OSPF Packet Formats

March 23, 2011 By Leave a Comment

I briefly wrote about OSPF previously. As we saw OSPF packets are encapsulated in the IP Packets with protocol number 89. But how does OSPF establishes adjacency and how does it exchanges the Database? The process is part of another post. But before we go into those details, we must first know how the OSPF packets look like. This will give us an insight of what information they carry and later we can put all these pieces together and get to know when and why each of these packet contents are used?

So first what are the various types…

Filed Under: OSPF

Convergence Time for RIP

March 22, 2011 By Leave a Comment

You will usually read everywhere that RIP takes considerably a large time to converge. But have you ever wondered why or did you try to find out what processes are involved due to which this delay occurs? I am sure quite a few of you have done it, but it always helps to refresh your memory :) Today we will see 2 scenarios and check the approximate convergence time it takes for RIP. The 2 scenarios are:

When a link goes down, an update is triggered with a poisoned route.
When the routing updates stops (like in…

Filed Under: RIP

Understanding RIP Timers

March 19, 2011 By 3 Comments

In my introductory post on RIP, I briefly talked about RIP Timers. It is quite easy to understand the timers but I do get confused sometimes when I have to debug some error quickly in a RIP network. I get confused easily between Invalid and Update timer. So today I am going to discuss briefly about how the timers work in RIP.

We will use the following topology for the explanation.

We will be using 4 routers connected as above. The interfaces connected and the their IP addresses are mentioned in the figure. Configuring RIP is…

Filed Under: RIP, Tutorials

Stepping into OSPF

March 17, 2011 By 1 Comment

Lets jump into OSPF today and get to know few basics. OSPF stands for Open Shortest Path First. It is classified under IGP group of protocols. It is an example of a link-state routing protocol. Specifically the name of the algorithm used in OSPF is Dijkstra’s Algorithm. We will talk about it in a later post. The major way of functioning of a Link State Protocol (and hence OSPF), is exchanging the topology information using the “link states”. The link state implies that we include information about the link as well as the current state of the link. All the link states together form the Link State Database (LSDB).

Let me point out the steps into enabling and running OSPF in a network:

Filed Under: OSPF

Introduction to RIP

March 15, 2011 By 1 Comment

One of the simplest routing protocol is Routing Information Protocol (RIP). It is classified as an IGP and it uses the distance-vector algorithm. Specifically the algorithm is called Bellman-Ford Algorithm. I will discuss the algorithm in a later post. Today I will describe briefly about the protocol and how it works. The protocol has 2 versions RIPv1 and RIPv2. Both are in use today and have significant differences. RIP has also been adapted for IPv6. This is called RIPng. RIP uses UDP to transmit its updates. The UDP port used is 520. RIP neighbors exchange their complete routing table at regular interval of 30 seconds (default). This is called the update timer. There is no session formation between RIP neighbors. Once RIP is enabled on a network subnet, it immediately starts

Filed Under: RIP