I'm sure I can't be the only one that notices the BGP inconsistancies in their route tables.... Seeing the latest NZRR update prompted me to check the BGP tables again... We do not and will not accept route advertisements containing private AS numbers from our peers. The reason we don't is the same reason we don't route RFC1918 space externally... If a customer has their own address space and wants to multi-home, they should also have their own AS. Advertising up private AS numbers that should really remain within the network isn't a solution. Inconsistant AS-paths are bad enough, without creating additional problems... At least we're only seeing 5 class C's being advertised at the APE with inconsistant AS-paths at the moment. Perhaps BGP routing could be a topic for discussion at NZNOG 2005? Cheers, Gordon
Gordon Smith wrote:
I'm sure I can't be the only one that notices the BGP inconsistancies in their route tables....
Seeing the latest NZRR update prompted me to check the BGP tables again... We do not and will not accept route advertisements containing private AS numbers from our peers. The reason we don't is the same reason we don't route RFC1918 space externally...
The private AS number Gordon saw is for someone who peers with the WIX route servers. We use private ASes extensively on the WIX but you shouldn't see private AS numbers from the APE or WIX route servers. They're removed from any adverts from AS9560 or AS9439 respectively.
If a customer has their own address space and wants to multi-home, they should also have their own AS. Advertising up private AS numbers that should really remain within the network isn't a solution. Inconsistant AS-paths are bad enough, without creating additional problems...
Many of the small players on the WIX aren't multi-homing. They're simply peering with the WIX route servers to accelerate their content transfers across the exchange and/or avoid traffic charges from their ISP who in some cases route their traffic via Auckland or worse. If/when they decide to have a BGP session with their ISP they get steered firmly by us into a public AS.
At least we're only seeing 5 class C's being advertised at the APE with inconsistant AS-paths at the moment. Perhaps BGP routing could be a topic for discussion at NZNOG 2005?
I'd be keen to know about these - OOB would be good.
Cheers, Gordon
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Hi Gordon, Gordon Smith said the following on 19/01/2005 10:16:
Seeing the latest NZRR update prompted me to check the BGP tables again... We do not and will not accept route advertisements containing private AS numbers from our peers. The reason we don't is the same reason we don't route RFC1918 space externally...
:-)
If a customer has their own address space and wants to multi-home, they should also have their own AS. Advertising up private AS numbers that should really remain within the network isn't a solution. Inconsistant AS-paths are bad enough, without creating additional problems...
Why are inconsistent AS-paths bad? Operationally, I mean. (I hadn't had any operational mishaps in all my years at UUNET because of inconsistent AS-paths, so I'm wondering if something else causes an issue now?) Technically there is nothing wrong with them. As you observed, it's simply an organisation multihoming using a private ASN - hopefully their upstreams are stripping out the private ASN before they propogate the originated prefixes further. (Mind you, I find it rare for two ISPs to agree which private ASN to use for a mutual customer to multihome - often so much easier to obtain a real one.) And yes, people can quite easily use public ASNs. It's simply a case of an APNIC member obtaining an ASN so their customer can multihome. And that can't be too hard, right? philip --
participants (3)
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Andy Linton -
Gordon Smith -
Philip Smith