Those /24s likely have something to do with the fact that the blocks in the
A space you
mentioned are ARIN allocated CIDR blocks. I believe that ISPs tend to be a
little less
restrictive on them. Several other route-servers mirror your findings on
cerf.net.
For those of you that haven't seen it:
http://www.arin.net/regserv/IPStats.html#cidr
--trey
Chuck Larrieu wrote:
> I respectfully disagree. A brief look through route-server.cerf.net shows
an
> awful lot of /24's in class A space, particularly in the 24.0.0.0,
64.0.0.0,
> 65.0.0.0, and 66.0.0.0 space. Not to mention a lot in class B space. My
hand
> hurts from scrolling through the routing table there. Granted, everything
is
> relative. What cerf.net shows is not necessarily what any other provider
> shows. But I suggest that CIDR is broken and there are lots of prefixes
> longer than /19, no matter what the classful block. :->
>
> Chuck
>
> -----Original Message-----
> From: Brian [mailto:[EMAIL PROTECTED]]
> Sent: Monday, May 07, 2001 5:05 PM
> To: Chuck Larrieu
> Cc: [EMAIL PROTECTED]
> Subject: RE: real world BGP question [7:3506]
>
> many providers filter based on the classful origin of the space. If the
> block is out of what was once class a or b space, the likelihood of a /24
> getting filtered out is fairly high. My previous employer did that.
>
> Brian "Sonic" Whalen
> Success = Preparation + Opportunity
>
> On Mon, 7 May 2001, Chuck Larrieu wrote:
>
> > Seems rather presumptuous of Cisco to speak for every ISP in the
world....
> >
> > In order to limit the number of routes being advertised on the internet,
I
> > believe it was considered "best current practice" to limit prefix length
> to
> > /19 or shorter. ( can't find the RFC at the moment, but I recall it being
> > referenced several times in various threads on the NANOG list. )
> >
> > Obviously, with well over 100K routes in "the internet routing table"
> there
> > are a great number of longer prefixes being advertised, no doubt in great
> > part because of the number of companies that are "connected to multiple
> > ISP's so they can load balance across the internet"
> >
> > Prefix advertising my be influenced by peering arrangements, downstream
> and
> > upstream agreements, and customer requirements. Generally, once holes are
> > punched through CIDR blocks, what can anyone do?
> >
> > When someone makes a statement like you attribute to Cisco, one must
> always
> > follow up with specifics to determine what is really meant. Not all
routes
> > seen in one provider's network routing tables are necessarily present in
> the
> > tables of another provider.
> >
> > Chuck
> >
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> > Murphy, Brennan
> > Sent: Monday, May 07, 2001 4:01 PM
> > To: '[EMAIL PROTECTED]'; Charlie Winckless; Murphy, Brennan
> > Cc: [EMAIL PROTECTED]
> > Subject: RE: real world BGP question
> >
> > Cisco told me today that a /24 drawn from Class C space
> > has a better chance of being propogated throughout the Internet
> > than a /24 taken from Class B space. Anyone disagree with that?
> > Can anyone recommend a good source of info on this. Ive checked
> > Halabi.
> >
> > I came across a good reference during my quest www.traceroute.org
> > Unfortunately, it doesnt offer plain answers to my questions.
> >
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> > Sent: Friday, April 27, 2001 1:58 PM
> > To: Charlie Winckless; 'Murphy, Brennan'
> > Cc: [EMAIL PROTECTED]
> > Subject: Re: real world BGP question
> >
> >
> > Currently on a US basis a /24 would generaly work. Internationaly
> (Europe)
> > most providers would filter out anywhing longer then /20.
> >
> >
> > ----- Original Message -----
> > From: "Charlie Winckless"
> > To: "'Murphy, Brennan'"
> > Cc:
> > Sent: Friday, April 27, 2001 1:18 PM
> > Subject: RE: real world BGP question
> >
> >
> > > I used to work for VERIO. At that time they would not
> > > router smaller than /19 on their backbone.
> > >
> > > This may have changed.
> > >
> > > > -----Original Message-----
> > > > From: Murphy, Brennan [mailto:[EMAIL PROTECTED]]
> > > > Sent: Friday, April 27, 2001 10:46 AM
> > > > To: 'Michelle T'; '[EMAIL PROTECTED]'
> > > > Subject: RE: real world BGP question
> > > >
> > > >
> > > > I guess that is my real question: what is the longest prefix that
> > > > is exchanged among/between major carriers.
> > > >
> > > > The real world example here is what if you had 4 server farms
> > > > answering
> > > > to one DNS name: ftp.foo.com You have Round Robin DNS running
> > > > round trip times to match a user with their nearest server farm....
> > > > so it sends back the closest/fastest IP. The question is, how
> > > > big do those
> > > > subnets for the server farms have to be in order to be maximally
> > > > advertised throughout the internet?
> > > >
> > > > So, I've seen two answers in this thread /20-21 or /24. I wonder
> > > > where I could find the real answer? Maybe Halabi has a link in the
> > > > back of his book to an organization that maintains info such as
> > > > this.
> > > >
> > > > Any more input is greatly appreciated. Thanks to all who have
> > > > responded.
> > > > I figured this question was a relavant BGP question relating
> > > > our studies
> > > > to an actual scenario.
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: Michelle T [mailto:[EMAIL PROTECTED]]
> > > > Sent: Friday, April 27, 2001 12:06 PM
> > > > To: Murphy, Brennan; [EMAIL PROTECTED]
> > > > Subject: RE: real world BGP question
> > > >
> > > >
> > > > /24 is the longest prefix you will see accepted by nearly any
> > > > carrier out
> > > > there. Many will only accept /20 or /21. All perform
> > > > aggregation to some
> > > > degree, though exception routing is allowed to send the /24's
> > > > (/23, /22,
> > > > etc) out to the ISP peers when the customer is multi-homed two
diverse
> > > > carriers.
> > > >
> > > > I can tell you that I work for a Tier 1 ISP and we accept
> > > > longer prefixes
> > > > for many customers who are multi-homed just to us. They use
> > > > the various
> > > > subnets as a simple method of controlling inbound traffic
> > > > distribution, to
> > > > enact policy, etc...
> > > >
> > > > Many times we see multi-homed (dual-ISP) customers advertise
> > > > an aggregate
> > > > /16 or longer and also advertise /24's for the same reaason (policy,
> > > > distribution, etc).
> > > >
> > > > Michelle Truman
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf
Of
> > > > Murphy, Brennan
> > > > Sent: Friday, April 27, 2001 10:28 AM
> > > > To: '[EMAIL PROTECTED]'
> > > > Subject: real world BGP question
> > > >
> > > >
> > > > What is the smallest subnet that major carriers will exchange with
one
> > > > another? /24..../26.../27?? I know that the real issue is
> > > > the size of
> > > > the route table.
> > > >
> > > > I'm just wondering about the reallity of scenarios that
> > > > Habali describes
> > > > where an institution advertises an aggregate with specific subnets.
> > > >
> > > > I know that when you're multi-homed to a carrier, that carrier will
> > > > sometimes
> > > > take your /26 and /27 nets to help route inbound traffic but
> > > > that carrier
> > > > will not advertise those nets to its neighbors.....at least
> > > > thats what I've
> > > > heard.
> > > >
> > > > Anyone have any real world experience with this? Or is there a URL
> > > > I could read up on?
> > > >
> > > > Thanks,
> > > >
> > > > BM
> > > > **Please read:http://www.groupstudy.com/list/posting.html
> > > > **Please read:http://www.groupstudy.com/list/posting.html
> > > **Please read:http://www.groupstudy.com/list/posting.html
> > **Please read:http://www.groupstudy.com/list/posting.html
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