LC load balcing ISP connection across 2 DC?

The F5 itself can do dynamic routing through zebos (zebos enable in the cli and then vtysh to get the config): http://support.f5.com/kb/en-us/solutions/public/13000/300/sol13332.html (dunno what happend to the docs, anyone who knows?).

 

 

Then it depends on your ISP how they will route your internet networks between the sites. A common method for this is to use BGP or such towards Internet.

 

 

Another method to take into account is to use anycast ranges along with physical ranges.

 

 

Lets say you have 3 x /24 in total. Then siteA could announce x.x.0.0/24 (as anycast) and x.x.1.0/24 as physical range while siteB announces x.x.0.0/24 (as anycast) and x.x.2.0/24 as physical range. The physical ip-addresses will be used for MX-records or if you really want to go to siteB for some reason.

 

 

Usually the BGP would block siteA from seeing siteB (if both uses the same AS) but if you just "import" default route from your ISP then the static route will take care of that part. But this is more of a active-active setup rather than active-passive site-setup.