[BBLISA] Telecommunications Recommendations...

[Robert Keyes]

On Thu, 15 Jul 2010, Bill Bogstad wrote:

> On Thu, Jul 15, 2010 at 6:15 PM, Robert Keyes <bob at sinister.com> wrote:
>> On Wed, 14 Jul 2010, Bill Bogstad wrote:
>>> While the above is technically correct, in his circumstance BGP is not
>>> an option.   To do BGP you TYPICALLY need to
>>> own your IP address space in order to be able to advertise them
>>> successfully.  He's talking about how many addresses his provider is
>>> going to give him so he doesn't have such addresses.
>> Not really. You can get a chunk of IP space from your main provider, and
>> advertise a route to it through your backup provider. This is becoming more
>> common as IPv4 space is becoming a more expensive commodity.
> In the past, providers would refuse to do this.  Maybe it's changed.

It's preety much become neccessary in these days where there's lots of 
routes and not enough IP space. In the case I mention, the primary ISP 
doesn't have to announce a specific route; it's aggregated in with the 
rest of their IP space. Only the secondary ISP does, so one route 
announcement is saved. I've heard cases where the customer is allowed to 
take the IP space allocated to them by the ISP even when they stop being a 
customer. At this point, there is no longer any saving of routes, so I can 
only see this being done in unusual circumstances. I imagine that the 
customer would still have to pay some fee to their original ISP for the IP 
space.

In any case, the customer is going to need their own ASN (Autonomous 
System Number). These were originally 16 bits but they're running out of 
ASNs so there is an expansion to 32 bits underway. The charge from ARIN is 
$500 and then $50 per year.

What's really interesting is how well BGP can work even when there is an 
accident and two networks accidently use the same ASN. The result is that 
the networks in question can't talk to each other, but everyone else can 
talk to either of them. If the networks are small and don't have any 
interaction, this can go unnoticed for some time. It could also be done on 
purpose, with two networks sharing the same ASN, and having a private 
route between each of their networks. I thought I was going to have to do 
this for a while (because of an ASN shortage), but ended up not having to 
(got another ASN).

>>> Second, the address space he's talking about is so small that even if
>>> he does get addresses and providers who will do BGP, no one else will
>>> pay attention to his advertisements anyway.
>> Yes, this is true, you generally need a /24 (a.k.a. class C, 255 IP
>> addresses) in order to be sure your route is propagated across the whole
>> net. But I am a bit unusure of this, there may be ways around this problem.
>>> Each advertisement takes
>>> up expensive memory in core Internet routers and the larger network
>>> providers aren't going to spend lots of money so he can have redundant
>>> network providers.  Don't go there.
>> Well yes it does take up more memory, but that doesn't mean the route won't
>> propagate through BGP. I still regularly get route announcements for very
>> small allocations (as small as a single host!), and people won't announce or
>> propagate such routes if they didn't have value.
> If you are "very important" networks will allow smaller allocations
> through. I think some of the DNS root servers are using "anycast" and
> small BGP announcements for redundancy purposes.

Anycast! Yes I hadn't thought of that..it makes sense. Well, that's the 
first new thing I've learned today.

> I still think this is likely to be a non-starter for someone in the
> original poster's situation.
> However, if he wants to pursue it; he could go look at the archives
> for the NANOG mailing list for what is typical practices on BGP
> announcements.

Indeed. Like I said, we've wandered off the original topic.

-Bob