RE: Core Layer L2 or L3 [7:63708]
It depends if you are after theoritical advice, or practical advice. I have found it rare to have only L2 in the core (other than when using MPLS). The focus of the exam is that the core should add minimum latency to forwarding decisions, and thus the empahsis on why ACL's, VLAN aggregation etc, should all be done on the distribution / access layers, leaving the core to be very efficient. Not sure if this answers your question, but just my 2cents on what I have dealt with in the past! Cheers Troy Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63710t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Core Layer L2 or L3 [7:63708]
At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63714t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Core Layer L2 or L3 [7:63708]
At 11:44 AM + 2/25/03, Troy Leliard wrote: It depends if you are after theoritical advice, or practical advice. I have found it rare to have only L2 in the core (other than when using MPLS). The focus of the exam is that the core should add minimum latency to forwarding decisions, and thus the empahsis on why ACL's, VLAN aggregation etc, should all be done on the distribution / access layers, leaving the core to be very efficient. Not sure if this answers your question, but just my 2cents on what I have dealt with in the past! Cheers Troy Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? Again, remember core-distribution-access is only a model. There are perfectly valid implementations of this model that: -- have L2 WAN cores and no L3 -- have L3 WAN cores -- have L2 LAN cores and no L3 -- have L3 WAN cores As Troy says, it depends on why you are asking the question. Without further advice, I'd tend to agree with his practical advice. If it's exam-oriented, it depends on the exam. When I taught the CID course, it would never have been this restrictive in the actual class (i.e., the case studies would have more data). Whether some droid oversimplified the problem to an extreme as a test question, then the answer really depends on went on in the twisty little passages of their little minds. Howard Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63716t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Core Layer L2 or L3 [7:63708]
In a pratical world it all comes down to your needs for your business and the money you want to spend. We use a collapsed core with 2 4006 with Supervisor III's doing the layer 3 functions. We could add a high performance layer 2 switch for the core but it would be overkill. -Original Message- From: Peter van Oene [mailto:[EMAIL PROTECTED] Sent: Tuesday, February 25, 2003 8:13 AM To: [EMAIL PROTECTED] Subject: Re: Core Layer L2 or L3 [7:63708] At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63731t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Core Layer L2 or L3 [7:63708]
Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? It's best to always keep in mind where data jumps layers and then mentally follow your traffic through the network (to the extent possible - it's probably not that easy, but worth an attempt). I think a lot of Cisco study literature still holds to the L2 core concept, but ASICs have come a long way since the publication of much of those texts. An optimally configured L3 network will only be consulting the routing engine at the creation of flows and then the ASICs will do everything essentially at L2 afterwards. Having said that, it to a large extent can depend on how high up the product hierarchy you can afford to go. Lower-end stuff might still be faster with a true L2 box interconnecting L3 devices in some cases. So it helps to look at the capabilities of the specific products you have in mind and try to do a traffic analysis that takes into account how packets/frames will be routed/switched by that specific hardware set. Regards, Scott Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63744t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Core Layer L2 or L3 [7:63708]
At 04:08 PM 2/25/2003 +, [EMAIL PROTECTED] wrote: In a pratical world it all comes down to your needs for your business and the money you want to spend. We use a collapsed core with 2 4006 with Supervisor III's doing the layer 3 functions. We could add a high performance layer 2 switch for the core but it would be overkill. I don't disagree, however merely suggest that the model was driven by a vendor interested in selling more devices. Keep in mind you should also have a minimum of two devices per layer for resiliency ;-) If you have a high performance core that can provide access aggregation, packet processing and performance all at the same time, and your port costs are comparable per mbps, I'm not sure why you'd buy a distribution layer other than to help a rep hit his number for the quarter. -Original Message- From: Peter van Oene [mailto:[EMAIL PROTECTED] Sent: Tuesday, February 25, 2003 8:13 AM To: [EMAIL PROTECTED] Subject: Re: Core Layer L2 or L3 [7:63708] At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63782t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Core Layer L2 or L3 [7:63708]
Peter, The current rumour for the Academy CCNP program is that Cisco is dropping the 3 layer model and moving to a 2 layer model with L3 in the core for the BCMS course. I guess I'll find out for certain at Networkers in Orlando, Fla. this June. Prof. Tom Lisa, CCAI Community College of Southern Nevada Cisco ATC/Regional Networking Academy Cunctando restituit rem Peter van Oene wrote: At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63803t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Core Layer L2 or L3 [7:63708]
Interesting Since at cisco's SJ Corp campus we run a L3 core, a L3 dist, and a L2 access layer to the users. Larry Letterman Network Engineer Cisco Systems - Original Message - From: Tom Lisa To: Sent: Tuesday, February 25, 2003 3:17 PM Subject: Re: Core Layer L2 or L3 [7:63708] Peter, The current rumour for the Academy CCNP program is that Cisco is dropping the 3 layer model and moving to a 2 layer model with L3 in the core for the BCMS course. I guess I'll find out for certain at Networkers in Orlando, Fla. this June. Prof. Tom Lisa, CCAI Community College of Southern Nevada Cisco ATC/Regional Networking Academy Cunctando restituit rem Peter van Oene wrote: At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete [EMAIL PROTECTED] [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63812t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Core Layer L2 or L3 [7:63708]
At 11:17 PM + 2/25/03, Tom Lisa wrote: Peter, The current rumour for the Academy CCNP program is that Cisco is dropping the 3 layer model and moving to a 2 layer model with L3 in the core for At least in the provider space, L3 gets very nuanced between (G)MPLS and IP, the latter mostly for (G)MPLS path setup. The 3 layer model works pretty well for good-sized campus networks, but often is confusing for WANs. the BCMS course. I guess I'll find out for certain at Networkers in Orlando, Fla. this June. Adding to the absurdity of it all, and forgetting that one model doesn't fit all, Cisco and others have, for some time, used a four-layer model for service providers: Core:usually MPLS with a fast IGP for next hops Distribution:may have levels of internal hierarchy, but usually where most BGP happens -- either gateways to other ISPs or customer BGP Collector: Layer 1/2, but sometimes with IP-based MPLS/L2TP/etc tunneling, for broadband aggregation. Media gateways, DSLAMs, etc. Access: Equipment between ISP and customer, such as a BGP router run by a multihomed customer, a simple static/default router, broadband modems, etc. Peter van Oene wrote: At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63815t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Core Layer L2 or L3 [7:63708]
At 11:17 PM 2/25/2003 +, you wrote: Peter, The current rumour for the Academy CCNP program is that Cisco is dropping the 3 layer model and moving to a 2 layer model with L3 in the core for the BCMS course. I guess I'll find out for certain at Networkers in Orlando, Fla. this June. That would be very interesting. I am always leery of vendor models as they tend to have the vendor foremost in their mind :-) I always try and caution folks not too build hierarchy just to have it. Naturally, your 15 router OSPF network's visio diagram exudes a great deal more sharpness when it has a nice backbone and some number of non-backbone areas. However, in reality, many networks -large and small- are served far better with non hierarchical topologies. I am naturally digressing from the topic of three layer networks, but I think the message is the same. As others have pointed out, don't give in to the desire to build really neat networks that use a lot of technology unless you actually have a need for them. This to me would include building 3 layer networks where 2 layer ones would suffice (and be cheaper in both CAPEX and OPEX) Just my .02c as I sit here snowed-in in Arkansas of all places :-) Who would think I'd fly from Toronto to Littlerock and end up stuck in more snow than I left! Pete Prof. Tom Lisa, CCAI Community College of Southern Nevada Cisco ATC/Regional Networking Academy Cunctando restituit rem Peter van Oene wrote: At 11:05 AM 2/25/2003 +, Skarphedinsson Arni V. wrote: In a Core-Distribution-Access Layer design, would you keep the Core L2 or with high end L2/L3 switches such as the Cat6500 do you think it would be better to do L3 in the core ? I personally haven't found the need to have a Distribution layer in most networks. It's a model designed by vendors to sell boxes imho. Pete [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=63816t=63708 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
