As far as "may not be globally routable" is concerned, keep in mind that a
lot of the big boys use access-lists to filter smaller networks out.
There was an old standard access-list *Access-list 112* I think it was, that
used to block all bar /19s. So, if you were advertising anything smaller
than a /19, it wouldn't be seen by anyone using that access-list (eg /20,
/21 etc). There's a new standard one - access-list 190 which we use albeit
a little edited (http://www.magna.com.au/~phillipg/acl190.txt) that denies
anything smaller than a /24 (eg /25, /26 etc). So, that's another example
of why anything less than a /24 will generally not be guaranteed as globally
routable.
Cheers,
Em
-----Original Message-----
From: Jason [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, August 29, 2000 2:32 PM
To: [EMAIL PROTECTED]
Subject: Re: Minimum BGP Address Aggregation
""Howard C. Berkowitz"" <[EMAIL PROTECTED]> wrote in message
news:v04220882b5d05ad06a2b@[63.216.127.98]...
> >What do you mean by "may NOT be globally routable" ? This would be due to
> >the address aggregation on the the 1st Tier ISP ? Would this be a
problem
> >even if I'm connected to a 1st Tier ISP rather than a lower Tier ISP ?
>
> Depends on the policy of the particular ISP, even tier 1. Some
> simply don't want to advertise any /24 that's not part of their
> address space, some won't do it except for direct customers who have
> negotiated to advertise provider-independent address space, some
> might not be willing to negotiate to advertise an a more-specific
> assignment of another provider's space, and some don't care.
So this is a policy issue where the ISP doesn't want to advertise the
address rather than that it cannot be done ? Is there a specific range of
address defined as "provider-independant address space" and if so, who do we
need to get hold of to get this addresses ?
> > Could I multihome a network
> >across different countries or different geographical region ?
>
> You might -- which might or might not be a good idea. Depends what
> you are trying to accomplish. When I've done this, there were some
> very carefully designed policies to protect transoceanic bandwidth.
In this scenerio, I want to allow users to access this network without being
affected by the congestions that occurs between international link. I have
simulated the network links and policies in the lab to protect this
bandwidth but would like to draw further feedback to identify any other
potential problem. It is also one of the more interesting BGP exercises .
> >How could I ensure that the traffic takes the nearest route to the
network
> >and the data traffic from the network takes the nearest gateway out to
the
> >destination on the internet ? What is the potential problem with this ?
>
> Not sure what you mean by this. In general, the default of most
> routing schemes is closest exit (hot potato) rather than best exit
> (cold potato). Again, discussed in some detail in the new paper.
Iin this case, since the gateways are transoceanic, without redistributing
BGP into IGP, it would appear that it is difficult to select the best exit
using IGP.
Jason
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