RE: Confussion over multi-homing
David Lott: Thursday, September 14, 2000 10:34 AM wrote:
First, allow me to state the assumptions that I'm under. I understand the policy to state that if a business needs to multi-home and requires less space than a /20, then they should request this space from their ISP. I also understand that there are filters at the /20 boundaries in order to minimize the size of the routing table.
Question: Doesn't this break multi-homing for end users that need less than a /20?
Yep, this has been a topic here before...no real resolution. You didn't really need to prove the case, it has already been proven. The only way that you can do it is to justify a /20 or larger, get portable IP space from ARIN, and make your own peering arrangements with your upstreams. Considering that you will probably burn the best part of the /20 with distributed services, this increases your internal administration costs substantially. What you will have is a very low-density use net-block, but at least you can now multi-home and even have some geographical independence, for multiple-site use. If you have good admins, the whole thing can be folded/collapsed into about 20 physical servers, or less (Lintel boxen keep the costs low too, see: VA-Linux, about two racks). Is this wasteful of IP space? ...absolut! Is this necessary? ...sometimes. If you are building a H-Rel/Hi-Avail/Hi-Secure site(s), you ain't getting there without multi-homing with at least three providers. If you have multiple sites, you can't get there without multi-homing on an ASN that will be advertised (at least a /20, probably a /19). Do I tell clients this? ... absolut! Have I done this for clients? ... Yep, and I ain't saying who for either. --- R O E L A N D M . J . M E Y E R CEO, Morgan Hill Software Company, Inc. Managing Architect Tel: (925)373-3954 Fax: (925)373-9781 http://staff.mhsc.com/rmeyer
On Thu, 14 Sep 2000, Roeland M.J. Meyer wrote:
David Lott: Thursday, September 14, 2000 10:34 AM wrote:
First, allow me to state the assumptions that I'm under. I understand the policy to state that if a business needs to multi-home and requires less space than a /20, then they should request this space from their ISP. I also understand that there are filters at the /20 boundaries in order to minimize the size of the routing table.
Not *all* boundaries, see below.
Question: Doesn't this break multi-homing for end users that need less than a /20?
Yep, this has been a topic here before...no real resolution. You didn't really need to prove the case, it has already been proven.
No. From a post I made to this list on 6/22/2000: ++> Here's the deal. If you number out of Provider1's CIDR block ++> but advertise your more-specific to Provider2 and the two Providers ++> touch and Provider1 accepts the more-specific route from Provider2, ++> you should have no problem reaching anyone. ++> ++> Here's the reason: Everyone accepts Provider1's announcement of the block. ++> When your link to P1 is up, any traffic they recieve for your prefix ++> gets routed over that link since they carry your more-specific internally. ++> However, if other providers here the more-specific from P2, they'll ++> send directly via P2 who sends it over the link to you. ++> If your link to P1 goes down, P1 won't see the direct route to you ++> but should see the route via P2 if P1 is accepting it. (Some ++> may either block the announcement or have anti-spoofing packet filters ++> at their borders that block the traffic itself). ++> As long as Provider1 sees the more-specific from Provider2, the length is irrelevant. Does someone disagree? ++> There are many misconceptions about this topic. ++> Hopefully this explanation has helped someone. Tony
Yep, this has been a topic here before...no real resolution. You didn't really need to prove the case, it has already been proven.
No. From a post I made to this list on 6/22/2000:
++> Here's the deal. If you number out of Provider1's CIDR block ++> but advertise your more-specific to Provider2 and the two Providers ++> touch and Provider1 accepts the more-specific route from Provider2, ++> you should have no problem reaching anyone. ++> ++> Here's the reason: Everyone accepts Provider1's announcement of the block. ++> When your link to P1 is up, any traffic they recieve for your prefix ++> gets routed over that link since they carry your more-specific internally. ++> However, if other providers here the more-specific from P2, they'll ++> send directly via P2 who sends it over the link to you.
But if your chunk of space is greater than /20, the other providers will filter P2's announcement of your space and you are back to square one. Well, at least you won't be cut off from the entire Internet, I guess that's something. Square 1.5. Austin
participants (3)
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Austin Schutz -
Roeland M.J. Meyer -
Tony Tauber