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I have a customer who currently has a 2600 series router with a T1 to the
Internet. They get their external IP space from a small local ISP. They
have a small IP block (/29 mask). This customer wants to have redundant and
load balancing Internet lines. I contacted their existing ISP to enquire if
they supported BGP with the specifications that the customer AS no be used
as a transit AS and that I wanted to receive default routes only.

The ISP is stating that they cannot support BGP due to restrictions of the
size of the IP block. Is a /29 too small for BGP? Is this a legitimate
restriction of the ISP?

"SP" <> wrote in message news:jxCqb.357$jt.305@okepread05...
> I have a customer who currently has a 2600 series router with a T1 to the
> Internet. They get their external IP space from a small local ISP. They
> have a small IP block (/29 mask). This customer wants to have redundant
and
> load balancing Internet lines. I contacted their existing ISP to enquire
if
> they supported BGP with the specifications that the customer AS no be used
> as a transit AS and that I wanted to receive default routes only.
>
> The ISP is stating that they cannot support BGP due to restrictions of the
> size of the IP block. Is a /29 too small for BGP? Is this a legitimate
> restriction of the ISP?
>

Technically, no. Practicaly Yes. It's kind of a hard to get ASN for such a
small block...

Ivan

On Thu, 6 Nov 2003 19:26:02 -0600, "SP" <> wrote:

>I have a customer who currently has a 2600 series router with a T1 to the
>Internet. They get their external IP space from a small local ISP. They
>have a small IP block (/29 mask). This customer wants to have redundant and
>load balancing Internet lines. I contacted their existing ISP to enquire if
>they supported BGP with the specifications that the customer AS no be used
>as a transit AS and that I wanted to receive default routes only.
>
>The ISP is stating that they cannot support BGP due to restrictions of the
>size of the IP block. Is a /29 too small for BGP? Is this a legitimate
>restriction of the ISP?

Generally the smallest prefix size that is accepted in the global BGP
routing tables is a /24.

The desire to multihome, however, is usually sufficient justification
to get a /24 from an ISP, and is always sufficient justification to
get an AS from ARIN. (I assume other RIRs have the same policy on
this.)

-Terry

Terry Baranski <0VE> writes:
>
> Generally the smallest prefix size that is accepted in the global BGP
> routing tables is a /24.

If it comes from the swamp or other PI allocation space. From well known
RIR blocks that are typically allocated as /19s, /20s or /21s, it seems
to be common practice that only announcements matching these allocation
sizes are accepted, to prevent those who try to load balance by announcing
their allocation in parts from sucking up others resources.

> The desire to multihome, however, is usually sufficient justification
> to get a /24 from an ISP, and is always sufficient justification to
> get an AS from ARIN. (I assume other RIRs have the same policy on
> this.)

ASN-wise yes. But just the desire to multihome doesn't justify a /24 in
RIPE area. A /24 (or shorter) is assigned only if there is well documented
need for that amount of addresses (and "I need them for no other reason
but to get global routing" doesn't count).

--
The _S_anta _C_laus _O_peration
or "how to turn a complete illusion into a neverending money source"

-> Andre "ABPSoft" Beck +++ ABP-RIPE +++ Dresden, Germany, Spacetime <-

On 12 Nov 2003 20:21:31 +0100, Andre Beck <> wrote:

>Terry Baranski <0VE> writes:
>>
>> Generally the smallest prefix size that is accepted in the global BGP
>> routing tables is a /24.
>
>If it comes from the swamp or other PI allocation space. From well known
>RIR blocks that are typically allocated as /19s, /20s or /21s, it seems
>to be common practice that only announcements matching these allocation
>sizes are accepted, to prevent those who try to load balance by announcing
>their allocation in parts from sucking up others resources.

There's still some question as to just how common that is. Verio is
the only Tier-1 I know of that does it. Routing table growth seems to
be less of a concern these days relative to a few years ago when it
was exponential.

>> The desire to multihome, however, is usually sufficient justification
>> to get a /24 from an ISP, and is always sufficient justification to
>> get an AS from ARIN. (I assume other RIRs have the same policy on
>> this.)
>
>ASN-wise yes. But just the desire to multihome doesn't justify a /24 in
>RIPE area. A /24 (or shorter) is assigned only if there is well documented
>need for that amount of addresses (and "I need them for no other reason
>but to get global routing" doesn't count).

I was referring to PA space. Are you saying that a multihomer can't
get a PA /24 from an ISP who gets its IP space from RIPE?

-Terry

On Thu, 13 Nov 2003 20:57:39 -0500, Terry Baranski
<0VE> wrote:

> Routing table growth seems to
>be less of a concern these days relative to a few years ago when it
>was exponential.

Not exponential... Wrong word. I think the word I was looking for was
"a lot higher than it is now." 2000 was a bad year for routing table
growth but the rate has decreased substantially since then. This,
along with cheaper memory prices and faster hardware overall, may
cause providers like Verio to rethink their BGP filtering strategies.

-Terry

Terry Baranski <0VE> writes:
> On 12 Nov 2003 20:21:31 +0100, Andre Beck <> wrote:
>
> >Terry Baranski <0VE> writes:
> >>
> >> Generally the smallest prefix size that is accepted in the global BGP
> >> routing tables is a /24.
> >
> >If it comes from the swamp or other PI allocation space. From well known
> >RIR blocks that are typically allocated as /19s, /20s or /21s, it seems
> >to be common practice that only announcements matching these allocation
> >sizes are accepted, to prevent those who try to load balance by announcing
> >their allocation in parts from sucking up others resources.
>
> There's still some question as to just how common that is. Verio is
> the only Tier-1 I know of that does it. Routing table growth seems to
> be less of a concern these days relative to a few years ago when it
> was exponential.

There was a very popular Cisco platform (the 720x with NPE200) that would
still serve a number of ISPs well if it just could deal with todays DFZ.
But you cannot plug more than 128MiB into these blades and so you cannot
plug them into the DFZ with CEF enabled and full tables. Luckily folks
found out the NPE225 could eat more SDRAM than was initially specified...

> >> The desire to multihome, however, is usually sufficient justification
> >> to get a /24 from an ISP, and is always sufficient justification to
> >> get an AS from ARIN. (I assume other RIRs have the same policy on
> >> this.)
> >
> >ASN-wise yes. But just the desire to multihome doesn't justify a /24 in
> >RIPE area. A /24 (or shorter) is assigned only if there is well documented
> >need for that amount of addresses (and "I need them for no other reason
> >but to get global routing" doesn't count).
>
> I was referring to PA space. Are you saying that a multihomer can't
> get a PA /24 from an ISP who gets its IP space from RIPE?

Not if he has no other reasonable justification for beeing assigned a /24
and the ISP refuses to support a lie. This is independent of PA or PI.
The potential multihomer could also try to become a LIR and just use
part of the allocation he gets for his own assignment. The RIPE, however,
requires an initial need for 25% of the space and a projected need of 50%
IIRC - so no, you cannot become a LIR and get a /21 to announce and then
just use one /27 out of that, either. That is harsh, but it is the price
of conservation, especially outside the US. And it's rather more politics
than tech. Beeing able to pace the growth of the global table by making
it harder to become BGP multihomed for non-ISPs with very small address
ranges seems to be an accepted side effect of the conversation rules.

--
The _S_anta _C_laus _O_peration
or "how to turn a complete illusion into a neverending money source"

-> Andre "ABPSoft" Beck +++ ABP-RIPE +++ Dresden, Germany, Spacetime <-

Terry Baranski <0VE> writes:
> On Thu, 13 Nov 2003 20:57:39 -0500, Terry Baranski
> <0VE> wrote:
>
> > Routing table growth seems to
> >be less of a concern these days relative to a few years ago when it
> >was exponential.
>
> Not exponential... Wrong word.

Well, at the climax of .com, it really looked like it would grew expo-
nential. Until the bubble blew up...

> I think the word I was looking for was
> "a lot higher than it is now." 2000 was a bad year for routing table
> growth but the rate has decreased substantially since then. This,

When .com turned into .gone, the table took a hickup and settled for
a while. Since late 2002, it seems to be constantly growing again, and
speed slowly increases again, too. It's just about to exceed 128Ki
routes (bye bye 128Ki CAMs)...

> along with cheaper memory prices and faster hardware overall, may
> cause providers like Verio to rethink their BGP filtering strategies.

IMO this never was a problem of memory prices. It was a problem of
having to replace a complete chassis just to upgrade to some silly
256MiB. For gods sake some kind soul found out the NPE225 (which is
the best NPE that still runs in a non-VXR 720x) can actually digest
a straight CL2 256MiB DIMM. With .gone still depressing on us and the
overcapacity deployed before that, there is likely some pause in the
swapout of old equipment. So at the moment, I don't really expect
filter policies to change soon.

--
The _S_anta _C_laus _O_peration
or "how to turn a complete illusion into a neverending money source"

-> Andre "ABPSoft" Beck +++ ABP-RIPE +++ Dresden, Germany, Spacetime <-