Category: Network Fundamentals

What is route recursion

We are going back to networking basics with this post. In few lines below you will find most important theory that makes network gear do its job.

The main router job is to making routing decisions to be able to route packets toward their destination. Sometimes that includes recursive lookup of routing table if the next-hop value is not available via connected interface.

Routing decision on end devices

Lets have a look at routing decision that happens if we presume that we have a PC connected on our Ethernet network.

If one device wants to send a packet to another device, it first needs to find an answer to these questions:

  • Is maybe the destination IP address chunk of local subnet IP range?
    • If that is true, packet will be forwarded to the neighbour device using Layer 2 in the ARP example below.
    • If that is not the case, does the device network card configuration include a router address through which that destination can be reached? (default gateway)
  • Device then looks at his local ARP table. Does it include a MAC address associated with the destination IP address?
    • If the destination is not part of the local subnet, does the local ARP table contain the MAC address of the nearest router? (MAC address to IP address mapping of default gateway router)

Proxy and Reverse Proxy Server

This will be a short Reverse Proxy Caching Overview that will explain what proxy is and what is reverse proxy all about.

Normal proxy cache topology is one where the server called proxy server will be some kind of intermediate device between client and server. Proxy will receive all requests from clients and it will forward those requests to servers. The clients will think that the proxy is really the server with the content and the server will think that the Proxy is really the client asking for some resources. Proxy server is used to intercept the communication from client and evaluate the request or control the request for security reasons. On other side clients are sometimes using proxy servers to hide their identity and location because server will only see the location and IP address of proxy server and it will think that that is really the client.

We can say, normal proxy is when proxy server is proxy for clients.

In the reverse proxy, the reverse proxy server acts as a proxy for the server.

Reverse proxy is used for replication of content to different far locations and in other case for replication of content for load balancing.

Wildcard mask – What’s the difference from subnet mask?

What is Wildcard Masking?

Wildcard mask is like any other computer IP address basically a group od zeroes and ones (o and 1). To be short, in wildcard mask all number one (1) mean “I don’t care about that position”, and all zeroes (0) mean “I care about that position in binary address”. Let’s take an example where Access list with wildcardmask will be able to deny fourth subnet and alow next four and so on for all /24 subnets of supernetwork.

In the access-list we put an network;

We know that 255 means 1111 1111 in binary.
We know that 251 means 1111 1011 in binary.

In the line we could change to any other kind of because in this situation our ACL will not care about the bits in the first, second and last octet. We could write it will fit in our example.

One more thing to make myself more clear. If we use deny in ACL, this ACL will not filter only network, but every network in the whole 32bit range from to in which third octet has an zero (0) in 6th position. To filter only those subnets that are part of supernet we would need to use deny because in that way we will say that we care about first and second octet of the address.


VoIP and IP telephony – Defining Basics of Voice

VoIP and IP telephonyDefining Basics of Voice, VoIP and IP telephony

Confusion has come along with the associated taxonomy of VoIP technology and IP telephony.  Both of them refer to use the same IP network to send voice messages. But the main difference between VoIP and IP telephony is that VoIP is connecting old fashion analog phones to specific gateway device who are able to convert analog voice data into digital bits and send them across the internet bypassing the expensive PSTN telephone networks. In the case of IP telephony the phones by them selves are digital devices and they are made to record the users voice directly into digital signal and send it across IP network using special Communication manager devices that are enabling this technology to work. IP telephony technology resides on IP network and natively uses the IP network for communication.

IPv6 Day – 6 June 2012.

World IPv6 dayInternet Society is organizing today 6 of June 2012 the World IPv6 Launch. This will not mean that we will close the Internet on the IPv4 protocol and transfer it to IPv6. It will also not mean that everyone needs to make the transition today. Most of you reading this is already ready to use IPv6. Most of modern computers are able to manage and configure they network interface cards (NIC) to both IPv4 and IPv6 addresses. But what is then IPv6 launch day? Big and important websites and Internet Service Providers participate in today’s day in the way that they will begin the transition from IPv4 and permanently enable IPv6.