High-availability BGP with BIRD

[Thomas Johnson]

Please let me know if bird-users is not the appropriate place for this
post; admittedly it is more of a "best practices" question...

I am in the process of trying to develop a plan for deploying BGP in a
high-availability configuration, using a pair of FreeBSD hosts running
BIRD. A number of questions have come up, leaving me unsure how to
proceed. The fact that this is my first experience with BGP doesn't
help matters. The following diagram outlines how I envision the
[physical] configuration.

                  +----------+
           +------+ router-a +-------+
    xxxxxxxx      +----------+       |
   xx      xx                     +--+-----+       +------------+
  xx  LAN   x                     + switch +-------| ISP router |
  x        xx                     +--+-----+       +------------+
  xx   xxxxx      +----------+       |
   xxxxx   +------+ router-b +-------+
                  +----------+

I dumped this in a pastebin, in case my mail client mauls
it..http://pastebin.com/rDTDMA7j

In this scenario, router-a and router-b are running FreeBSD, with CARP
to provide a virtual IP for failover. The two routers act in a
failover manner, with router-b taking over the virtual IP upon failure
of router-a. The goal is to maintain the fast failover (seconds) that
I get from CARP in non-BGP configurations. I am wondering if the
following method is a common/feasible/best solution.

Under normal conditions.
* BOTH router-a and router-b establish BGP sessions to the ISP. This
way, each router has a copy of the BGP routing table in memory, ready
to go.
* router-a advertises my prefixes to the ISP router.
* all regular traffic is handled by router-a.

If router-a fails.
* Programmatically update the router-b BIRD config to begin
advertising prefixes.
* router-b already has the BGP table in memory, so routing can resume
immediately.

Is there a better way to achieve this? Will my ISP laugh at me when I
ask them to assign me a /29, and allow me to run two BGP sessions?

Thank you!
TJ

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