PH> Date: Thu, 11 Mar 2004 18:21:03 +0200 PH> From: Petri Helenius PH> Depending on your requirements, the option of having somebody PH> redistribute all their BGP routes into ISIS or OSPF might not PH> worth looking forward to. Couldn't quite parse this, but it sounds scary. Eddy -- EverQuick Internet - http://www.everquick.net/ A division of Brotsman & Dreger, Inc. - http://www.brotsman.com/ Bandwidth, consulting, e-commerce, hosting, and network building Phone: +1 785 865 5885 Lawrence and [inter]national Phone: +1 316 794 8922 Wichita _________________________________________________________________ DO NOT send mail to the following addresses : blacklist@brics.com -or- alfra@intc.net -or- curbjmp@intc.net Sending mail to spambait addresses is a great way to get blocked.

PH> Date: Thu, 11 Mar 2004 20:31:52 +0200 PH> From: Petri Helenius PH> I�m refering to the most popular way of causing an IGP PH> meltdown. Obviously there are other ways, like software PH> defects to make your IGP go mad. But when your upstream�s IGP PH> does that, you want to have provider B to switch over to. Okay. I was unsure if you were referring to a clueless downstream bloating their IGP, or a clueless transit network redistributing downstream routes. Eddy -- EverQuick Internet - http://www.everquick.net/ A division of Brotsman & Dreger, Inc. - http://www.brotsman.com/ Bandwidth, consulting, e-commerce, hosting, and network building Phone: +1 785 865 5885 Lawrence and [inter]national Phone: +1 316 794 8922 Wichita _________________________________________________________________ DO NOT send mail to the following addresses : blacklist@brics.com -or- alfra@intc.net -or- curbjmp@intc.net Sending mail to spambait addresses is a great way to get blocked.

<On Thu, 11 Mar 2004, Gregory Taylor wrote:

Mutli-homing a non-ISP network or system on multiple carriers is a good way to maintain independent links to the internet by means of different peering, uplinks, over-all routing and reliability. My network on NAIS is currently multi-homed through AT&T. I use a single provider as both of my redundant links via 100% Fiber network. Even though this is cheaper for me, all it takes is for AT&T to have some major outage and I will be screwed. If I have a backup fiber line from say, Global Crossing, then it doesn't matter if AT&T takes a nose dive, I still have my redundancy there.

Well, I think this, in many cases, boils down to being able to pick the right provider. I mean, some providers go belly-up from time to time. Others are designed/run better. For a major provider, complete outage of all of its customers is such a big thing they'll want to avoid it always. If it happens, for a brief moment, once in five years (for example), for most companies that's an acceptable level of risk. -- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

On Thu, 11 Mar 2004, Marshall Eubanks wrote:

There is another thing - if you are multi-homed, and want to switch providers, it is pretty seamless and painless - no renumbering, no loss of connection, etc., as you always have a redundant path.

Sure -- though many ISPs will probably let you keep the address space, even if you switch away completely -- as long as you pay them enough (or the other ISP to route it). Bad practice, but has happened a lot, and probably still does :) FWIW, even if you are multihomed, that does not in and of itself require that you "own" address space. Public AS number is often enough (and even private will do, but that leads to other kind of mess.) -- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

At 4:06 PM +0000 3/12/04, Stephen J. Wilcox wrote:

I think its too easy, thats the problem.

Hoping that I don't sound too much like Bill Clinton, that depends on what you mean by "it." If "it" is multihoming, with your own ASN, to two providers, your raise some valid points. Is there an intermediate alternative before you go all out? Yes, I think so, assuming your current provider has multiple POPs. Let me examine some of your points if we consider RFC 1998-style multi-POPping (I just invented that highly technical term) using PA address space.

For <$1000 (excluding bandwidth/ccts) you can buy a box, connect to your two providers, get an ASN and IPs and you're away.

Alternatively, another POP link, and preferably another router. If you are more concerned with loop failures than router failures, not a completely unreasonable assumption, you could get away with one router that has multiple interfaces, and spend some of the savings on backup power -- possibly a backup power supply in addition to the UPS, such as a Cisco RPS on their smaller routers. While you'll probably take a performance hit, or if you can reduce to critical traffic on an outage, you might get away with a second smaller router.

I dont agree that connecting to two+ upstreams makes you better. In my experience end networks have a couple of orders of magnitude more downtime than a PoP in any reasonably large ISP. Ie the percentage theoretical improvement is small.

Like everything else, It Depends. My experience is that access links fail more often than provider routing systems, especially with a clueful provider. Since you can't guarantee that your physical connectivity to two different ISPs doesn't involve a shared risk group in the lines, there are still some things you may not be protected against. One option, depending on the plant in your area, is that if you are considering a second router, consider putting it in a nearby building, reachable by WLAN (if you are minimizing costs), where that building minimally has different ducts to the telco end office, and ideally goes to a different end office. Not always possible, but to be considered. Longer-range wireless (radio or optical) links get more expensive.

In addition you seriously increase the complexity of your system, chances are you're using the cheapest kit you could find (or at least cheaper and smaller than what I would use).. its not great at BGP and may fall over when you get a minor DoS attack, you probably generate flaps quite a bit from adhoc changes and if you're announcing a /24 then thats going to get you dampened quickly..

That's a motivation for PA address space, where the provider aggregate is less likely to be small and easily damped.

so you actually create a new weakest link. Also most of the corporates I've dealt with take defaults rather than full tables.. so if the provider does have an issue you still forward the traffic, theres no failover of outbound routing.

Again looking at intermediate solutions, there are always partial routes such as customer routes of the provier.

Even if you spend (waste) the money on some decent gear, you're on your own and when a problem occurs the ISPs are going to be less helpful to you (not by choice, I mean they dont have control of your network any more.. there knowledge of whats causing problems is limited to the bit that they provide to you), so chances are your problems may be more serious and take longer to diagnose and fix.

Again, an operational advantage of multiPOPping and working with one carrier, although you aren't going to be protected against insanity of their BGP/

IMHO avoid multihoming. You will know when you are big enough and you *need* to do it, if you're not sure or you only want to do it cause you heard everyone else is and its real cool then I suggest you dont.

MHO would be to look at "multihoming" as a spectrum of solutions rather than a binary choice of single-provider-single-link versus multiple-provider. In given situations, you might also want to look at DSL or cable for diversity, tunneling to an ISP since the broadband provider is unlikely to be willing to speak BGP. Even dialup/ISDN, sometimes for critical workstations, has its place. Shameless plug: I do go through these options in my book, Building Service Provider Networks (Wiley). Even there, though, I only run through the alternatives. You will still have to make your own cost-benefit decisions based on business policy, budget, clue level and cost of alternatives.