Re: all the mails on Filtering
Hi, So what happens to multihoming assignments made by the ISP? That means the multihoming assignment can't be used as a backup. If the customer's connection to the ISP which made the multihoming assignment gets lost, then it can't use its multihoming assignments (say a /24) to get traffic from some other ISP?! Thanks to all, Harsha. On Wed, 13 Nov 2002, Buddy Bagga wrote:
Greets,
Look at <http://www.nanog.org/filter.html>. If I remember correctly, Verio used to filter prefixes longer than /19s in classful A range. Apparently this isn't the case anymore. But it would be naive to think that ISP only filter prefixes longer than /24.
Cheers,
On Wed, 13 Nov 2002, Harsha Narayan wrote:
Are there some ISPs who filter prefixes longer than /19 or a /20?. I thought they filtered only prefixes which are longer than /24?
~ Buddy Bagga Genuity | BBN
If you're multihomed you can generally obtain provider indepdent space from your RIR. Most people who do this filtering do it on the RIR boundaries for their minimum allocation. If you are annoucing your provider assigned space as a /24, they tend to announce the (/14 - /rir-minimum) so your packets will follow the aggregate. If they are not announcing their aggregate then you will have problems. Most people in that case would blame the provider for not announcing their space. - Jared On Wed, Nov 13, 2002 at 10:25:53AM -0800, Harsha Narayan wrote:
Hi,
So what happens to multihoming assignments made by the ISP? That means the multihoming assignment can't be used as a backup. If the customer's connection to the ISP which made the multihoming assignment gets lost, then it can't use its multihoming assignments (say a /24) to get traffic from some other ISP?!
Thanks to all, Harsha.
On Wed, 13 Nov 2002, Buddy Bagga wrote:
Greets,
Look at <http://www.nanog.org/filter.html>. If I remember correctly, Verio used to filter prefixes longer than /19s in classful A range. Apparently this isn't the case anymore. But it would be naive to think that ISP only filter prefixes longer than /24.
Cheers,
On Wed, 13 Nov 2002, Harsha Narayan wrote:
Are there some ISPs who filter prefixes longer than /19 or a /20?. I thought they filtered only prefixes which are longer than /24?
~ Buddy Bagga Genuity | BBN
-- Jared Mauch | pgp key available via finger from jared@puck.nether.net clue++; | http://puck.nether.net/~jared/ My statements are only mine.
Hi, But it appears that there are many cases where customers prefer to take a prefix from the ISP rather than an RIR even if it is a /19 or a /20 - for example from the /11 of a big ISP, there are 50 /19s and /20s which are multihoming assignments. I was told that this saves the cost of RIR membership for the customer. Moreover, how do we know the RIR makes multihoming assignments from a separate /8 - atleast in the case of RIPE it does not I think (in the case of APNIC it does). If we are of sure of this - i.e. that a multihoming assignment from an RIR comes from a separate section of the address space - we can't filter. Harsha. On Wed, 13 Nov 2002, Jared Mauch wrote:
If you're multihomed you can generally obtain provider indepdent space from your RIR.
Most people who do this filtering do it on the RIR boundaries for their minimum allocation.
If you are annoucing your provider assigned space as a /24, they tend to announce the (/14 - /rir-minimum) so your packets will follow the aggregate. If they are not announcing their aggregate then you will have problems. Most people in that case would blame the provider for not announcing their space.
- Jared
On Wed, Nov 13, 2002 at 10:25:53AM -0800, Harsha Narayan wrote:
Hi,
So what happens to multihoming assignments made by the ISP? That means the multihoming assignment can't be used as a backup. If the customer's connection to the ISP which made the multihoming assignment gets lost, then it can't use its multihoming assignments (say a /24) to get traffic from some other ISP?!
Thanks to all, Harsha.
On Wed, 13 Nov 2002, Buddy Bagga wrote:
Greets,
Look at <http://www.nanog.org/filter.html>. If I remember correctly, Verio used to filter prefixes longer than /19s in classful A range. Apparently this isn't the case anymore. But it would be naive to think that ISP only filter prefixes longer than /24.
Cheers,
On Wed, 13 Nov 2002, Harsha Narayan wrote:
Are there some ISPs who filter prefixes longer than /19 or a /20?. I thought they filtered only prefixes which are longer than /24?
~ Buddy Bagga Genuity | BBN
-- Jared Mauch | pgp key available via finger from jared@puck.nether.net clue++; | http://puck.nether.net/~jared/ My statements are only mine.
Hi Harsha, this occurs quite often as a topic for discussion here.. the answer is they do it because they can and unless you have an RIR allocation theres no guarantees and to be fair the RIRs do state that. and good/bad agree/disagree some ISPs filter more than others and theres not a lot you can do! providing you connect to the provider who gave you the prefix you wont have any issues.... Steve On Wed, 13 Nov 2002, Harsha Narayan wrote:
Hi, But it appears that there are many cases where customers prefer to take a prefix from the ISP rather than an RIR even if it is a /19 or a /20 - for example from the /11 of a big ISP, there are 50 /19s and /20s which are multihoming assignments.
I was told that this saves the cost of RIR membership for the customer.
Moreover, how do we know the RIR makes multihoming assignments from a separate /8 - atleast in the case of RIPE it does not I think (in the case of APNIC it does). If we are of sure of this - i.e. that a multihoming assignment from an RIR comes from a separate section of the address space - we can't filter.
Harsha. On Wed, 13 Nov 2002, Jared Mauch wrote:
If you're multihomed you can generally obtain provider indepdent space from your RIR.
Most people who do this filtering do it on the RIR boundaries for their minimum allocation.
If you are annoucing your provider assigned space as a /24, they tend to announce the (/14 - /rir-minimum) so your packets will follow the aggregate. If they are not announcing their aggregate then you will have problems. Most people in that case would blame the provider for not announcing their space.
- Jared
On Wed, Nov 13, 2002 at 10:25:53AM -0800, Harsha Narayan wrote:
Hi,
So what happens to multihoming assignments made by the ISP? That means the multihoming assignment can't be used as a backup. If the customer's connection to the ISP which made the multihoming assignment gets lost, then it can't use its multihoming assignments (say a /24) to get traffic from some other ISP?!
Thanks to all, Harsha.
On Wed, 13 Nov 2002, Buddy Bagga wrote:
Greets,
Look at <http://www.nanog.org/filter.html>. If I remember correctly, Verio used to filter prefixes longer than /19s in classful A range. Apparently this isn't the case anymore. But it would be naive to think that ISP only filter prefixes longer than /24.
Cheers,
On Wed, 13 Nov 2002, Harsha Narayan wrote:
Are there some ISPs who filter prefixes longer than /19 or a /20?. I thought they filtered only prefixes which are longer than /24?
~ Buddy Bagga Genuity | BBN
-- Jared Mauch | pgp key available via finger from jared@puck.nether.net clue++; | http://puck.nether.net/~jared/ My statements are only mine.
So what happens to multihoming assignments made by the ISP? That means the multihoming assignment can't be used as a backup. If the customer's This has been rehashed time and time again on this list, and others. The fact is, ISPs have to filter somewhere to keep routing table growth in check. It makes more sense to filter out announcements longer than
On Wed, 2002-11-13 at 13:25, Harsha Narayan wrote: the longest assignment within an RIR's space than to filter on any arbitrary boundary. I think everyone will agree with that, even if they do not agree that filtering is necessary or good. As an example of why filtering is good, click on this link and visit the CIDR Report AS Summary for an ISP here in Kentucky. They used to have over 50 useless announcements within one /18, for which they had an aggregate announced as well. They seem to have gone to some efforts to reduce the route table pollution the emit, and I applaud their efforts, however you can further reduce the amount of pollution you accept from them, and other ISPs who mistakenly announce from their IGP or for any other reason do not announce blocks as they are assigned by the RIR, simply by filtering on the minimum assignment size. http://bgp.potaroo.net/cgi-bin/as-report?as=11979&view=4637 I think there are very few networks who purposely announce longer networks to control their inbound traffic flow, verses the number who mistakenly do so. Again, everyone will agree. Except, perhaps, Ralph Doncaster. And if you want to spend your FIB entries, and your money, making your bits flow to him in the manner that's most cost-effective for ISTOP, then more power to you. Most folks will agree that is up to Ralph and Ralph's ISP(s) to work out, though. -- Jeff S Wheeler <jsw@five-elements.com>
participants (4)
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Harsha Narayan -
Jared Mauch -
Jeff S Wheeler -
Stephen J. Wilcox