BIG-IP DNS - dynamic LB method "hops"
I'd like to ask you for details about dynamic LB method "hops". Documentation description is nice and short, but without details:
"BIG-IP GTM distributes DNS name resolution requests to a virtual server in the data center that has the fewest router hops from the client's LDNS. BIG-IP GTM uses the traceroute utility to track the number of router hops between a client's LDNS and each data center."
The question is, how can GTM to know the number of hops between client's LDNS and each data center. I think, there is only one possibilities: the number of hops between client's LDNS and datacenter is summary of hops between (GTM and LDNS) and (GTM and data center).
If it's true, not always will be decision correct. For example: client and first data center is in the same city (second DC and GTM in another city). traceroute between client's LDNS and first DC is 'one hop', but GTM calculates calculates GTM-to-LDNS as 2hops and GTM-to-first-DC as 2hops. in summary 4hops for first DC. for second DC is GTM-to-LDNS 2hops, and GTM-to-second-DC 1hop. in summary 3hops. in the final client's request is routed to second DC (3 hops) and not first DC (1 hop).
can anybody (f5 technician) explain me this dynamic method?
thanks, martin