I've heard that most ISPs will filter less than /19. If this is true, then
only the ISP who owns the aggregate route will get heard by most other ISPs.
Can anyone confirm at which point most ISPs filter? I know at a minimum
most won't accept more specific than /24.
I finally got some evil internal routing & vpn issues taken care of, and
should be finally implementing BGP with Sprint & UUNET (geeze, it's been
forever dealing with these internal issues). If nothing else, I'll ask
their BGP folks what they filter at.
I can also confirm that about double the ASN's in use (9731) have been
handed out. We were given ASN 18506 in September.
--
Jason Roysdon, CCNP+Security/CCDP, MCSE, CNA, Network+, A+
List email: [EMAIL PROTECTED]
Homepage: http://jason.artoo.net/
Cisco resources: http://r2cisco.artoo.net/
""Howard C. Berkowitz"" <[EMAIL PROTECTED]> wrote in message
news:p05001919b68e6e6b973a@[63.216.127.98]...
> >Brian,
> >
> >Hi! Funny you bring this up, I just got a phone call on it today.
> >Basically, you can have two seperate ISPs and have incoming redundant
> >connections without using BGP. ISP1 will provide a block of IPs from a
> >portion of their CIDR block to the "company." Since this is part of
ISP1s
> >CIDR block, they already broadcast a route to the rest of the internet
> >containing the company's block of IPs.
>
>
> >
> >ISP2 will then also broadcast a route to ISP1's block of IPs (just the
> >block!!!). The tricky part comes when you try to do load balancing
between
> >the two for incoming traffic!!!
> >
> > I am making several assumptions here (that the ISPs will play nice with
> >each other among other things).
> >
> ISP1, however, MUST advertise not its aggregate alone, but both its
> aggregate and the more-specific customer block that also is
> advertised by ISP2.
>
> Assume the following:
>
> ISP1 has the block 192.168.0.0/16. This is the only block it advertises.
>
> It delegates 192.168.2.0/24 to the customer.
>
> ISP2 advertises 192.168.2.0/24.
>
> So in the global routing table, there will be two routes:
>
> 192.168.0.0/16 ISP1
> 192.168.2.0/24 ISP2
>
> Since 192.16.2.0/24 is more specific than 192.168.0.0/16, the rest of
> the world will send ALL 192.168.2.0/24 traffic to ISP2.
>
> By having ISP1 advertise both its aggregate and the more-specific,
> the routing system conceptually will contain:
>
> 192.168.0.0/16 ISP1
> 192.168.2.0/24 ISP1
> 192.168.2.0/24 ISP2
>
> Other AS will install the ISP1 route to 192.168.2.0/24 if their
> connectivity to ISP1 is better than their connectivity to ISP2, and
> vice versa.
>
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