From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Tue Aug 09 2005 - 19:11:31 GMT-3
At 4:04 PM -0400 8/9/05, Brian McGahan wrote:
> There are different types of IPv4 address assignments.
>Provider-based addressing is when you get an IPv4 block assigned from
>your specific ISP. Typically BGP is not required in cases like this
>since you do not need to announce the ISPs address space back to them.
>With this design if you change providers you must change addressing.
>
> Other address blocks are known as "portable" addresses or
>"provider independent" addresses. These blocks assigned to your network
>directly through agencies such as ARIN or APNIC. This address space is
>then announced to your provider(s) via BGP. Since you "own" this
>address space you ultimately determine how it is routed throughout the
>network.
>
> The reason why I said that "Most ISPs will not allow you to
>announce another ISPs address space." has to do with how peering and
>transit agreements are setup. For example suppose you have links to ISP
>A and ISP B, but your address space belongs to ISP A. By announcing ISP
>A's address space to ISP B, ISP B is providing transit to ISP A (which
>is essentially you) free of charge. Policies will vary from provider to
>provider but typically the bigger the ISP is the more strict their
>policies will be.
In multihoming with PA space, the key is that the customer AS only
announces their more-specific delegated space to other providers.
Yes, it is operational practice that the second (or further) provider
will check with the provider that "owns" the address space before
advertising it.
Let AS 6666 be a customer of AS1 and AS2.'
Assume AS1 has 1.0.0.0/8 and AS2 has 2.0.0.0/8. Both advertise these
to the world.
AS1 delegates 1.254.255.0/24 to AS 6666.
To multihome, AS6666 advertises _only_ the more-specific
1.254.255.0/24 prefix in 1.0.0.0/8 to AS2.
Assume that AS6666 is the only multihomed customer of AS2. Remember,
AS6666 started out with its address space being part of AS1's /8, so
the world can reach AS6666 through AS1. For AS6666, as well as AS2's
customers with PA space, AS2 must announce: (2.0.0.0/8,
1.254.255.0/24). Now the world can reach AS6666 from AS2.
We aren't finished. Once AS2 announces 1.254.255.0/24, that
advertisement will be more specific than 1.0.0.0/8. Unless other
measures are taken, all the traffic to AS6666 will go through AS2,
unless AS2 stops advertising it. This would be a pure backup case,
and not very likely.
For everything to work in a multihomed setup, AS1 can't just
advertise its aggregate, but must advertise (1.0.0.0/8,
1.254.255.0/24) for the load to spread between the two providers.
>
> Check here for more info:
>
>http://www.apnic.net/meetings/12/docs/proposal-multihome-assign.html
>
>http://www.ripe.net/ripe/meetings/ripe-39/presentations/aspolicy/
>
>
>HTH,
>
>Brian McGahan, CCIE #8593
>bmcgahan@internetworkexpert.com
>
>Internetwork Expert, Inc.
>http://www.InternetworkExpert.com
>Toll Free: 877-224-8987 x 705
>Outside US: 775-826-4344 x 705
>24/7 Support: http://forum.internetworkexpert.com
>Live Chat: http://www.internetworkexpert.com/chat/
>
>
>> -----Original Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
>Of
>> Vazman
>> Sent: Tuesday, August 09, 2005 10:56 AM
>> To: Jens Petter Eikeland
>> Cc: Helena Qiu; ccielab@groupstudy.com
>> Subject: Re: is it possible to use private AS# peering with 2 ISPs?
>>
>> Brian,
>>
>> In reference to your statement.
>>
>> "Most ISPs will not allow you to announce another ISPs address space."
>>
>> How would you go about setting up Internet connectivity with 2
>> different ISP's (for diversity) and use the same address space? Just
>> curious.
>>
>> Thanks.
>>
>> On 8/9/05, Jens Petter Eikeland <jenseike@start.no> wrote:
>> > Hi ,
>> >
>> > The isp will filter out that privat as, so you should be good
>> >
>> > Jens Petter Eikeland
>> >
>> > -----Opprinnelig melding-----
>> > Fra: nobody@groupstudy.com [mailto:nobody@groupstudy.com] Pe vegne
>av
>> Helena
>> > Qiu
>> > Sendt: 9. august 2005 16:58
> > > Til: ccielab@groupstudy.com
>> > Emne: is it possible to use private AS# peering with 2 ISPs?
>> >
>> > Dear all,
>> >
>> > We are using ISP A's service. ISP A assigned ip range and private AS
>> number
>> > to us. For the backup purpose, we are going to use ISP B as well. We
>are
>> > going to keep our IP range and private AS # assigned by ISP A. Is it
>> > possible for us to use this private AS# to peer with ISP B?
>> >
>> > Please advise. Thanks.
>> >
>> > __________________________________________________
>> > Do You Yahoo!?
>> > Tired of spam? Yahoo! Mail has the best spam protection around
>> > http://mail.yahoo.com
>> >
>> >
>_______________________________________________________________________
>> > Subscription information may be found at:
>> > http://www.groupstudy.com/list/CCIELab.html
>> >
>> >
>_______________________________________________________________________
>> > Subscription information may be found at:
>> > http://www.groupstudy.com/list/CCIELab.html
>>
>>
>_______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
>_______________________________________________________________________
>Subscription information may be found at:
>http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sun Sep 04 2005 - 17:01:18 GMT-3