Alan Hannan <hannan@bythetrees.com> writes:
AFAICT there is only one orderable, deployable and tested IP router which observably terminates multiple 622-Mbit/s bit pipes, notably that made by cisco.
Hmm, well, the lack of knowledge I suppose shouldn't be held against you.
http://www.ascend.com/505.html
lists their support for such interfaces.
( nonsequiter comments deleted )
I hope the comments privately prior to your writing any of this that pointed out that nowhere in this URL or in Ascend's other literature is the concept of non-ATM 622 mentioned. Oh wait, that's a non sequitur, because it's the same thing as POS, right, only with extra features.
On their head? I can assure you the IGP is still a manageable problem in larger ISPs with meshed backbones. In fact, there is one solution available that is not yet even exercised.
It's only manageable because Henk Smit (and before him Dave Katz) has been going to lots of trouble to clean up all the edge cases strangely flat backbones reveal, and because Cisco has no trouble with the idea of adding in richer metrics to iIS-IS. (Well, neither do I, actually :) ) Really rich connectivity means that it is more work to calculate new forwarding tables as point to point connections come and go, and the results are much harder to predict. Of course, if you take your approach and DON'T route dynamically between routers, but rather reroute VCs around link failures, then you might not have these problems except when fun things happen like ATM switches reloading or router-to-switch failures happen. At that point you have the fun of working out appropriate backup paths for the traffic that used to fan out over a large number of VCs. This is non trivial and scales geometrically with the size of the mesh.
try to avoid thinking too hard about how to build spanning trees without building a physical VC topology for multicast and can put up with interesting buffering and switching effects
Okay, I'll bite: Which interesting buffering and switching effects?
You have to copy datagrams out to each branch of your spanning tree. If you have a largd number VCs out one interface overlaid with a dense spanning tree, you end up with large buffering requirements on that card, or alternatively do funny queue management so that you eat lots of queueing slots if you use an indirection list (i.e., you use pointers pack to the multicast PDU rather than copy the PDU multiple times, however "boxing" datagrams, while it saves memory-to-memory copies can make it difficult to do clever cache prefetching from packet memory, and may not reduce the number of memory reads you have to do, and certainly will increase CPU use). In other words, when using smart line cards like Wellpap or Cisco do, if you are doing lots of multicast with a fairly large distribution, you are better off keeping the spanning tree small. If you have a large number of downstream interfaces on a box, that box works harder. If you have a large number of downstream interfaces on a single card, that card works harder. Harder can be described as larger CPU time and more memory references in some combination, depending on the queueing mechanism and what does the packet copying. Also when you have a large concentration of downward links on a box, that box tends to attract more join and prune messages which also keeps it busier. You could add RSVP issues to that too, if you thought RSVP were somehow relevant to the Universe.
and, as you say, the dynamics of WHY it works vs. why it doesn't work when things break.
Yes, indeed this is a tradeoff.
Obviously you and I have different thoughts about Byzantine failures. I've experienced enough of them driven by multilayer operability issues with a small set of vendors that widening the vendor base substantially (i.e., adding lots of switch vendors and the like, not just adding a second router vendor) or increasing the number of layers which have to interoperate does not appeal much to me.
But, the more I think about the KISS principle, I become convinced that only our own limitations, ignorance, and hesitancy prevent us from adding complexity to achieve increased control.
Sure. How much do you want to spend on NOC staff is a factor in how much complexity NOC staff can handle, and that is a factor in how quickly Byzantine failures can be dealt with. Personally, Byzantine failures that require waking up senior smart people at multiple vendors' companies are scary and as Byzantine failures happen sometimes in big networks, keeping the number of people potentially needed to effect a fix for something really weird strikes me as a win. In short, defensive engineering. Sure complexity seems attractive, but only until your first major meltdown driven directly by or even only exacerbated by that complexity.
I hate to say it but I think I have become old and this might explain why I like really simple and straightforward failure modes.
See above comments.
See bags under eyes and many scars.
Yes, we at 'bythetrees.com' are avid supporters of ATM in today's technology.
Oh sure, you're bythetrees.com NOW. --:)
Why do you always insist on linking one's place of business with their technological idealogy?
Because: a) it makes people angry, and that's really funny b) it reminds people whom they are working for and what trade-offs they make between what they want and what their employers say they want c) a + b sometimes causes people to fix their employers into doing things "correctly", or leads people into realizing their employers are hopeless and that there are other opportunities elsewhere (which sometimes also fixes the employer) the latter part of (c) is particularly edifying if it involves physical violence to doors and so forth. So, needle needle, if you are at variance with UUWHO's technical policies, why are you still there?
Certainly I work at UUNET and my opinion is occasionally involved in certain decisions.
Oh, cool, so I can blame you for brain damage. Several managers will be really happy now that you've volunteered yourself to be picked on in technical lists instead of them. :-)
Hmm, I tend to be atheistic about technology -- what can it do for me today, and what will it to do tomorrow with a reasonable chance of success.
I think you mean agnostic, not atheistic. I distinctly remember you comparing me to Jesus Christ.
There may be choice in what you can put at the end of an OC12 though, but it's either something smart or something you'd find at Hobson's Tavern.
How do you define smart?
When you put your brain into a blender and unpack it into individual cells in hopes you can put it all back together the way it was without having noticed, that's not very smart. Sean. (don't send the next cheesecake as breadcrumbs please :-) )
AFAICT there is only one orderable, deployable and tested IP router which observably terminates multiple 622-Mbit/s bit pipes, notably that made by cisco.
http://www.ascend.com/505.html lists their support for such interfaces.
I hope the comments privately prior to your writing any of this that pointed out that nowhere in this URL or in Ascend's other literature is the concept of non-ATM 622 mentioned. Oh wait, that's a non sequitur, because it's the same thing as POS, right, only with extra features.
I see now where we missed each other -- no, I know of no POSIP interface for OC12 with the exception of Cisco's. However, as it is not a tool that I can put into my great big bag of router tricks (with the exception of peerings or customer connections, which I'm pondering) it's not too important (to me) (right now). We differ in this manner -- you feel the negatives of atm forbid its use *period*, while I think its benefits outweight any negatives at this time, and couldn't consider growing a large network without its flexibility.
On their head? I can assure you the IGP is still a manageable problem in larger ISPs with meshed backbones. In fact, there is one solution available that is not yet even exercised.
It's only manageable because
But it's manageable.
because Cisco has no trouble with the idea of adding in richer metrics to iIS-IS. (Well, neither do I, actually :) )
Funny you and cisco agreeing. Nonetheless, the metric set is its own problem, but moderately orthagonal to any of these discussions. On that tangent, however, flooding is what we're mostly concerned about, and it's just not that bad.
Of course, if you take your approach and DON'T route dynamically between routers, but rather reroute VCs around link failures, then you might not have these problems except when fun things happen like ATM switches reloading or router-to-switch failures happen. At that point you have the fun of working out appropriate backup paths for the traffic that used to fan out over a large number of VCs. This is non trivial and scales geometrically with the size of the mesh.
The scaling issue is synonymous w/ an entirely L3 network. L2 networks just put it off and make it somewhat less likely. See, I get the impression that people on this list can be categorized as two kinds -- router people and network people. That may be too strict a delineation.
multicast and can put up with interesting buffering and switching effects
Okay, I'll bite: Which interesting buffering and switching effects?
(paragraph about buffer:flow ratios deleted) Hmmm. So how does this change by putting lots of virtual interfaces on a router and putting the buffering into L2?
and, as you say, the dynamics of WHY it works vs. why it doesn't work when things break.
Yes, indeed this is a tradeoff.
Obviously you and I have different thoughts about Byzantine failures. I've experienced enough of them driven by multilayer operability issues with a small set
Perhaps it's a difference in the quality or quantity of those managing the network. ;-) The interoperability adds a variable, but the scalars in the equation minimize probability or problems.
of vendors that widening the vendor base substantially (i.e., adding lots of switch vendors and the like, not just adding a second router vendor) or increasing the number of layers which have to interoperate does not appeal much to me.
That's why you do it your way and.....
But, the more I think about the KISS principle, I become convinced that only our own limitations, ignorance, and hesitancy prevent us from adding complexity to achieve increased control.
Sure. How much do you want to spend on NOC staff is a factor in how much complexity NOC staff can handle, and that is a factor in how quickly Byzantine failures can be dealt with.
Yep.
Personally, Byzantine failures that require waking up senior smart people at multiple vendors' companies are scary and as Byzantine failures happen sometimes in big networks, keeping the number of people potentially needed to effect a fix for something really weird strikes me as a win.
In short, defensive engineering.
At the cost of scalability. Not a win. Anytime you limit growth to a variable you are doomed (ahh physical space you evil beast). Instead, you educate and.... this thread goes nowhere. I see your point, we disagree.
Sure complexity seems attractive, but only until your first major meltdown driven directly by or even only exacerbated by that complexity.
The opportunity to have a complex network is arift with its own problems. Once your problem set becomes large enough your solution set becomes larger. Increase your richness in variables to solve more quickly and exactly.
Why do you always insist on linking one's place of business with their technological idealogy?
Because:
a) it makes people angry, and that's really funny b) it reminds people whom they are working for and what trade-offs they make between what they want and what their employers say they want c) a + b sometimes causes people to fix their employers into doing things "correctly", or leads people into realizing their employers are hopeless and that there are other opportunities elsewhere (which sometimes also fixes the employer)
the latter part of (c) is particularly edifying if it involves physical violence to doors and so forth.
So, needle needle, if you are at variance with UUWHO's technical policies, why are you still there?
I don't accept your assertion, but in answer to the latter query: They/We rock. :-)
Hmm, I tend to be atheistic about technology -- what can it do for me today, and what will it to do tomorrow with a reasonable chance of success.
I think you mean agnostic, not atheistic.
No, I mean atheistic. I am without religion with regards to L2 fabric selection for networking. You want to believe (smith's reference), but you're just not sure. I don't believe, I rely on facts. You do too, but you ignore some facts because of your religious tendencies.
I distinctly remember you comparing me to Jesus Christ.
Yes, remember the crucifix phrase?
There may be choice in what you can put at the end of an OC12 though, but it's either something smart or something you'd find at Hobson's Tavern.
How do you define smart?
When you put your brain into a blender and unpack it into individual cells in hopes you can put it all back together the way it was without having noticed, that's not very smart.
Hmm, I thought that's what telnet did to keystrokes gifs. Or what sonet did to PPP or whatever those l2 things are that the cisco OC12 interface sends out. Or what web servers did to IP when they send noodie gifs to pedophiles using PGP.
Sean. (don't send the next cheesecake as breadcrumbs please :-) )
You owe me. I'll take a pound of cheese to go with your next mail. :-) -alan ps. for those of you at home or work forced to endure this anecdotal parenthetical, I used to work at a particular NSP who used Sean's previous employer for internet connectivity. His always happy and never wavering commitment to customer service and reliability soon found us cheerful chums. In thanks to this level of service, I bestowed a cheesecake to him from a customer of ours at the time. I was not reimbursed for this from my company, but I guess it's too late....
participants (2)
-
Alan Hannan -
Sean M. Doran