OSPF Prefix Suppression

Recently I came across this command "ip ospf prefix-suppression". It's a nice feature which allows the suppression of the transit link advertisement which will result in smaller RIB. 

Let's look at the below topology and see how it works.

We have R1, R2 and R3 connected with ethernet interfaces. All three routers are running OSPF process 10. I have applied the command "network 0.0.0.0 255.255.255.255 area 0" on all of them. 

DNS Records

In this post we are going to look at various DNS records which are frequently used.

1. A Record

The A (Address Record) record maps the domain name to the 32 bit IP address so for example 

www.mydomainname.com. A 192.168.1.1

The A record is also known as host record.

For the IPv6 you have AAAA record which directs the domain name to the 128 bit IP address. The structure is very much the same; it's just bit longer.

Load Balancing using BGP Communities

In this post we will look at how we can achieve load-balancing using the BGP communities. 

Community values are similar to the "tag" we use in IGP. They are used to group the prefixes. When the neighbour receives the prefixes, it will examine the community value and take an action such as filtering or modifying the BGP attributes.

We are going to use the below topology for our experiment.

BGP Redundant Route-Reflectors

In this post we will look at the various ways to configure redundant route reflectors in the network.

As shown in the diagram, R1 and R2 are the route-reflectors, R3 and R4 are the RR-Clients & R5 and R6 are the non-clients. All the routers have IGP reachability to each other. I have used their loopback interfaces to establish IBGP neighborship. 

BGP Maps - Part 3

7) Inject Map:-

To understand inject-map, let's look at the scenario shown in the diagram.

We have four routers, each in different BGP AS. They have EBGP neighbourship with directly connected peer. From R1, we are advertising 192.168.1.0/24 subnet and it's visible on R4 via two paths.

BGP Maps - Part 2

Continuing from our last post, we will now see how Exist Map and NonExist Map works.

5) Exist Map:-

Let's look at the scenario shown in the diagram below.

The users are connected with router R1 and they need to access the servers in the DC. R4,R2 and R1 have EBGP neighbourship between them. 
R4=AS40
R2=AS20
R1=AS10

BGP Maps - Part 1

Today we will look into various maps available in BGP. 

Here is the list which I am aware of

1)Suppress Map

2)Unsuppress Map

3)Advertised Map 

4)Attribute Map/Route Map

5)Exist Map

6)NonExist Map

7)Inject Map

8)Table Map

We will go through each of them one by one. 

1) Suppress MAP:-

 We are going to use the below given topology.

Different methods to advertise a default route in BGP Part 3:

In this post, we’ll go through the 3^rd method to advertise a default route in BGP.

I’ve removed the neighbour x.x.x.x default-originate command.

3^rd method: Using default-information originate command (after redistributing the static route in BGP)

I’ll first create a default static route.

Above is the output from R1s routing table confirming that there is a static default route entry.

Now, I’ll redistribute this static route into BGP.

 

Different methods to advertise a default route in BGP Part 2:

Now let's go through the 2nd method to advertise a default route in BGP.

Method 2: Using default-originate command in the neighbor statement

I’ve removed the default static route from R1 which removes the default route on R2 and R3 dynamically.