Archive

Archive for August, 2012

Basic OSPFv2 in depth

August 27, 2012 6 comments

OSPF is one of the core topics of the CCIE R&S lab exam and therefore one should be an expert at it before attending the lab exam.

 In this post I would like to explore OSPFv2 and especially how OSPF uses its algorithm to find the best path to a destination. I will try to cover most of the general OSFP topics such as basic configuration, types of LSAs, Path selection, External path selection with LSA Type 5, Default routing, Conditional Default Routing, the different types of Stub areas, Virtual-links, LSA Type 3 filtering and Prefix filtering with route-maps. I have to admit that this post is quite long 🙂

 For this post I will use the following topology:

IGP: OSPF

Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

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IPv6 Tunneling

August 20, 2012 3 comments

As I was doing a Vol2 workbook lab the other day I found out that even if I have learned IPv6 tunneling before I was unable to configure it properly. That is why I have decided to make a post on IPv6 tunneling and I will especially focus on the protocol 6to4 described in RFC 3056 which facilate the deployment of IPv6 over IPv4 networks through tunnels. I will also talk briefly of RIPng, EIGRPv6 and IPv6 MP-BGP.

 I will first talk about some static tunnel mechanisms and then I will explore 6to4 in more details. For this topic I will use the following topology:

IGP: EIGRP AS 100

Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

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EIGRP Unequal Cost Load Balancing

August 12, 2012 8 comments

In this Post I would like to explore Unequal Cost Load Balancing with EIGRP and particularly how we configure EIGRP in order to achieve load balancing. I will talk about the feasible distance, the metric weights, offset-list, the different methods we can use to change traffic sharing among multiple unequal Cost paths with EIGRP and I will finally quickly cover CEF load balancing.

 For this post I will use the following topology:

IGP: EIGRP AS 100

Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

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GLBP (Gateway Load Balancing Protocol )

August 9, 2012 6 comments

I will take a little break regarding Multicast 🙂 and this time I will talk about a First Hop Redundancy Protocol (FHRP) which is GLBP (Gateway Load Balancing Protocol).

I have decided to look deeper into GLBP as I am quite familiar with HSRP or VRRP but the other day I had to troubleshoot a network which was configured with GLBP and although I can easily configure it there are some mechanisms of GLBP that are still unclear to me. So let´s clear them out!

Gateway Load Balancing Protocol (GLBP) is one of the First Hop Redundancy Protocol you can use when configuring First hop redundancy gateway for your end hosts. GLBP is Cisco proprietary and the big advantage compare to HSRP and VRRP is that you can load balance between the different gateways without changing the default gateway on the end hosts as you would do with HSRP for example to achieve load balancing which results in an extra administrative burden.

 GLBP is composed of two components:

  • The Active Virtual Gateway (AVG) at the control plane
  • The Active Virtual Forwarders (AVF) at the data plane

The AVG responds to ARP requests sent by end hosts to the virtual gateway IP address, and replies with different virtual MAC addresses that correspond to different active virtual forwarders (AVFs).

The AVF are responsible for sending traffic destined to their Virtual Mac address which has been allocated to them by the AVG. Both the AVG and AVFs are redundant, i.e. if a primary physical router representing the AVG or an AVF fails, another physical router will take its role.

Let´s consider the following topology to demonstrate how GLBP works:

Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

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Basic Multicast part 3 – PIM Sparse Mode – Auto-RP

August 9, 2012 3 comments

Continuing with Multicast topic I will this time talk about PIM SM and Auto-RP. This post is the next part of the previous post called: “Basic Multicast part 2 – PIM Sparse Mode – Static RP” where I talked about how to configure PIM in Sparse Mode but I also explained and demonstrate the source registration process with the RP as well as SPT switchover.

 The topology I am going to use in this post will be the same as the one I used in the previous multicast post.

 Let´s consider the following topology:

Source: The multicast source 150.1.0.4 will be sending to multicast group 239.10.10.10 which is part of the administratively scoped addresses assigned by IANA which is for use in private multicast domains, much like the IP unicast range defined in RFC 1918.

 RP: The RP is R4 with IP: 4.4.4.4

MA: the mapping agent is R3 with IP 3.3.3.3

IGP: The IGP used is EIGRP

Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

 We saw in the previous multicast post on PIM SM with static RP that all multicast enabled router need to know the IP address of the RP in order to build the shared tree and signal the RP of the presence of eventual multicast receivers for a specific multicast group.

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Basic Multicast part 2 – PIM Sparse Mode – Static RP

August 5, 2012 4 comments

This is the second part of my previous topic about Multicast. This time I will demonstrate how PIM Sparse Mode works based on the same topology as the previous post.

Let´s consider the following topology:

Source: The multicast source 150.1.0.4 will be sending to multicast group 239.10.10.10 which is part of the administratively scoped addresses assigned by IANA which is for use in private multicast domains, much like the IP unicast range defined in RFC 1918.

 RP: The RP is R4 with IP: 4.4.4.4

 IGP: The IGP used is EIGRP

 Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

 As PIM Sparse Mode is a much wider topic than PIM Dense Mode I will start to talk about PIM Sparse Mode with static RP, than Auto-RP, Auto-RP listener and finally PIM BSR.

PIM Sparse Mode is based on the “pull model” or “explicit join” which use a combination of both a shared tree and a source-based tree. The RP is making the connection between the shared-tree (tree build down the Multicast receivers) and the source-based tree (tree built up to the source).

PIM Sparse Mode uses (*,G) entries to forward Multicast traffic unlike PIM Dense Mode. So the key difference between PIM Sparse Mode and PIM Dense Mode is that PIM Sparse Mode the forwarding state in the router is set up as a result of an explicit “join” where in PIM DM (PIM Dense Mode) the forwarding state is set up upon arrival of multicast traffic.

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Status update

August 5, 2012 1 comment

It has almost been 5 months since my last post on Multicast and that is a huge time not blogging. It is going so fast and although I have wished to make more posts I couldn´t have done it as I have been so busy with the CCIE training. This training is just incredible, I have spent more than 700 hours until now and it has just been crazy trying to stick to the study plan I have made in January when I started my journey! I am proud to say that I haven´t lost a single week until now which is quite good because I have also been busy with work.  I have missed a lot the fact that I couldn´t blog on some topics which I was not comfortable with but I just couldn´t do the training and blogging at the same time.

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