Query: What policies do backbone providers use to determine IP ownership?

Tony Mumm tonym at netins.net
Wed May 23 16:46:47 UTC 2001

Hash: SHA1

I certainly agree with your statements that customers want to
multihome, and that we will have to accommodate them.  It is
quite reasonable, and we encourage it where high availability is

I will also accept that renumbering can be a great amount of work
for a customer.   I think that amount of work, however, is quite
justified if the customer has received portable space from the
registrar.  I think the customer would be just as motivated to
get out of ISP provided IP space...just to be flexible the day
they decide to add/drop a provider.

On the technical front, with routers being what they are, I can
see that we are not in danger of hurting core routers with bloat.
Well, most of us anyway...I know of small shops that have had to
swap for more memory, etc as the table grew.  I can now say that
their method of multihoming is the whole reason they need to buy
a new router (just kidding).

Secondary to that however, is that if I don't know what's
happening with the customer, how can we set this up correctly.
If no BGP peering session exists for that customer, they will
announce their smaller block as the only path, until its
withdrawn and only the CIDR remains.  This is where I feel the
word hijacking applies.   We would work with them to set it up
correctly so an AS path for this smaller block is passed through
us as well as the other customer.

I guess it comes down to etiquette in the end.  If I whois the
block, and its non-portable space allocated to someone, I feel
they should know I'm going to announce it.  This may have
technical repercussions on their network that they may want to
know about.

Customer education about the policies of the ISP who allocates
the IP space certainly will help I think, however customers
(bless their soul) will often do what suits them best regardless
of policies.   Knowing the policy is probably the only way to
have reproach if a problem situation comes up.

The only check and balance in this whole process is the person
that is adding the route to their accept policies.   It seems a
small inconvenience to check with the owning provider, and a
great courtesy to both ISPs.

In the end, communication will not only benefit the ISP, but also
the customer in the form of better routing (and understanding).

- -----Original Message-----
From: Daniel Golding [mailto:dan at netrail.net]
Sent: Wednesday, May 23, 2001 11:14 AM
To: Tony Mumm; nanog at nanog.org
Subject: RE: Query: What policies do backbone providers use to
IP ownership?

Customers want to be able to multihome. This is not an
unreasonable desire,
and it is what they are, ostensibly, paying us  for.

Your main complaint seems to be advertisement of individual
netblocks from
larger aggregates. While this does contribute to the growth of
the internet
routing table, this is an artifact of the way routing processes
and BGP
work, rather than any fault from your customers. What are your
options for multihoming?

1) Advertise smaller blocks out of larger aggregates to other
2) Get their own, PI space, and advertise it - if they are large
enough to
obtain it. Of course, this causes one or more additional route
as well.
3) The customer sucks it up, and sticks with a single provider

Clearly, most customers are going with #1 or #2, which will
increase the
size of the routing table. They can minimize this by renumbering
consecutive address space, but that assumes that this greatly
disrupt their
business, and that they can indeed get a quantity of consecutive
space from
an upstream.

"It seems that other providers are allowing our customers to
hijack our
routing space piece by piece."

Is your complaint that other providers aren't calling you to get
to route your space? Although there may be some disagreement on
etiquette of routing other provider's blocks, if someone has a
block swip'ed
to them, that's pretty much license to route that block through a
provider, unless the policy of the original provider specifically
it. And in that case, the duty is on the customer to know his
policies, rather than on the second provider to somehow research
policies of the first provider. Of course, in the absence of
WHOIS information stating that a customer has the right to
advertise a
block, it's wise to get written permission from the "owner of the

The routing table will increase in size, as the number of issued
AS numbers
go up, as multihoming increases, as new address space is
However, current core router hardware is more than capable of
dealing with
this growth. I certainly encourage customers to aggregate
wherever possible.
However, requiring renumbering is a heavy, and unnecessary

Multihoming has become part of basic transit service

- - Daniel Golding

Tony Mumm Said....
> All,
> I'm curious to what extent everyone is checking to determine
> ownership of IP addresses when taking on new customers.
> Lately, multi-homing has become a very hot topic for even the
> smallest of providers.  With that, customers are bringing along
> their IP addresses from their previous providers.   Are we
> required, as providers, to determine if that block is actually
> owned by that customer, and facilitates good Internet routing?
> I've seen a trend lately where I'm finding out, after the fact,
> where pieces of larger CIDR blocks are being taken apart by a
> myriad of unaggregated routes.   The other backbone providers
> freely allowed an announcement of that non-portable space to
> Internet without regard to either the owning provider, or to
> general Internet routing.
> My concern is two fold:
> 	1)	This contributes to terrible Internet routing.  By not
> addressing this with the customer 			right away,
> we'll continue
> to deal with a proliferation of /24s and Internet bloat.   I
> realize the customer needs its address space to announce
> separately, but should we allow 			them to
> freely announce random
> /24's?   This is only due to that the customer received IPs
> growing over the years, rather than getting a single block up
> front.
> 	2)  	It seems that other providers are allowing our customers
> hijack our routing space piece 		by piece.   I will happily
> participate in multihoming a customer, but I would hope it
> involves us.  We can make a contiguous allocation from our CIDR
> blocks, and then work with 		the customer in a more consistent
> manner.  Much of this is customer education about
> multihoming,
> but unfortunately we often find out too late.
> So the question becomes, what do providers do to determine
> a block is coming from, and what is its implications on the
> global routing system?   Just cutting and pasting an email from
> the customer into an access-list seems to be what we have
> I'd be interested to hear what others thoughts and experience
> with this.  Perhaps I'm just overly concerned with a normal
> happening on the Internet.
> Comments?
> Tony

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