It is wise to stack the deck in your favor, but you'll never really know how much real redundancy you've purchased:
http://www.atis.org/ndai/ATIS_NDAI_Final_Report_2006.pdf David On Wed, Nov 11, 2009 at 3:41 PM, <a...@baklawasecrets.com> wrote: > I suppose I could take the whole resilience thing further and further and > further. One of the replies used a phrase which I thing captured the problem > quite nicely: "diminishing returns". > Basically I could spend lots and lots of money to try and eliminate all > single points of failure. Clearly I don't have the money to do this and what > I'm really trying to establish is at what > point do the returns start to diminish with regards to obtaining multiple > transit providers. The answer appears to be "it depends". So if getting a > third BGP peering with divergent paths, > separate last mile, separate facility and separate router will increase costs > by 5x but only increase resilience by 0.001% is it really worth it? I'm > trying to quantify the resilience of my > Internet connectivity and quantify the effects of adding more providers. Now > to run through my case: > > - I have one facility to locate BGP routers at. Thats not changing for the > moment. > - I can afford two BGP routers. > - The facility I'm located at tell me they have divergent fibre paths and > multiple entries into the facility. (Still need to verify this by getting > them to walk the routes with me) > - I am going to take transit from two upstreams. > - I could ask the question as to whether I can peer with separate routers on > each of the upstreams. i.e. to protect against router failures on their side. > - I will make sure that neither upstream peers with the other directly. (Does > this give me some AS path redundancy?) > > So from the above: > > - I have no resilience with regards to datacentre location. i.e. if a plane > fell out of the sky etc., I'm done. > - I can afford some BGP router resilience on my side. So I should be able to > continue working if a router failure which only affects one of my routers > occurs. > - I have some resilience in terms of actual fibre paths to the facilites > where I will be picking up the BGP feeds from. (to be verified) > - I have some "AS resilience" if this is the right term. So if the AS of one > of my upstreams drops off the face of the Internet, I can still get to the > Internet through the AS of my other > provider > - Peering with separate routers may give me some resilience for router > failure on the side of my upstreams? (not totally sure on this) > > In this situation, if I add another peering with another upstream, am I > really getting much return in terms of resilience? Or should I spend this > money examining the many other SPOFs in > my architecture? I'm perfectly sure there is absolutely no point me peering > with 6 providers, but maybe some gains in peering with 3? I'm trying to > figure out at what point is adding > another peering in my case a waste of money. > > I haven't gone into switch and power redundancy, because I "think" I > understand it. I wanted to concentrate on the multiple upstreams question. > Heads starting to whirl right about now. > > Adel > > > On Wed 5:27 PM , "Dylan Ebner" dylan.eb...@crlmed.com sent: >> >> You question has many caveats. Just having two providers does not >> necessarily get you more resiliency. If you have two providers and they are >> terminating on the same router, then you still have a SPOF problem. You >> also need to look at pysical paths as well. If you have two (or three) >> providers and they are using a common carrier, then you have a problem as >> well. For example, GLBX has a small prescence in the Minneapolis metro. If >> I were to use them as a provider, they would use Qwest as a last mile. If >> my other provider is Qwest (which it is), I may not have path >> divergence.Facilities are important too. We have three upstreams; Qwest, MCI >> and ATT. >> The facility only has two entrances, so that means two of these are in the >> same conduit. IF you only have one entrance, all you connections are going >> to run through that conduit, and that makes you susceptable to a rouge >> backhoe. >> You are on the right track to question your resilancy. Some upstreams can >> offer good resilancy with multiple feeds. Others cannot. I would start with >> your provider and see what you are getting. Maybe you already have path >> divergence, sperate last miles, and multiple paths in the isp core. If you >> go with multiple providers, you want to make sure you don't risk losing >> something you already have. >> >> >> >> -----Original Message----- >> From: a...@baklawasecrets.com [adel@ >> baklawasecrets.com] Sent: Wednesday, November 11, 2009 11:14 AM >> To: na...@nanog.o >> rgSubject: Resilience - How many BGP providers >> >> >> >> Hi, >> >> After recent discussions on the list, I've been thinking about the >> affectsof multiple BGP feeds to the overall resilience of Internet >> connectivityfor my organisation. So originally when I looked at the design >> proposals, there was a provision in there for four connections with the >> same Internet provider. Thinking about it and with the valuable input >> ofmembers on this list, it was obvious that multiple connections from the >> same provider defeated the aim of providing resilience. >> >> So having come to the decision to use two providers and BGP peer with >> both, I'm wondering how much more resilience I would get by peering >> with more than two providers. So will it significantly >> increase myresilience by peering with three providers for example, as both >> of the >> upstreams I choose will be multihomed to other providers. Especially >> asI am only looking at peering out of the UK. >> >> Hope the above makes sense. >> >> Adel >> >> >> >> >> > > >
