RE: BGP and anycast

If I understand this correctly you are trying to advertise one /24 out to 2
separate providers on the internet.
If this is the case you will need to make sure that the 2 providers in this
scenario are the same and will allow you to advertise smaller subnets of
this block. If you advertise the same block out of 2 separate regions BGP
will not know where to send traffic. BGP will select the most specific and
route to this destination. If there are 2 similar advertisements there will
be routing anomalies. If you are trying to connect the sites together [ one
subnet ] across the internet, the best way to do this is to establish a VPN
between sites and advertise the entire /24 out of one region and share the
subnet between regions over the VPN. The points of the VPN will need to be
of public address space that is either advertised or routed to you from your
provider. Netscreen has a solution for this. This will enable you to
receive traffic destined to your network at one location and forward the
necessary traffic across the internet to your other region over the VPN. I
have found it very difficult to get anyone to listen to advertisements less
than a /24 this is why I suggest that the carrier between regions be the
same it would be easier to get them to satisfy this request. I thought of
the use of IBGP but you will still experience the same issues of
reachability i.e the transit carrier would need to advertise no less than
the /24.

Hope this helps
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