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orhanergun.net 2015 review

I’m proud to be the owner of the best computer network design blog and get positive feedbacks from users all over the world. In recent times, I have observed that everybody has been reading this blog. Because of this, I owe all the readers of this blog my achievements. Indeed, your comments and post views have encouraged […]

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Single Vs. Dual Carrier Design

Companies don’t always have high availability. What’s more, there is always a concern of budget and complexity with the high availability even though a number of factors need to be considered during network design. If the applications of the company do not require high availability, dual carrier or two links to the same carrier is not […]

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CCDE – Review Of CCDE Practical Workbook By Orhan Ergun

To kick off the new year, I will give you a review of the CCDE Practical Workbook by Orhan Ergun, CCIE #26567 and CCDE #2014:17.

Orhan is a friend and has provided the workbook to me for reviewing. I would like to make it clear that being a friend or providing a product for free does not give any leverage when I review a product. I always give my honest opinion when reviewing a product.

Orhan is a CCDE trainer running the website orhanergun.net and he writes and blogs a lot about network design. He has written a practical workbook to aid CCDE candidates in their studies for the CCDE practical.

As with any workbook for any exam, your expectations must be realistic before purchasing a product. You can only get as much out of a workbook as the effort you put into your studying. A workbook is not a complete solution that will be your only source of studying. You must do additional reading, and lots of it.

The CCDE practical workbook is divided into sections such as layer two, layer three, MPLS, BGP, multicast and so on. Each section starts with some introduction to each technology and Continue reading

IGP LDP Synchronization

I implore all my readers to always remember this topic: IGP LDP synchronization. It is important to use IGP LDP synchronization to avoid blackholing, especially when MPLS networks fails to function effectively.     In the topology above, IS-IS is running in the network of the service provider. For the transport label distribution or topmost label/tunnel label, […]

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Routing design

Understanding everything about routing design is no brainer, especially if you have the chart below on your wall. The table below highlights the pros and cons of each routing protocol. Of course, you need to consider the design attributes shown in Figure A before embarking on routing design. Should you like the comparison of the […]

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Dual Core Network Design

Dual core design, also known as dual plane or disjoint plane topologies, refers to a highly redundant network chosen by companies whose main objective is to improve the resiliency of their network. Created using different data planes, dual core design is implemented by companies that receive the service from the different service providers. Put simply, […]

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DMVPN point-to-point GRE and mGRE

DMVPN spokes can use either point-to-point GRE tunnels or multipoint GRE tunnel interface. Recently, I received a question regarding DMVPN. In fact, the Reader asked me two questions: When is GRE used in network design? When is mGRE used in network design? Answering the aforementioned questions are the basics that you must know if you […]

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What is a micro loop in routing?

Micro loop can be found in fast-rerouted networks. Fast reroute, as a proactive convergence mechanism, provides sub-second data plane convergence. If there are technical glitches, upstream node sends the traffic through the repaired path to the downstream device. For the downstream node to be used as a backup/repair node, it should be loop-free. What do […]

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Segment Routing Fast Reroute

Segment Routing Fast Reroute  – Traffic Engineering with Segment Routing uses LFA mechanism to provide 50 msec fast reroute capability. Current Segment Routing implementation for the OSPF uses regular LFA (Loop Free Alternate) for fast reroute in Cisco devices. Because LFA (Loop Free Alternate) has topology limitations, it does not include many faulty scenarios. On the […]

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HSRP – VRRP – GLBP

HSRP, VRRP and GLBP are the three commonly used first hop redundancy protocols in local area networks and the data center.

In this post, I will briefly describe them and highlight the major differences. I will ask you a design question so we will discuss in the comment section below.

hsrp vrrp glbp

source: Orhan Ergun CCDE Study Guide – Workbook

HSRP and GLBP are the Cisco specific protocols but VRRP is an IETF standard. So if the business requirement states that more than one vendor will be used , then VRRP is the best choice to avoid any vendor interoperability issue.

For the default gateway functionality HSRP and VRRP uses one virtual IP corresponds one Virtual Mac address.

GLBP operates in a different way. Clients still use one virtual IP address but more than one virtual mac address is used. So each default gateway switch has its own virtual Mac address but same virtual IP address.

To illustrate this, lets look at the below picture.

 

hsrp virtual mac

source: Orhan Ergun CCDE Study Guide – Workbook

In the above picture, clients use same gateway mac address since the first hop redundancy protocol is HSRP.

If GLBP was in used, on the PC we would see different gateway Continue reading

Segment routing key points

Segment Routing  (SR) leverages the source paradigm. A node. steers a packet through an ordered list of instructions, called ‘ segment ‘.State is kept in the packet header, not on the router, with Segment Routing.

Resources such as the CPU and Memory are saved.

If you have 100 Edge Routers in your network and if you enable MPLS Traffic Edge to Edge, you would have 100×99/2 = 4950 LSP states on your Midpoint LSR. This is prevalent in many MPLS TE enabled network.

If you enable Segment Routing and if you evaluate the same midpoint case (since you assign a Prefix/Node SID for every Edge router), Midpoint LSR would have 110 entries instead of 4500 entries.

As for the scalability, everything is perfect. However, there is a caveat.

Segment list can easily get big if you use explicit routing for the purpose of OAM. If you do that, you may end up with 7-8 segments. In that case, it is pertinent that you check the hardware support.

Cisco claims that they have performed the tests on a number of service provider networks and that their findings show that two or three segments would be enough for the most explicit Continue reading

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