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Re: Reverse DNS and SMTP
by Conrad A. Rockenhaus 28 Feb '02

28 Feb '02

Patrick Muldoon <doon(a)inoc.net> said: > > If an ISP who doesn't have reverse DNS setup correctly on their > mail servers, we point them to the RFC's and generally offer to help > them correct it. > We have noticed that our spam has reduced drastically, and the > complaints are few, but alas this is a double edged sword, where if you > even block 1 legitimate e-mail out of the 100K+ that we receive daily, > someone is going to complain. To be honest, I would do this as a last resort. For example, if their ISP's (or their own, if they have the block delegated) DNS server is misconfigured, etc, you might have a issue. Also, some admins have no clue what reverse dns is, seriously :). I would use a service like MAPS first to see if that resolves the issue, and use this as a last resort. If they don't have an issue with blocking unresolvable ips, then they shouldn't have an issue with just using an rbl ;). --conradr

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RE: Reverse DNS and SMTP
by Pete Stephenson 28 Feb '02

28 Feb '02

>A better solution is to check the ip and see if it is an MX record for >the domain the mail purports to be from. [de-lurk] Perhaps, but do recall that there are systems out there which have certain servers listed in the MX records for receiving mail, and different servers for sending mail that aren't listed in the MX records. You can't please everybody, I guess. Apologies to Daniel, as he would receive two copies of this message. -- Pete Stephenson HeyPete.com

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Re: Satellite latency
by Mark Allman 28 Feb '02

28 Feb '02

> > if you adjust the window size on the sending and receiving > > systems, you can improve this, but this solution is impractical, > > as you would need to get everyone on the internet (or at least > > all of the webservers and websurfers you are servicing) to make > > adjustments to their local TCP stack. > > The receiver is the one that informs the sender how large of a > window it can accept, so it can be practical for a subscriber > installation. It wouldn't be a good idea to park a bunch of > servers behind one of these links, but any receiving node that set > its TCP receive window to 2x the byte/sec capacity of the link > should see decent throughput. No, you need to set things on both sides. The sender has to buffer data until it is ACKed in case it needs to retransmit. So, its buffer needs to be as big as the advertised window or the sender buffer will effectivly limit the advertised window. allman -- Mark Allman -- NASA GRC/BBN -- http://roland.grc.nasa.gov/~mallman/

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Re: Satellite latency
by Jim Mercer 28 Feb '02

28 Feb '02

On Thu, Feb 28, 2002 at 12:14:43PM -0500, Eric Oosting wrote: > Is there something else specific to one-way satellite connections that you > are attributing these problems with asymmetric routing to? There is > nothing inherently wrong with asymmetric routing that causes high latency > or perceived differences in usability of real-time connections like ssh. > For instance, a large percentage of the traffic on the Internet is > asymmetric. Anyone who is multihomed knows that half the time they send > something to one upstream, it will come back a different upstream. > > Do you believe that there is something wrong with a downlink of 400ms and > an up of 100ms? (guesses at satellite with dialup return connection one > way latencies) I can't imagine that things would be better with a 400ms > down and 400ms back up (as with a two-way sat connections) but maybe you > can do different tricks with spoofing tcp acks to the traffic over the sat > link when it is two-way. in my experience, the upstream, typically via terrestrial, is more lossy than the downlink. this has nasty effects on ssh windowing. i haven't used telnet in a long time, more specifically over sat links. asymetric traffic over high-speed, low latency, low loss links is mostly transparent. when one path is clean, and the other is dirty, then the symptoms get worse. also, asymetry is relative. in one case, i had packets go high speed across north america (uunet/teleglobe/ sprint/alternet/etc/etc) over unencumbered fiber to the UK, then up via satelite, down into the middle east into a terrestrial fiber network to the dial-up port to the user. the return path was dial-up over ancient infrastructure, to an overloaded national backbone provider, via overloaded circuits to singtel, across the pacific (using different networks depending on the phase of the moon), into north america. this is wholly different from have the outgoing packet traverse teleglobe from newyork->los-angeles, and having the return packet go via alternet from los-angeles->newyork. (although, depending on the phase of the moon, sometimes teleglobe and/or alternet resemble the previous paragraph). 8^) -- [ Jim Mercer jim(a)reptiles.org +1 416 410-5633 ] [ I want to live forever, or die trying. ]

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Line Rate vs CPU utilization info requested
by Donn Lasher 28 Feb '02

28 Feb '02

Does anyone have a table / web site / etc that talks about realized IP throughput on various routers (3600 / 7100 / 7200, 5500, 6500, etc) versus cpu load? IE even though you can put 4 x 100M ethernet cards in a 3640, IMHO, you'd never see 400/800M aggregate throughput because the CPU would be on its' knees begging long before that point. I'm looking at a project that calls for a DS3, and the suggested router is a 3640, and I'm trying to prove / document that's not a wise idea. What has your experience been? Anecdotal or personal experience appreciated. Offline replies work just as well. Thanks in advance. -donn

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RE: Satellite latency
by Rowland, Alan D 28 Feb '02

28 Feb '02

Not to mention that -5 degree or so look angle (negative elevation) from the poles being hard to acquire. ;) But with enough elevation and a big enough dish... Also about that satellite drift...The earth wobbles during rotation meaning geo stats do small figure 8s overhead. IIRC there is some computer software out there (from my days of TVRO in Europe) that given a latitude/longitude and sat placement would return a time where the sat was in the middle of that 8 so you could best aim the dish. Or maybe I just had too much Heineken at the bar, can't remember which. Just my 2¢. The delete key is your friend. -Al -----Original Message----- From: Michael Painter [mailto:tvhawaii@shaka.com] Sent: Wednesday, February 27, 2002 12:22 PM To: nanog(a)merit.edu Subject: Re: Satellite latency ----- Original Message ----- From: "Leo Bicknell" <bicknell(a)ufp.org> To: "Steven M. Bellovin" <smb(a)research.att.com> Cc: "Tim Devries" <zsolutions(a)cogeco.ca>; <nanog(a)merit.edu> Sent: Tuesday, February 26, 2002 5:27 PM Subject: Re: Satellite latency >>Remember that a geosynchronous satellte must orbit the equator. Let's say for the sake of argument it's over mexico, you're in New York, and the downlink station is in San Diego. The 36,000 is the distance straight "down" to mexico, It's probably more like 50,000 to New York, and 45,000 to San Diego. And if you're in New York, and your mail server is in New York, but the downlink was to San Diego, you've got another 4,000 across country. Now you're up closer to 100,000km.<< Not wanting to get picky about ~20,000 km., but the maximum -usable- slant path is ~41,000 km. --Michael > > In a message written on Tue, Feb 26, 2002 at 09:07:14PM -0500, Steven M. Bellovin wrote: > > Geosynchronous orbit is about 36,000 km from the center of the earth. > > Round-trip to the satellite is ~72,000 km; the speed of light is > > 300,000 km/sec. That works out to 240 milliseconds at the minimum for > > one-way packet delivery. > > Remember that a geosynchronous satellte must orbit the equator. > Let's say for the sake of argument it's over mexico, you're in New > York, and the downlink station is in San Diego. The 36,000 is the > distance straight "down" to mexico, It's probably more like 50,000 > to New York, and 45,000 to San Diego. And if you're in New York, > and your mail server is in New York, but the downlink was to San > Diego, you've got another 4,000 across country. Now you're up > closer to 100,000km. > > Add to this some inefficient encoding done on satellites, and most > (consumer) systems using a broadcast medium that can buffer packets > and you see why people report 1 second RTT's with services like > StarBand. > > It's better than nothing, but it's a rough primary connection. > > -- > Leo Bicknell - bicknell(a)ufp.org - CCIE 3440 > PGP keys at http://www.ufp.org/~bicknell/ > Read TMBG List - tmbg-list-request(a)tmbg.org, www.tmbg.org >

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RE: Just keep telling yourself, "Worldcom won't fail, Worldcom wo n't fail"
by Jon Stanley 28 Feb '02

28 Feb '02

What is the reasoning for thinking that WorldCom may fail? Is there something that I've missed? -----Original Message----- From: Fletcher E Kittredge [mailto:fkittred@gwi.net] Sent: Monday, February 25, 2002 12:51 PM To: nanog(a)merit.edu Subject: Just keep telling yourself, "Worldcom won't fail, Worldcom won't fail" This is an interesting NYT article (free registration required) for all of those of us trying to convince themselves that even if Worldcom goes bankrupt, UUnet will stay up. The example used is Global Crossings. If a company has complex enough finances and gets deeply enough under water, the courts might not be able to figure it out and creditors may just liquidate... whether or not it makes sense for the customers and society as a whole. If the government is not willing to step in for Enron, would they step in for UUnet? http://www.nytimes.com/2002/02/25/technology/25GLOB.html By the way, I never said to Dan Hollis and others: "You were right; I was wrong." about Global Crossing. If one had listened to Dan, one would have known 12 months that Global Crossing was in trouble. I read their press releases and balance sheets and didn't see it... Mea Culpa. regards, fletcher

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Re: Satellite latency
by Steven M. Bellovin 28 Feb '02

28 Feb '02

In message <014d01c1bf3b$44bfca00$ea9a8d18@evilinc>, "Tim Devries" writes: > >Hello, > >I think this question may have been asked before, but what is the minimum >latency and delay I can expect from a satellite connection? What kind of >delay have others seen in a working situation? What factors should be >considered in end to end connectivity architecture when utilizing a >satellite link? > >Any help appreciated, Geosynchronous orbit is about 36,000 km from the center of the earth. Round-trip to the satellite is ~72,000 km; the speed of light is 300,000 km/sec. That works out to 240 milliseconds at the minimum for one-way packet delivery. --Steve Bellovin, http://www.research.att.com/~smb Full text of "Firewalls" book now at http://www.wilyhacker.com

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Re: Fiber cut in Anaheim?
by Stephen Fisher 27 Feb '02

27 Feb '02

MCI says that there are 8 OC48's down in a fiber cut due to utility company cutting through the conduit. No ETA. On Wed, Feb 27, 2002 at 04:35:11PM -0500, Eric Whitehill wrote: > > NANOG: > > I have some customers reporting a possible fiber cut in/near Anaheim, CA. > Anyone able to confirm/deny/throw donuts at this? > > Thanks, > > -Eric

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Fiber cut in Anaheim?
by Eric Whitehill 27 Feb '02

27 Feb '02

NANOG: I have some customers reporting a possible fiber cut in/near Anaheim, CA. Anyone able to confirm/deny/throw donuts at this? Thanks, -Eric

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