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Re: The Cidr Report

  • From: Warren Kumari, Ph.D, CCIE# 9190
  • Date: Sun Feb 13 20:58:50 2005

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On Feb 13, 2005, at 6:19 PM, Christopher L. Morrow wrote:

On Sun, 13 Feb 2005, Michael Smith wrote:
From: "Warren Kumari, Ph.D, CCIE# 9190" <[email protected]>
On Feb 13, 2005, at 2:31 AM, Christopher L. Morrow wrote:

That and the "I have 1 circuit to $good_provider and 1 circuit to
$bad_provider and the only way I can make them balance is to split my
space in half and announce more specifics out through each provider"
argument. I have also often seen people do this without announcing the
aggregate because <some undefined bad thing> will happen, usually
justified with much hand-waving. The people who do this can usually
not be reasoned with....
So, say I'm a provider that has received a /22 from UUNet (just for example
Chris :-) ) and I now get another transit provider and announce the /22
there. So, I call UUNet and ask them to announce the /22 as a more specific
Meaning you have PA space from UUNET, and you have BGP so you can
multi-home... I'd expect you to know how to deaggregate yourself. You
MIGHT even know how to send no-export on deaggregated prefixes, or use the
1996 policies to influence preferences/prepends internal to 701, yes?

because I don't want a de-facto asymmetric configuration. I *want* to get a
/20 from ARIN but my usage doesn't justify it yet, so I have to ride the /22
for some time.

I'm not clear as to how the /22 to /20 discussion goes, or how it's even
relevant... but it's been a long day. Can you elaborate?

By the long string of anecdotal attacks in the string to date, listing most
or all such providers as "bad" or "uninformed" how do you separate out those
providers who are legitimately interested in routing redundancy and not clue
a /22 in both directions seems like safe 'redundancy'. Adding no-export
/24's or /32's if you want (yuck) would get you more preference inside one
provider or the other.

I'm also fairly sure I didn't say: "bad" or "uniformed" the 'bad provider'
is from Warren, not I.
Whoops, I guess I wasn't very clear. By $good_provider and $bad_provider I wasn't meaning to imply that $good_provider ran their network "better" or
"cleaner" than $bad_provider, merely that (by default and without tuning) more traffic travels via $good_provider than via $bad_provider (e.g. $bad_provider buys transit from $good_provider). I guess I should have used big_provider and little_provider or something.

impaired? Do we just say "too bad, routing table bloat is more important
than your need for redundancy small guy!"?
No, I don't think anybody was saying that, just that many people are needlessly de-aggregating space. I have seen someone with a single T3 (and obviously a single provider!) announcing his PA /19 as a bunch of /24s, redistributed into BGP from OSPF! Some consultant had come in, set it up and left. After a bit of help, said person turned off BGP and has been running fine ever since. No-one was trying to take away your redundancy, just limit the number of unnecessary announcements. See Chris's comments above on how to get redundancy without making others pay for it....

I think that folks have been pushed toward multihoming with multiple
providers (not just 'redundant T1' or 'shadow T1' services inside the same
provider) over the last few years. That means some bloat is bound to
occur. I'm not measuring it myself, but the renesys folks and LCS folks
have been I think? Perhaps they can comment on that phenomenon?

I find it interesting that the general theme is one of "we're smarter than
they are because we aggregate more routes" as if clue were directly
correlated to aggregated routing announcements.
Well, often lack of aggregation is directly caused by lacy of clue. Obviously there are legitimate reasons for de-aggregating a big block (otherwise we would all just carry 0/0 :-) ) but if there is no additional information in the more specifics, then there is no reason for them the be announced.

it's not? :) (joking of course) As I said before some folks feel they have
a legitimate reason for deaggregating. If you can spend some time chatting
them up about their reasons and either:
1) realizing they hav a point
2) re-purpose their thoughts toward 'better cidr management' (as pfs said)

then good for you... and everyone else :) I have spent sometime on
occasion doing this, sometimes it works out, othertimes it doesn't :( It's
always an experience though.
It certainly is...


- -- Militant Agnostic--I don't know and you don't either!
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