Fwd: Re: Re: What is the most standard subnet length on internet

Howard C. Berkowitz hcb at netcases.net
Fri Dec 19 09:36:27 CST 2008


I may not completely understand your concerns, especially about customers
moving. I would, however, strongly encouraging not using the terms A,B or
C in NANOG discussions; I've found they lead to assumptions based on
obsolete ideas.

Let's assume an enterprise has had one transit provider, who is in the
default-free zone.  Working together, the customer and provider agreed the
customer needed a /23, and the provider assigns 1.0.0.0/23 as a PA subpart
of its own space. 1.0.0.0/8. Using RFC 1998 techniques, for load sharing
at four POPs of that same provider, that customer then announces, at each
POP, a /25 reflecting the /25 used for machines in the local area of that
POP, but also announces the /23. With a single provider, the RFC1998
method applies, and the routes announced are tagged with NO-EXPORT.  As
long as the enterprise is not multihomed, its more-specifics will be
handled properly by provider A's announcement of 1.0.0.0/8?

Now, assume that customer gets a single link to a different provider B,
whose PI space is 2.0.0.0/8. For multihoming to work, at least two things
start to happen. Both providers A and B need to announce 1.0.0.0/23 to the
rest of the Internet. If only provider B advertised (2.0.0.0/8,
1.0.0.0/23) to the rest of the internet, all traffic to the enterprise
would come through provider B, because it announces a more-specific. For
the traffic to work, BOTH A and B have to announce 1.0.0.0/23, so other
providers, with full routes, spread load to the two providers.

The enterprise can still announce both /23 and /25 to Provider A, with
NO-EXPORT on the /25's, because Provider A can make use of the /25 to
better manage traffic to its POPs.  Administratively, Providers A and B
have to agree to Provider B advertising a piece of Provider A's space.

Am I answering the question you are asking?


Á¤Ä¡¿µ wrote:
> "You have to change your server's IP address if you want move your server
> to other place"
>
>  -> It is very natural case, but some customer could think of it will be
> okey to move if they have C class.
> but I have different idea. because the border router of that center is
> annoucing more greater IP block,
> and if customer move to other center with C class, then I have to newly
> announce that C class at the border router of other center.
> and then it is the time my hierachy structure is broken.
> To prevent this situation, I'm trying to find some standard material every
> person would understand and accept.
>
> =============================================
>  Chi-Young Joung
>  SAMSUNG NETWORKS Inc.
>  Email: lionair at samsung.com
>  Tel +82 70 7015 0623, Mobile +82 17 520 9193
>  Fax +82 70 7016 0031
> =============================================
>
> ------- Original Message -------
> Sender : Á¤Ä¡¿µ<lionair at samsung.com>  °úÀå/±â¼ú1ÆÀ/»ï¼º³×Æ®¿÷½º
> Date   : 2008-12-19 13:43 (GMT+09:00)
> Title  : Re: Re: What is the most standard subnet length on internet
>
> Suresh,
>
> Yes, I guess my concern is close to the second meaning.
>
> It seems so simple. Currently annoucement of /24 seems to be okey, most
> upstream providers accept this.
> However I wonder if there is any ground rule based on any standard or
> official recommandation.
> If there is some standardized rule about prefix length to be annouced, I
> will make my bgp & IP allocation policy of
> each data center of my company, and I will be able to more fairly and
> squarely speak to my customer like this
> "You have to change your server's IP address if you want move your server
> to other place"
>
> chiyoung
> =============================================
>  Chi-Young Joung
>  SAMSUNG NETWORKS Inc.
>  Email: lionair at samsung.com
>  Tel +82 70 7015 0623, Mobile +82 17 520 9193
>  Fax +82 70 7016 0031
> =============================================
>
> ------- Original Message -------
> Sender : Suresh Ramasubramanian<ops.lists at gmail.com>
> Date   : 2008-12-19 12:37 (GMT+09:00)
> Title  : Re: What is the most standard subnet length on internet
>
> Chi Young, let me clarify one thing here ..
>
> Do you mean IP allocation as in subnet allocation, swipping in apnic
> or through a rwhois server etc?
>
> Or do you mean "what is the minimum subnet size I can announce on the
> internet and have other providers not drop it on the floor"?
>
> srs
>
> On Fri, Dec 19, 2008 at 8:10 AM, Á¤Ä¡¿µ <lionair at samsung.com> wrote:
>> Hi everyone,
>>
>> I'm going to rebuild IP allocation policy of my company and I am looking
>> for some standard reference for my policy.
>> I have already studied some standard like RFC1518, RIPE181, RFC2050 and
>> I got it is very important to maintain hierachy structure.
>> However, what I am really wondering is what is the most standard subnet
>> length that always can be guaranteed through Internet. less than /24 bit
>> ?
>> I could not find any documents about that, which subnet length is most
>> proper value and pursue internet standard policy ?
>>
>
>
>
>
>





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