Can’t comment on “small iron” routers as limited experience but can tell you with larger gear (which in theory has a lot more CPU/processing capability) that large OSPF networks (100k routes) exist and work just fine. One company I consulted for a number of years ago had over 600k routes in OSPF .. seriously … and yes they did experience some issues but they were not big enough issues to warrant changing til a few years later when they migrated everything to ISIS anyways. That’s the most extreme example and not one I personally recommend 😉
As others have mentioned, it’s a hard question to answer as there is no “one size fits all” … often it’s more about how the network is designed then specific sizes of routes or numbers of routers… Paul From: Af <af-boun...@afmug.com> on behalf of Eric Kuhnke <eric.kuh...@gmail.com> Reply-To: <af@afmug.com> Date: Thursday, June 7, 2018 at 6:06 PM To: <af@afmug.com> Subject: Re: [AFMUG] OSPF - How large can a flat network grow? Also worth mentioning that a lot of OSPF documentation available on the Internet, makes assumptions that were valid in 2002 or so... When a typical router had a lot less DRAM and CPU. Such as a Cisco 3725/3745 or even something smaller like a 2621. Probably still true if you're trying to do OSPF on very small Mikrotiks but not as much of a concern in the modern era. The main bottleneck in routing platforms is FIB size and RAM for BGP tables, not so much OSPF. On Thu, Jun 7, 2018 at 1:15 PM, Dennis Burgess <dmburg...@linktechs.net> wrote: This is a “unanswerable” question. In honesty, you can have 20k routes in OSPF and it be responsive so the routing platform does not have a limit. The number of routers, is another issue, if you have 500 routers all fiber connected and they don’t go up/down much, then no big deal, however, if they do go up down quite a bit or you don’t know how to manage them, then yes this can be a factor. The last thing is convergence time, if you have lots of fiber, and/or well connected routers, then that is not a major issue, break part of your network and see how long it takes for a reroute, if that is acceptable, then again no worries. Now OSPF books, state that you should have no more than 75-100 routers, but I have read things that state no more than 50 and I have other networks that have more than 500. So.. Again, it’s not a good answerable question. However, my suggestion is to look at your network as a whole and see if there is some kind of logic, to splitting up your OSPF domains. You can use OSPF areas, or you can use BGP between them. But there needs to be a good, constant method to splitting your network like that. Keep in mind that using defaults will cause traffic to shift, etc, so you need to plan plan plan… Just my two cents. Dennis Burgess, Mikrotik Certified Trainer Author of "Learn RouterOS- Second Edition” Link Technologies, Inc -- Mikrotik & WISP Support Services Office: 314-735-0270 Website: http://www.linktechs.net Create Wireless Coverage’s with www.towercoverage.com From: Af <af-boun...@afmug.com> On Behalf Of Brough Turner Sent: Thursday, June 7, 2018 1:41 PM To: af@afmug.com Subject: [AFMUG] OSPF - How large can a flat network grow? We're an urban WISP with a dense mesh of wireless links and a router per building. I am concerned that, without paying attention, we have grown to 600+ routers and ~2550 routes in one OSPF domain. This network has a diverse mix of routers from CCR1036s down to RB750UPs. We're not having any OSPF problems at this time and I have plenty of other things to worry about, but I'd hate to hit some limit and have the whole thing blow up. Does anyone have experience (positive or negative) with large flat OSPF networks? And, if you have had problems, what were the problems? Thanks, Brough Brough Turner netBlazr Inc. – Free your Broadband! Mobile: 617-285-0433 Skype: brough netBlazr Inc. | Google+ | Twitter | LinkedIn | Facebook | Blog | Personal website
