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The word VRF stands for Virtual Routing and Forwarding, this feature is used to create multiple instances of the routing table on the same routing device. VRFs are usally used in conjunction with MPLS VPN to separate the traffic of multiple MPLS VPN customers. VRF Lite feature is part of Cisco’s network virtualization portfolio. VRF [...]

Everyone who ever studied BGP knows that BGP has strong precautions and rules for loop prevention. In this post I will focus on iBGP and specifcally route reflectors.
The rule states that any route received from an iBGP neighbor should not be advertised to another iBGP neighbor.
This loop prevention mechanism induces a requirement that all iBGP routers in [...]

The following example is showing how to use distribute-list with the gateway option for inbound route filtering  in OSPF. The diagram below shows R1 directly connected to R2 with OSPF configured between them.

Initial Configuration:
!– R1 OSPF configuration
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 172.16.12.1 0.0.0.0 area 0
network 172.16.101.1 0.0.0.0 area 0 !– R1’s Loopback0
network 10.10.10.1 0.0.0.0 [...]

BGP has multiple ways of advertising a default route to its neighbors;  the neighbor default-originate command is one of these methods and used to advertise a default route to a specific neighbor. Below are some characteristics of the default route advertised by this way.
Originator router:

Default route does not need to be existing in the routing [...]

If domain lookup is enabled (default) the router treats each mistyped command as a hostname and tries to resolve its IP address by querying the DNS server.
This behavior is undesirable in most cases because it wastes network administrators time waiting for routers trying to resolve mistyped commands.
R2#xyz
Translating “xyz”…domain server (255.255.255.255)

Translating “xyz”…domain server (255.255.255.255)
(255.255.255.255)
Translating “xyz”…domain [...]

This is a master piece post from Petr Lapukhov explaining Private VLANs; what are they ? and how to configure and troubleshoot them ?. I am sure you will never get confused by Private VLANs anymore.
Private VLANs revisited
Read and understand

After explaining how STP works to ensure your network is free of bridging loops in previous posts, we are going directly to a configuration example. We will use a simple topology in the diagram below and configure the switches to accomplish the tasks listed below.

Task1: Configure SW0 as a root bridge for both VLAN1,2.
For SW0 [...]

In the first post STP part1, we discussed the root bridge election process, that was the first step in calculating the spanning tree topology. Lets dive and explore step2.
Step2: Best Path selection
After choosing and agreeing on the root switch for the domain, each switch starts looking for the shortest path to the root of the [...]

As we mentioned in one of our previous posts, STP was developed to allow redundancy in the L2 network while maintaining a loop free network. Today we are going to discover how STP is actually doing this function.
Step1: Electing the root bridge
What is the root bridge?
The root bridge is the master bridge of the spanning [...]

In the first post we explored the basic configuration of BGP route aggregation with and without the summary-only keyword.
In todays post our task is to explore the suppress-map keyword using the same topology used in the first post. “please refer Part1 or the series for R1&R2 configuration and network diagram“.
Task1: Configure route aggregation on [...]