Is the Distribution Layer Still Needed? 72
arnie_apesacrappin wonders: "I'm in the process of designing the network for a new building in what I would consider a small to medium sized company. It is on the scale of tens of access layer switches, not hundreds. There is a ongoing argument about the need for a distribution layer. My position is that with today's layer 2/3 switches in the core, the distribution layer is outdated for a network of this size. The layer 2/3 core can provide all the aggregation services of the old distribution layer and the routing/filtering functionality of the core with better price and performance. My opponents can only argue that having a distribution layer is the standard. So, are there good reasons for having a distribution layer in a small to medium network? If you were going to argue against the distribution layer, what points would you make?"
Glad you don't work here. (Score:2, Insightful)
Quit trying to be clever. Proper use of L3 equipment around the LAN and judicious use of VLANs is smart. Current equipment will let you design in redundencies for failed hardware so trying to aggregate all your networking smarts to a central point of failure is not cool. Frankly it sounds like you're trying to impress management without thinking of the ramifications.
Re:Glad you don't work here. (Score:2, Funny)
What? (Score:4, Funny)
Re:What? (Score:2, Funny)
It can be done. (Score:4, Interesting)
Basically, if you eliminate distribution, you have to have a lot more processing power and lots more ports in the core. Depending on the network's size and distribution it will probably be more costly to build such a robust core. Also, don't forget that this thing is certain to grow. Can it scale easily and cost effectively with the more robust core? There will come a point that it will not scale effectively and the distribution layer will have to be introduced.
Re:It can be done. (Score:5, Insightful)
Re:It can be done. (Score:1, Insightful)
Re:It can be done. (Score:1, Insightful)
Spoken like a true CCNA (Score:5, Insightful)
Those three "layers" are abstractions, nothing more. The "distribution" layer is simply a term for traffic shaping and optimization. It's very useful in eliminating excess resource use on beleagured routers. Eliminating the layer is nothing more than simplifying your backbone architecture. There is no "layer" to eliminate except the theoretical one.
It always amazes me how Cisco-certified (not making any acusations here) network techs speak an entirely different language from university-educated ones. They talk about Cisco-specific concepts like they're set in stone universally, and use Cisco jargon for common and/or basic concepts.
There are other options besides Cisco, and not every network fits within the nomenclature of Cisco Jargon. You'd do yourself an immense favour to lean more about generic architecture concepts.
I don't want to sound mean, but a Cisco cert is about as useful as an MSCE.
Re:Spoken like a true CCNA (Score:1)
Re:Spoken like a true CCNA (Score:1)
and its not a matter of who i voted for, i just think moore is a putz
Re:Spoken like a true CCNA (Score:3, Insightful)
To the CCIE's defense, he gave a balanced and reasoned opinion that was not rife with Cisco jargon.
I, on the other had, find it interesting to talk to university educated CS majors (I graduated with a BA in Math, but have worked as an SA and programmer for 17 years) who use lingo (especially pattern nomenclature) and discuss concepts (stateless session beans, oooooooooh) o
Re:Spoken like a true CCNA (Score:3, Interesting)
When I applied for a job at the same University as Network-something-or-another y
Re:Spoken like a true CCNA (Score:1)
Re:Spoken like a true CCNA (Score:2, Interesting)
I love the irony you bring to light about university settings.
One would think those working for and under university level expectations, and job applications requiring EVERY-SINGLE-JOB-YOU-EVER-HAD to be listed with it, to be somewhat on the ball about how to do things, at least efficiently.
But, no.
What is often forgotten is that universities are rarely anything less than a bureaucracies. Therefore you, as I and my classmates, might get a "Unix Administrator" who is unaware of the web interface t
Re:Spoken like a true CCNA (Score:3, Informative)
Reading TFA and the other posts, I can see the point of reaching for that degree of networking control in a big enterprise. At the other end of the scale - the home LAN level, network bandwidth is practically where nuclear-generated electricity once promised to be - too cheap to measure. I went from 10Mb to 100Mb because it was cheap and available, not because of need, and any future migrations will likely be the same.
You're ob
Re:Spoken like a true CCNA (Score:3, Funny)
Re:Spoken like a true CCNA (Score:2, Insightful)
Absurd! (Score:3, Funny)
Re:Absurd! (Score:1)
Re:Absurd! (Score:1)
Re:Spoken like a true CCNA (Score:2)
Thank [insert-diety-here] someone cleared this up for me. I thought I was well-versed in networking, but this article left me wondering what classes or books I missed. Now the answer is clear - Cisco. I make it a point to never attach myself to a brand-centric technology or concept.
Again, thank you.
You don't need it (Score:4, Informative)
You are correct that the layer 3 switches offer a different perspective on how networks can be drawn today.
It used to be that big switches would sit in the computer room, with clunky slow routers sitting on top of them, acting as Routers-On-a-Stick, with some sort of trunk connecting them to the core switch.
I think the easiest design that will give you the most benefit would be to just trunk a link to whatever closet, and use a cheap layer 3 switch (perhaps Extreme or a similar variety) in the data closet, for end user hookups.
Have gateways set up on the switch, use a default route pointing back to the core, and divide up the ports to whatever VLANs you ported over--I prefer to have a management VLAN and a few ports set up for that, maybe an extra one for SPAN/Mirroring if necessary.
The end user traffic would likely never be routed until it reached the core, unless you'd like to trunk the core traffic over to the closet. Then the access layer switch could route to the core subnet if necessary and save the core switch(es) the effort of doing such routing. If you have a small business, it wouldn't make much difference either way--many chassis based layer 3 switches do 64Gb per second routing with their fabric, and it is unlikely anyone would notice a delay from the routing in the closet or in the core.
Again, it depends on how you want it to look and how you want trouble shooting to be. But you are absolutely correct--a distribution layer is no longer necessary. I would consider it, really, to be the Core/Distribution and then Access Layers, or the Core and Distribution/Access Layers.
You still are using the concept of the distribution layer, but it has merged with another layer, depending on your design.
Oh, and don't forget about spanning tree
No clear choice. (Score:3, Informative)
KISS (Score:1)
It basically comes down to switching at the core and routing at the edge. No need for all the jargon.
Re:KISS (Score:2)
Enterprises have problems where developers need to operate in the same offices as finance or sales. The needs of the groups are very different (e.g. developers need simulated development environments which won't take out accounting, accounting needs very limited and controlled access to very special systems... ) and any one of the employees may be operating off-site through a VPN or shifting sites daily.
Moving the employees around the network hardware isn't acceptable anymore. The network needs to be fl
Depends on the size of the network (Score:2)
Speaking from the $$$ side, it looks like you have priced out both options and the core-only network would be cheaper. In that case, more po
Layer 3 Switch? (Score:2, Interesting)
Re:Layer 3 Switch? (Score:4, Informative)
Re:Layer 3 Switch? (Score:1)
Re:Layer 3 Switch? (Score:1, Insightful)
You were taught incorrectly, or, perhaps a more plausible possibility is that you learned incorrectly. Ethernet hubs and switches are both Layer 2 devices. Your best bet is to read
Re:Layer 3 Switch? (Score:2)
I fully agree though that when dealing with hubs that are for instance 10/100BT then they are forced to concider how to slot in each request between backplanes. The 10 devices work as a single hub, and the 100 devices work as another hub. There is also switching logic which bridges the two together. Usually the up
Re:Layer 3 Switch? (Score:2)
Re:Layer 3 Switch? (Score:2)
The operate at the speed of the slowest connected device.
So, let's say ( for some bizzare reason ) you have a 10/100/1000 multi-speed hub.
If you plug a 10mb device in, all ports run at 10mb.
Since it's rebroadcast across all channels, there is no way to do "buffering" of a 10mb port usually.... which is what a multi-speed switch will "usually" do.
buffer, or slow connections across any set of ports talking slower.
Re:Layer 3 Switch? (Score:1)
Sheesh.
Re:Layer 3 Switch? (Score:1)
Read mine; that's all the proof you'll need.
Re:Layer 3 Switch? (Score:3, Informative)
Switches have grown up, since the advent of VLAN's, they've been able to 'route' between vlans, and have expanded to OSPF, and other high end routing protocols, while keeping the port count. These higher end switches don't usually have WAN ports (T1, T3 type), or the ability
Re:Layer 3 Switch? (Score:1)
I have never found a need to set that on my switch, and every place I have even been that uses them all it does is get in the way of proper installation of HACMP clusters.
Re:Layer 3 Switch? (Score:2)
If you are utilizing chassie level switches, you'll run into them. The point is to have different IP subnets on the same 'switch', and have the switch route appropriately (or not as needed by the network design... without the routing piece, a host on VLAN 1, can't see a host on VLAN 2. That might be how you want it.)
If you have a chassie with 8 blades of 48 ports each, it's unlikely that you want all of them to be on the same subnet, so you have VLAN's.
Re:Layer 3 Switch? (Score:2)
The advantages of multiple physical networks without the disadvantage of having to physically install multiple physical networks.
Note that if you're not in an environment where multiple physical networks would not be an advantage (or even a consideration) VLANs are probably not of interest to you.
Re:Layer 3 Switch? (Score:2)
That is a bridge on layer 2 (Score:2)
You were taught wrong. A bridge is a device that routes on layer 2.
A switch is a device that does the operations in hardware as opposed to software. Generally a switch will run on layer 2 because it is much easier to put the layer 2 protocols in hardware, but sometimes they will work in layer 3. (actually most layer 3 switches are a combonation, doing the common tasks in hardware, but things less common in slower software)
Unless specified otherwise, most switches today operate on layer 2, so nobody use
Re:That is a bridge on layer 2 (Score:2)
I should mention that most layer-2 switches to not have the spanning tree stuff that bridges have, so they are not the same thing. A switch is a smart hub, in that it doesn't send traffic to everyone, but it isn't smart enough to find loops in the network and deal with them. Now that networks run only routeable IP this isn't a big deal. Back when the transition from bridges to switches was made, was the tail end of the time when your network was likely to run some protocol that wasn't router friendly,
Re:That is a bridge on layer 2 (Score:2)
"Route" is a special term which applies only to layer 3 protocols.
Software/hardware doesn't matter.
A bridge was an older peice of hardware designed to connect two broadcast domains, useful for nasty protocols like NetBEUI.
A switch was a multiport bridge. the MAC tables in modern switches are quite capable of bridging. I've been told that older switches had very limited MAC tables so the distinction between a bridge with two ports and a huge MAC table v.s. a switch with a huge number of ports and a s
It's usually not needed in a network of that size (Score:5, Informative)
1. how you link your merged core/distribution switches: if your access uplinks are layer 2, you then have to span VLAN across core/distribution switches. If you plan on having your access switches perform layer 3 routing look into the costs your vendor may charge for that functionality. Some charge as much as $10,000 for the license.
2. Be careful you grow your VLANs and spanning trees. Definitely use per-VLAN spanning trees. Also seriously consider rapid spanning tree or vendor specific hacks (uplinkfast, backbone fast, etc.)
3. Use server access switches. Seriously consider redundant control processors in these.
4. Seriously consider redundant control and switch fabrics for the the core/distribution switches. In the three-layer model, this was not as much of a requirement. Also seriously consider the failover time associated with the redundancy you bought. Times ranges from stateful/1 second failover to 90 second reboots to the redundant processor.
5. If you do layer 3 routing and the access layer be very careful with your routing protocol design and avoid black-holes. Run through all failure scenarios and make sure you're covered.
6. Consider where you want to perform filtering for security, QoS, etc. By eliminating the distribution layer, you're forcing this the access layer. (arguably it belongs there, but think about how many places you'll be configuring and monitoring)
7. Most importantly, consider the costs after you've considered the above. You may find out that you're not saving much. Most of my clients do save, but some find out that after they've added redundancy and possibly upgraded switch models they are close the same cost.
8. Consider your support group. What are they used to? Can they adapt? Can they handle the added functionality that's been pushed to the core or access switches.
Again, I have clients with 1500 nodes running fine with a combined core/distribution. I also have a clients with 200 nodes that mandated three layers. IMHO the break point is somewhere around 1000-1500. As always every place is different, be careful, plan and you'll be fine.
Re:It's usually not needed in a network of that si (Score:3, Informative)
Buying 15 smaller switches, and collapsing/trunking 200 switches onto 15/30 Gig/10Gig uplinks to a core means my core only needs 15/30 ports, instead of 200+. Sure, you don't *need* it, if you can afford the port density of that size on your core, but any decent sized network is going to be pressed for that kind of cash
It's significantly cheaper/easier to provided redundancy for 30 GigE ports than it is to provide redundancy
Think in terms of scalability (Score:2)
Alot of vendor supplied designs are made assuming that you are going to grow exponentially... which may or may not be your case.
Depends on how you define "distribution layer" (Score:5, Interesting)
We normally have one port on the switches for each system, with the exception that in some locations we have smaller switches to allow them to share a line, so that we don't have to rewire the building. We also use some smaller switches as repeaters to parts of the building too far away to connect directly to the central switches. Those small switches outside of the server room, along with all our servers and systems, might be considered our access layer.
Then we have a tiny linksys router, intended for home use, connecting the entire building to the internet. I know, it sounds scary, and unprofessional, but it seems plenty capable of filling the bandwidth of a T1 and tracking as many simultaneous tcp connections as we use. We'll consider replacing it at the first sign of trouble. I guess this is our core layer.
I suppose that whatever you use at the top level to connect your systems to create a single network can be called your distribution layer. The switches may get cheaper over the years, but it's the same thing. If you just have a chain of 8 port switches running around the building, then your distribution layer is a bunch of 8 port switches.
However you design your distribution and access layers, your main goals should probably be to minimize line problems (mostly due to distance) and avoid bottlenecks. You seem concerned about price, so if you decide to use 100mbit switches to keep the price down, I recommend that get the kind that have gigabit uplinks and plug them into a gigabit switch, and plug your servers into the gigabit switch as well. Otherwise, your effective bandwidth will be 100mbit total rather than 100mbit per user.
I've designed just such a thing (Score:5, Informative)
I'm a consultant and work with hardware from just about anyone, so it makes no difference who they bought. We were hired to design a network for this school using various vendors equipment. Primarily to compare costs.
In the end, they went with a solution from HP. A single 5300xl in each building connected to a bunch of 48 port edge switches in each closet. Their server room has a 5300xl with a couple Gig blades and a second 48 port Gigbit switch.
What really decided the issue was cost. They didn't need support for all the assorted protocols and features you get with cisco, and they didn't want to pay for it. With cisco, you had a 6500 series monster in the datacenter, then a distribution switch in each building, and a bunch of edge switches.
The HP solution was well under a third of the cost of the cisco solution, also free lifetime next day replacement warranty on hardware. For the money they saved, they can afford to have a shelf full of spares, including a spare core switch.
Personally, instead of looking at what model you want to use, look at what you need your network to do, then talk to your prefered vendors and see who can do it at the best price point.
No its still needed (Score:2)
Aside from the benefit of building the physical layout to represent (as much as possible) the hierarchical virtual topography in aiding troubleshooting, the Cisco Campus/DS layered design allows for the layering of services without having to swap out switches e.g. bringing routing to the switch port isn't g
Re:No its still needed (Score:2)
Your budget is too big (Score:2, Insightful)
For sending email and word docs around, you really don't need the whole Cisco hierarchy. On the other hand, If you're sending uncompressed production video around, it's not enough.
Your network is too small. (Score:2)
If you have such a network, please post pictures. The Slashdot populace would LOVE to see that beast. Shudder
Re:Your network is too small. (Score:1)
But I know a network consult who has described to me far worse scenarios:
- Unstable networks that don't behave the same if the various elements are powered up in a different order
- People bringing in their own wifi equipment and creating and routing new subnets on their own initiative, and the network admin people don't see it for a couple of MONTHS
- Cheapo hubs that assume all equipment is at least FDX 10
Re:Your network is too small. (Score:3, Interesting)
And that, in a nutshell(tm), is what I absolutely hate about the "high end" stuff. The fact that the up-front cost to gain ownership of the physical device is one thing, but the hefty recurring fees to get ANY kind of support (including, as far as I can tell, bug-fixes, security updates, and so forth) get insane very quickly. Especially when you're presumably willing to pay the
Re:Your network is too small. (Score:2, Informative)
Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC conta
Re:Your network is too small. (Score:2)
Distribution layer exists only in the Ciscoland (Score:3, Insightful)
The term "distribution layer" is defined by Cisco, which is just a corporation. There is no standard where you will encounter this term.
The most well-known networking standards are the OSI model [webopedia.com] and the TCP/IP model [networkdictionary.com]. Neither of these standard models include the term "distribution layer", which means nothing by itself: Is it about physical-electrical distribution, data distribution or information distribution?
I personally dislike "standards" or tech-speak set by corporations and I believe international bodies and computer scientists should be preferred when it comes to standards and technical jargon: Imagine two computer scientists, one using Cisco-speak and the other knowing only Microsoft-speak, how are they going to communicate? It's impossible! - unless they both adopt a common language like these proposed in the OSI or TCP/IP model.
I personally can communicate network concepts using the OSI model, and I am completely unaware of Cisco-speak. In an attempt to answer your question, I will assume that by "distribution" Cisco means "routing", which translates to "Internet layer" in TCP/IP-speak and is related to the Internet Protocol, while in ISO-speak it translates to "Network layer". If my understanding is correct, then the answer is that no matter how small your network is, you will want to use routing, for example for connecting your small network to the Internet. Even if the routing functionality is included in a device of another layer, or even when it is implemented in software, it will always be there, no matter whether the users or even the administrator can see it, especially if you are going to use the TCP/IP protocol suite.
Re:Distribution layer exists only in the Ciscoland (Score:2)
Re:Distribution layer exists only in the Ciscoland (Score:1)
The OSI and TCP/IP models are not even remotely analagous to the Cisco model of Core / Distribution / Access. OSI and TCP are describing network stacks, the Cisco model is describing a suggested physical network topology. Since your assumptions are unbelievably false, and you haven't bothered to do even the most cursory amount of research, the rest of your bits are wasted. Way to go.
--
lds
ex CCNA wannabe (Score:1)
I studied for the A+... then the changed the test and I didn't bother.
I read a few MCSE books... got bad vibes.
I took a CCNA course (semesters 1 2 and 3), picked up every last vender-neutral concept I could. Then the thing started selling Cisco specific concepts, moving away from concept and towards (cisco specific) implementation, teaching you to hawk cisco gear as much as know the (cisco-bent) basics.
I quit.
G
Re:ex CCNA wannabe (Score:1)
1- As for whether distribution layer is needed or not, I aggreed with an earlier post (somewhere up the page) that this is just an abstraction. By "distribution layer" you mean the place where filtering and access control (i.e. policy networking) is happening. So IMO it all depends on whether or not such functionality is required in your company.
2- I've seen a few posts bahsing cisco concepts and certs in this article. Personally I have been through a few
Real world story. (Score:2)
We ended up using a distribution layer because it made the config easier, and centralized a lot of complexity, and didn't cost an arm and a leg in fiber uplink ports. We utilized Extreme Networks 7i switches as distribution (44 gig fiber links), which (compared to core chassie blades for the same fiber density) were cheep. We then uplinked each distribution layer switch (2 of them) to the 4 core chassies. This cost 8