The Long Road to Cisco
This is looking very bad for me at the moment. Two reviews without any filler content. I really need to start making some progress on notes and studies. I’m keeping this short and to the point. More time on studies this week. Last week was end of month and not really “productive” in the free time area with meeting targets and other junk. I did meet my target at 134%.
My POA is to spend more time on studie this week.
I’m sitting before work starts and thinking that maybe I should devote monday mornings to a “review session” of sort for the previous work week. This should provide me with a indicator where and what went wrong in my studies and where I need to change. It might also help me to identify where I am going wrong and what happened that lead to slow and “zero” progress. This may also help others to avoid some of the problems I am having.
Last week was my first week back into the books after changing jobs and I dare say professions, twice, in a short space of time. This was a delayed start because I forgot my study material at home the previous week. What I could have done to prevent this was probably made a note to pack the book when I got home or sign up to safari books (negating the use of a hardcopy boook altogether). In local currency the safari online option is just a little pricey to me but I will probably get there eventually when I hit the CCIE material.
The week itself was a disaster of note. I made good progress with the first post after revision of previous work done (catching up and revision) but the speed and pace slowed after that initial post when things began also picking up at work. I’m probably another couple of days away from making my next post barring hitches and problems coming up (work commitments, work, problems where I am staying and the need for sleep).
My evenings haven’t been going as planned with late night trips for food and staying late at work making work “after” activities almost useless because it would go in and straight out when I am that tired.
To try and work around all of the above, I am thinking I will physically plan study time when I know I don’t have something to do either early in the morning when I am still fresh and able to take in information or staying later after work when I can sit at a desk and do proper work.
My weekend didnt exactly happen as Saturday was booked for training with The Peer group. This messed up my weekend totally as I feel like I didnt complete anything useful this weekend other than do my chores and shopping on sunday and back to work today. (zero studying and reading happened).
I suppose life just sometimes happens and going with the flow is part of this process of achieving what I set out to do.
Lets see if this happens starting today.
When routers are connected to the same broadcast segment (I.O.W. several routers are in the same VLAN, on the same switch you getting the idea). One router is assigned the duty to maintain adjacencies with all other routers on the segment. This is the designated router (DR) and the DR router is selected using information in the Hello messages. For redundancy purposes a backup designated router (BDR) is also elected (There is a reason for this, read on).
DRs are created on multi-access links because the number of adjacencies grows at a quadratic rate. For a network of n routers, the number of adjacencies required would be:
Two (2) routers require the following adjacencies:
Four (4) routers require the following adjacencies:
Ten (10) Routers require the following adjacencies:
Maintaining a OSPF segment consumes more bandwidth and requires more processing resources (CPU and memory) as more routers are added onto a OSPF network (Due to keeping the tables updated and probability of changes occuring more frequently etc).
The DR and maintaining relationships
The purpose of a DR is to be the “one router” (sounds like the matrix) to which all other routers are adjacent (the router that has all the routes on the network). Using a DR reduces the number of adjacencies that consume bandwidth and processing to n – 1 (Larger networks will however still require more processing even if you are using a DR). With a DR the adjacencies scale more effectively and efficiently with the network (as one can see in the below figure and table).
To show this in a graphic way one can see how this “adjacency” relationship works without a DR, with a DR, and with a DR and BDR with a small example network using 5 routers.
Taking this a step further and plotting out the exponential growth requirements of OSPF adjacencies the table below shows the number of adjacencies needed for 1 – 10 routers (imagine the CPU and Memory requirements, not to mention the bandwidth consumption). Plan accordingly when implementing OSPF (at this point you generally use OSPF because you have a non-homogenous network environment and need the open standard because of this fact, I dont really see a point otherwise cause its such a resource hog and mission to setup).
The job of the DR
The role of the DR is to receive updates and distribute these updates to each segment router, making sure that each router acknowledges receipt and has a synchronized copy of the Link-State Database (LSDB).
Routers advertise changes to the “AllDRs” multicast address of 224.0.0.6 where the DR then advertise the Link-State advertisements (LSAs) using the “AllSPF” multicast address 224.0.0.5 where each router then ack receipt.
The BDR listens passively to this exchange and maintains a relationship with all the routers.
If the DR stops producing hellos, the BDR promotes itself and assumes the role of DR.
NB. DRs and BDRs are only useful on multi-access links because they reduce adjacencies. The concept of a DR is not used nor usefull on point-to-point links because there can only be one adjacency.
DRs are still however elected on Point-to-Point Ethernet links (most common type of links in networking these days) which is a rather pointless and resource waste/hog (as a DR is not really needed) which is why you will find that many design guides recommend changing Ethernet links to Point-to-Point mode to stop this from happening.
If a DR fails, the BDR is pomoted. The BDR is elected on the basis of highest OSPF priority, ties in OSPF priority are broken in favour of the highest IP ADDRESS.
The default priority is 1 and a priority of 0 (zero) prevents a router from being elected to the DR or BDR role.
Priority can be set from 0-255 (manually) to change the priority from default from the interface,
Router(config-if)#ip ospf priority number
DRs are inherently seen as stable entities once elected into the position, even if a Router joins a network with a “greater” priority the DR will not change.
To give an example of this an OSPF Segment with 5 Routers ( A – E, with different priorities 0 – 3). Taking what has been discussed previously A would be the DR, B the BDR, and E would never be elected. However this neglects the following set of circumstances:
Imagine the following sequence of events in this small segment,
In the above scenario the startup sequence of the routers caused the election of the DR and BDR (namely Router C is DR and Router B is BDR) which is not what would have been expected. This is because designated routers do not preempt, the elected DR/BDR serves in its role until reboot/failure (DR and BDR are stable entities on the network once elected).
In this network as it stands now If Router C restarts, Router B promotes itself to DR and Router A is elected BDR while C is down. If Router B goes down, Router A promotes itself and elects Router C or Router D (whichever has the highest IP Address). Finally when the BDR is rebooted, Router B wins the election for BDR.
NOTE: In addition to rebooting, clearing the OSPS process using the the command clear ip ospf process * on the DR will force the DR and BDR election.
Notes and Notices: This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.
Hello To anyone that still might visit my little webdom,
I’ve finally sorted out my new job, it’s been a roller coaster of note. This is not exactly what I had planned when starting out with this job in November with many things going totally up the creek and my stress levels going totally off the charts. The company I find myself in has nothing remotely to do with Cisco (which sucks) but with the market globally as it and the multitude of Cisco prospects streaming in at that time (read absolutely none) I was between a rock and a hard place with choices on advancing my career and personal development to get where I want to be in the future.
On a side note this makes me wonder whether the abundance of “Cisco” brain drain / skill shortage seminars / webinars / talks and press releases aren’t total BS and Cisco isn’t just trying to artificially stimulate their own ecosystem with the perception of a lack of skill (something to think about).
Short history, I started this job in November 2008 and I find myself now in a totally different department and job role as the one I started out in. This has a fair few positive and negative point, the main positive result is that I now have the time and energy to pick up my Cisco Books again and start posting updates and keep going with my Cisco studies, I really want to advance my Cisco Creds to the point where I want the with a CCIE or three in the furture (I’m a sucker for punishment).
I’m heading back “home” (I work and have lodgings in Johannesburg while I stay and all my stuff is in Pretoria) tomorrow and plan on packing my Cisco books to start the Long Road to Cisco again (note to self I really need to find a “place” in Johannesburg once I get my permanent contract).
Regards,
Deon
New posts might not happen for a while. I have changed jobs and the new job has nothing to do with Cisco. This leaves me with little time for studies. I have put too much time and effort into my Cisco studies to stop them now but the regularity of updates and the pace of work will not be like it was before.
OSPF develops neighbour relationships with routers on the same link by exchanging hello messages (a.k.a hellos).
At the initial exchange of hellos, the routers add each other to their respective Neighbour Tables (The Neighbour Table in this case acting as a list of connected OSFP enabled routers).
OSPF Enabled Routers send multicast hellos with a destination address 224.0.0.5 on all OSPF-enabled interfaces.
OSPF sends out hellos every 10 seconds on a broadcast link (a link with more than 2 nodes on the same segment like Ethernet) and 30 seconds on a non-broadcast (a link with only 2 nodes on the same segment; exceptions *shrug* exist for NBMA) link.
The Hello message contains:
After the initial hello exchange between two routers, an exchange of network information begins. After routers have synchronized their information they are adjacent.
Routers must go though various states from the initial relationship “hello” that transitions through a process before forming a “full” adjacency as shown above in the picture.
Once a full adjacency is achieved, tables between routers must be kept updated to prevent loops and routing errors. LSAs are re-sent when a change occurs, or every 30 minutes to keep routing information “fresh”.
Going through the different “states” a neighbour relationship can be in:
Hellos between routers continue to be sent periodically and the adjacency is maintained as long as hellos are exchanged. Missing hello messages result in a router declaring the adjacency being declared dead.
As soon as OSPF identifies a problem, it modifies its LSAs accordingly and sends the updated LSAs to the remaining neighbours (with full adjacencies).
Being event-driven, this LSA process intrinsically improves convergence time and reduces the amount of information that needs to be sent across the network.
A key piece of information exchange in LSAs is the OSPF metric information. Many OSPF vendors assign each link a cost of 10, Cisco makes cost inversely proportional to a 100 Mbs
An Admin can override the default cost. This would be done for compatibility reasons (with other OSPF speakers or because the link is more than 100 Mbps).
Sometimes the meric is equivalent for multiple paths to a destination. In this case, OSPF will load balance over each of the equivalent interfaces. Cisco routers will automatically perform equal-cost load balancing for up to four paths, but this parameter can be increased by configuration to as many as sixteen paths.
The cost is applied to the outgoing interface. The routing process will select the lowest cumulative cost to a remote network.
Notes and Notices:
This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.
Cisco Live! is the Cisco annual ‘Networkers’ conference. For the first time ever the will be held in Sandton, Johannesburg on 1st – 4th December 2008. Cisco Live! will be the place for network engineers from all over Africa gather for technical training, education and networking. For the past eleven years, the conference has been at the forefront of educating delegates on new technologies.
The Cisco Live! conference will incorporate a new concept ‘Networkers at Cisco Live!’ with a mix of technical and business offerings. This format broadens traditional technical focused meet-ups to include executive tracks that examine the role of technology in driving business value in a challenging economic climate. The theme of this year’s conference is ‘The Power of Collaboration’ and delegates can look forward to thought-provoking keynotes from local and international Cisco executives and industry experts.
Networkers at Cisco Live! will be held at the Sandton Convention Centre and will attract more than 1,500 delegates, making it the largest Networkers conference in South Africa to date. The program will comprise various sessions, ranging from technical trainings to an invitation-only executive symposium. Delegates will also have the opportunity to view the World of Solutions demonstration area, which will showcase collaboration and communication tools and technology, such as TelePresence.
A Word from Steve Midgley the Managing Director of Cisco South Africa
“South Africa is the first country outside the United States to introduce the Cisco Live! brand. With Cisco Live!, we are taking the event to the next level to provide a platform where industry players can learn new technologies, discuss business trends, share ideas and network,” said Steve Midgley, Managing Director, Cisco Systems South Africa.“In recent years, specialization, globalization and new technologies have resulted in more collaborative environments made up of global, virtual networks and communities that improvise and find more productive, innovative and faster ways to do business. Cisco puts communications and collaboration capabilities within the context of a business process to allow workers increase their productivity, speed and agility,” added Midgley.
Speakers
Rick Hutley, vice president of Global Innovations for Cisco Internet Business Solutions Group, will be a keynote speaker at the event. Hutley, responsible for engaging Cisco’s largest global customers, will discuss the role of collaborative technologies in addressing the key business challenges and opportunities faced by organisations today.
Also speaking at the conference will be World Wide Worx’s Arthur Goldstuck, who will present findings from the Cisco-sponsored Internet Access in South Africa 2008 research report. Goldstuck’s presentation will cover the latest trends in Internet access and will set the scene for a discussion around the future of connectivity in South Africa, which plays a crucial role in collaboration.
For more information on Networkers at Cisco Live! www.networkersafrica.co.za
Open Shortest Path First (OSPF) is an open standard routing protocol, defined in detail in many Internet Engineering Task Force (IETF) Request For Comments (RFCs)Â including RFC 2328.
OSPF uses the Shortest Path First (SPF) Algorithm to calculate the best path to a given destination. OSPF builds loop-free paths that converge quickly, but often requires more processor power and memory than distance vector routing protocols (EIGRP).
OSPF can be more complicated because there are many topology and configuration options to consider versus EIGRP that has is has less of a learning curve.
OSPF is designed to offer flexibility in network design (OSPF is an open standard vs EIGRP that is Cisco Proprietary) which IOW allows OSPF to supports linking between different vendors Cisco, HP, etc.
OSPF Basics
OSPF as mentioned before is a Link-State routing protocol (basics) that is based on the Dijkstra Shortest Path First (SPF) Algorithm.
When one compares distance-vector routing to link-state routing;
OSPF is used within an Autonomous-System (AS). It has advantages over distance-vector routing protocols:
When a link goes up or down in a link-state routing protocol network, a link-state advertisement (LSA) is generated. LSAs are shared with neighbours and a topological database (a.k.a link-state database (LSDB) or Topology Table) is built.
LSAs are marked with sequence numbers so that older and/or newer versions of advertisements can be recognized (start 0×8000 0001 end 0xFFFF FFFF before rolling to the start again). The eventual goal is that all routers in the same AS has the same LSDB which is then processed using SPF from which the best routes are selected and a routing table created.
The Topology Database (LSDB) is the routers view of the network within the AS it operates. This includes every OSPF router within that area and all connected networks.
To view the current status of the link state database,
Router#show ip ospf database
The Topology Database is updated by LSAs and each router in a AS has exactly the same topology database. All routers must have the same view of the network otherwise routing loops or loss of connectivity will occur.
When a router realizes there has been a change to the network topology, the router is responsible for informing the rest of the routers in the area with a LSA. This happens mostly due to:
In any of the above cases, the router will generate an LSA and flood it to all neighbours with the following stipulations:
All OSPF operations centre around populating and maintaining
Notes and Notices:
This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.
So finally South Africa is treated to the bright, amazing, and wondrous release of the Applie iPhone 3G (totally missing out on Version 1), that’s unless you had a cousin, connection or friend in another “more developed” country smuggle one in for you. I would have been there on the launch day (I like the vibe of launch days) but I was quad biking in the bushveld (sun, wild animals, 4×4 lots of fun and first holiday in a long time).
Here is the laugh though; since the launch (a week ago today) I have seen 1 (total) being used (at a Fortinet mixer last night). I have decided against being a South African first adopter becuase of articels like this and this and don’t want to be find out first hand how bad Vodacom support can be on a new product.
I stopped into a Voda-store (local reseller) to have a listen to the whole story on a “Apple package deal” and was thoroughly disgusted as they wanted me to sign “another contract” on top of the one I already have. I had to ask three times specifically NO CONTRACT ONLY HANDSET before I was told that the Voda-super-store was the only place that sold iPhone out-of-hand for the super price of ZAR 7,569. These sharks don’t tell you when you ask, or listen when you ask and con people into signing contracts for 24 months onto existing 24 month contracts. Totally Disgusting this being one of their resellers and how they operate. Probably why Vodacom South Africa has a Net Profit of ZAR 8 Bn and Earnings before interest, taxation, depreciation, amortisation, impairment, profit/loss on disposal of property, plant and equipment, investment properties, intangible assets and investments of ZAR 16.5 Bn.
Today on MyBroadband they had a nice piece on the cost of the iPhone in other markets versus here.
Anyone want that iPhone 3G with added Apple Tax all things considered? Seems a little much for me taking into consideration what it says on the box isn’t what the product seems to be doing all over the world.
So while I am working diligently at getting back into the Cisco swing of things with my study notes and Cisco Press books and making posts on a regular basis (this is happening just slowly OSPF is beating me up left, right and centre). This all after some added work commitments and other stuff has been sorted out.
This came in a Cisco email today and I really enjoyed it. Good for a laugh or two. These cubicle jockeys are somewhat athletic compared to the ones I know.