Re: Number of routes and memory usage [7:70299]
At 1:08 AM + 6/9/03, The Road Goes Ever On wrote: or to put it another way, why bother when memory and CPU is relatively cheap ( you DO use 3rd party memory, don't you ;- ) As I tell all my customers, it doesn't hurt to max out the memory. Never can tell when you will need it. ( and it helps me retire quota ) As I say when I want to yank Priscilla's chain, design is dead. This kind of work is irrelevant. Ah, but what is design? Seriously, in all but the very largest enterprises, your advice is quite reasonable. It wasn't always the case that adding 500 or 1000 routes was insignificant, especially when the 7000's silicon switching cache held only 500 or 1000 routes. Right there, however, is an issue I'd call operational design or implementation engineering. The issue, even then, wasn't RAM usage, but cache thrashing. And so it is, even today, with small enterprise routers, or with large carrier routers. Raw memory size is rarely the problem, but route processing can be. For OSPF, an approximation of the load to do a Dijkstra computation is: (routes * routes) * log(routers) of course, the Dijkstra is only part of the route computation, dealing with intra-area routes only. The total computation then grows linearily with the number of inter-area and external routes that the area must consider. Even more basic is how often this computation has to be repeated, which comes back to the question of route stability. The Dijkstra algorithm itself is 40-some years old, and faster variants are available. There's no way we can get into subsecond convergence with an unmodified Dijkstra and alternatives to hellos. In the absence of additional processing that uses the same processor [1], the limiting factors tend to be less the absolute number of routes than the rate of route change and the level of interconnection among routers (hierarchy decreases that). A major issue in the global Internet is less the load on specific routers, than it is the overall slowing of convergence and a greater tendency to blackholing. Now, when you get not into network design but protocol design, some of these factors that you could ignore re-raise their heads and bite you. In a large ISP router, memory speed is a major limitation. As a designer, you may indeed be limited by the cost of SRAM vs. DRAM, or whatever is the fastest available memory. You will also be limited by the forwarding fabric -- shared bus, as in the 7500, tops out at around 2 Gbps with shared memory being somewhat but not overwhelmingly more capable. Crossbar fabrics then become the basic usable technology, but they have their own problems of a limited number of points of connection. [1] Knowing what other processing goes through the route processor is important and also release- and platform-dependent. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70402t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Number of routes and memory usage [7:70299]
Curious wrote: Hello again friends, I want to thank Mr Jvd for his help, and I would like to post again my question, It is very surprising that we all have been working with routers for years but there is no answer for this question, I can evaluate the ammount of memory used in my router for every type of route, but I would like to learn from someone more skilled than me and test my results :) :) The reason you're not getting an answer isn't because we're blowing you off. It's because it's too complicated for an easy answer. You'd have to talk to the IOS developers for a good answer. I have a training manual that was used to teach new IOS developers. I checked it. Although it talks a lot about memory management, it doesn't mention how much memory each route takes. For one thing, it would certainly depend on the routing protocol. EIGRP's scaled, composite metric takes more bytes than RIP's hop count, for example, although from what I learned about memory management from the developer training, memory is managed in chunks, so a few bytes probably wouldn't matter. Most of the routing protocols save more info than just the routing table. OSPF and EIGRP have a topology database, for example. So that would definitley affect memory usage. Also, unless you plan to save all of the Internet BGP routing table, it's simply not an issue. Routers have enough memory to store routing tables in most cases... So, it's not a very relevant operational questions?? If it's a research project, well get researching. Asking us won't help, I'm afraid. :-) Priscilla Hello folks, I have to evaluate the impact of adding almost 1000 routes in my network, and what I want to know is simple: How many memory do I need for every new router? Do you know a simle rule? What I want to know is the relationship between the number of routes and the memory consumption. I can evaluate know this by looking how many routes are in may routing table and the memory used, but I would appreciate any experience from you. Thanks group! Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70353t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Number of routes and memory usage [7:70299]
Priscilla Oppenheimer wrote in message news:[EMAIL PROTECTED] Curious wrote: Hello again friends, I want to thank Mr Jvd for his help, and I would like to post again my question, It is very surprising that we all have been working with routers for years but there is no answer for this question, I can evaluate the ammount of memory used in my router for every type of route, but I would like to learn from someone more skilled than me and test my results :) :) The reason you're not getting an answer isn't because we're blowing you off. It's because it's too complicated for an easy answer. You'd have to talk to the IOS developers for a good answer. I have a training manual that was used to teach new IOS developers. I checked it. Although it talks a lot about memory management, it doesn't mention how much memory each route takes. For one thing, it would certainly depend on the routing protocol. EIGRP's scaled, composite metric takes more bytes than RIP's hop count, for example, although from what I learned about memory management from the developer training, memory is managed in chunks, so a few bytes probably wouldn't matter. Most of the routing protocols save more info than just the routing table. OSPF and EIGRP have a topology database, for example. So that would definitley affect memory usage. Also, unless you plan to save all of the Internet BGP routing table, it's simply not an issue. Routers have enough memory to store routing tables in most cases... So, it's not a very relevant operational questions?? If it's a research project, well get researching. Asking us won't help, I'm afraid. :-) or to put it another way, why bother when memory and CPU is relatively cheap ( you DO use 3rd party memory, don't you ;- ) As I tell all my customers, it doesn't hurt to max out the memory. Never can tell when you will need it. ( and it helps me retire quota ) As I say when I want to yank Priscilla's chain, design is dead. This kind of work is irrelevant. Reminds me of a question I saw on a practice test somewhere - which router would you use if money were no object? Believe it or not, the correct answer was not the most expensive one. :- Priscilla Hello folks, I have to evaluate the impact of adding almost 1000 routes in my network, and what I want to know is simple: How many memory do I need for every new router? Do you know a simle rule? What I want to know is the relationship between the number of routes and the memory consumption. I can evaluate know this by looking how many routes are in may routing table and the memory used, but I would appreciate any experience from you. Thanks group! Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70372t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Number of routes and memory usage [7:70299]
Hello again friends, I want to thank Mr Jvd for his help, and I would like to post again my question, It is very surprising that we all have been working with routers for years but there is no answer for this question, I can evaluate the ammount of memory used in my router for every type of route, but I would like to learn from someone more skilled than me and test my results :) :) Hello folks, I have to evaluate the impact of adding almost 1000 routes in my network, and what I want to know is simple: How many memory do I need for every new router? Do you know a simle rule? What I want to know is the relationship between the number of routes and the memory consumption. I can evaluate know this by looking how many routes are in may routing table and the memory used, but I would appreciate any experience from you. Thanks group! Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70299t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Number of routes and memory usage [7:70299]
sounds like the perfect topic for a PhD research project. Assuming, of course, that number of routes is the only variable which effects sizing of memory Curious wrote in message news:[EMAIL PROTECTED] Hello again friends, I want to thank Mr Jvd for his help, and I would like to post again my question, It is very surprising that we all have been working with routers for years but there is no answer for this question, I can evaluate the ammount of memory used in my router for every type of route, but I would like to learn from someone more skilled than me and test my results :) :) Hello folks, I have to evaluate the impact of adding almost 1000 routes in my network, and what I want to know is simple: How many memory do I need for every new router? Do you know a simle rule? What I want to know is the relationship between the number of routes and the memory consumption. I can evaluate know this by looking how many routes are in may routing table and the memory used, but I would appreciate any experience from you. Thanks group! Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70305t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Number of routes and memory usage [7:70299]
At 3:48 PM + 6/7/03, The Road Goes Ever On wrote: sounds like the perfect topic for a PhD research project. Assuming, of course, that number of routes is the only variable which effects sizing of memory Curious wrote in message news:[EMAIL PROTECTED] Hello again friends, I want to thank Mr Jvd for his help, and I would like to post again my question, It is very surprising that we all have been working with routers for years but there is no answer for this question, I can evaluate the ammount of memory used in my router for every type of route, but I would like to learn from someone more skilled than me and test my results :) :) Hello folks, I have to evaluate the impact of adding almost 1000 routes in my network, and what I want to know is simple: How many memory do I need for every new router? Do you know a simle rule? What I want to know is the relationship between the number of routes and the memory consumption. I can evaluate know this by looking how many routes are in may routing table and the memory used, but I would appreciate any experience from you. Thanks group! To start out with, the amount of memory is going to depend on the routing protocol(s) in use. But before going farther, be aware that the impact of adding routes impacts more than memory. It will have effects on route processor load, and thus potentially on other functions using that processor. In certain processing architectures, such as the 7000 with silicon or autonomous switching, it can have significant effects on the cache. Purely for memory, you will need 1-2 small buffers per route in the routing table. OSPF, EIGRP, and ISIS all keep databases, which will vary as to the amount of storage needed. Roughly, an LSA takes 300-400 bytes. EIGRP topology tables will be on the order of the size of the routing table each neighbor. In a router with fast switching, you'll also need at least one buffer per cached route. Of course, when you get into the distributed switching modes, there will be VIP memory consumption as well as main processor. BGP will become even more complex because you can have multiple views of the loc-RIB. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=70319t=70299 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
