP preferences … Read more
Introduction Caching is one of the key optimisation methods in HTTP. It can reduce both network overhead and page load times, resulting in an improved experience for the client. Within this article we will look the various headers and options available in both HTTP 1.0 and HTTP 1.1. HTTP 1.0 The caching mechanism within HTTP … Read more
Wireshark offers a huge range of features, allowing you to display the data and results captured at the packet level. This article will show you how to graph the HTTP response times of your capture. i.e the time taken to receive the HTTP response once the HTTP request has been Acknowledged. Steps Goto ‘Statistics’ / … Read more
Content-Length The content-length header informs the client of the byte length of the HTTP body. This is typically used for HTTP 1.1 (i.e persistent connections) to ensure the client knows when the current response/request is complete so that the connection can be reused for further requests. Transfer-Encoding Chunked However in certain cirucumstances the server may … Read more
The Vary Header The vary header is sent within the servers response to the client and instructs any intermediary caches to cache a separate instance based on the headers specified within the vary header. Encoding Headers As our example is based around the following HTTP headers, here is a quick summary of each, Content-Encoding (HTTP … Read more
Within this article we will show you how to list all IP`s relating to a single AS. STEPS First of all get the IP address for the domain. [root@server]$ whois 173.252.110.27 | grep OriginAS OriginAS: AS32934 Finally run another whois against the AS to obtain a list of IPs. origin=$(whois `dig facebook.com +short | head … Read more
How can I optimize the throughput of a VPN across a WAN based link ? I was recently asked this question the other day by a client, after seeing the results (in which the transfer speeds were nearly tripled) I thought it would make an interesting article. Background My client had a VPN (Site to … Read more
NS (Name Server) Records are used within the Domain Name System (DNS) to determine which name servers are authoritative for a domain. NS records also provide name server delegation. Example Within this example we have a domain named example.com. The parent zone (.com) will contain the NS records for this zone. Now, if we wanted to … Read more
What is MTU ? When sending traffic across a network, computers use something called an MTU (Maximum Transmission Unit). This (network interface) setting dictates the size of the largest frame it can send across the network. Below shows the MTU default, Network MTU(Bytes) X.25 576 IEEE 802.3/802.2 1492 Ethernet 1500 FDDI 4352 Token Ring 17914 … Read more
1. INTRODUCTION The Spanning Tree Protocol (STP) is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation. 2. ROLES Spanning Tree defines 3 port roles. They are: Root Port Designated Port Blocking (Alternative Port) 3. … Read more
IPv4 is the current protocol used for sending data over the internet. The main issue with IPv4 is its limited address space. With the amount of available IPv4 address rapidly shrinking IPv6 overcomes this by introducing 128 bit addresses and a much larger address space to that of IPv4. 1. Changes Introduced by IPv6 Summary … Read more
The other day someone asked me to explain subnetting. It had been a while so I dusted off my CCNA books and attempted to answer his questions. So I thought this would be an ideal time to jot down some notes for future reference. This isnt a tutorial or guide but just some some notes … Read more
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