Diffrenece between IP route cost and Routing group cost?

typically the routing group is the class off traffic or your traffic priority. and ip routing metric dictates what preference the routing takes in terms of which route out of many to take in order to get to a particular destination, so effectively least cost routing.
to give higher priority to the traffic in terms of bandwidth you would need to decrease traffic priority for say a-b and increase b-c.
that would be th routing though.

however it is likely that your traffic also has QOS so a-b is guarenteed 256kb b-c gets 128kbps
a-c gets 128kbps for example each of them gets a burst if there is bandwidth available.
i would probably do it more along the lines
A-B (RG=5 IP=5)
B-C (RG=25 IP=5)
A-C(RG=10 IP=5)
given that you are using routing groups i am assuming that you are using an MPLS of some sorts or an agregated T1, so each site would have a single link and all the traffic is routed accordingly.

with the above scenario that i have given i am giving each of the routing groups the same as it was but changing the cost of the routes to be the same as having them different does not make a difference as the destination are all differnt in which case the routing cost is irrelevent.

assuming that site A has a 2mb
Site B and C have a 1mb each.

do this to the traffic QOS.
this is all done from site a so this will have to be adapted at each of the other sites to reflect that traffic.
A-B has the most traffic so give that 1mb guarenteed (50% total bandwidth) burst 2 2mbps (Full bandwidth)
B-C has the least so give it 128kbps (12.5% total site B and C bandwidth) burst to 512 kbps (50% B and C bandwidth)
A-C has a bit more traffic  so 512kbps (50% of site C link) Burst to 768kbps (75% of C bandwidth)

you could then take it one step further and within the RG priorities increase the number of RG so 3 per route and put different protocols into the 3 according to the priority of that traffic.
so for instance give Citrix high priority and smtp low priority for each link.

This will help give the applications that need it better performance, and lower priority to the others.

Hope this makes sense given the litle information given this is how i would do it.

Thank you for your reply. But your explanation is so technical. I am not good enough to understand. Would you mind explaing me simpler?

What I am confusing is that I think IP route decide which route to take right? Does it take priority over routing group cost?

In my example, if I just increase my A-B Routing group cost to 20. But I still keep my IP route cost=5 (still lower than A-C IP route cost=10). The route is still going to take same route right? If same route is used, the bandwidth problem still not fixed right?

Thank you very much!! Thank you for your time. It's very clear for me... but I still don't understand the last sentence ... "a routing group would decide along that route which traffic from site A, to either site b or site c takes priority. so 70%of bandwidth to site B and 30%to site C."

Do you mean routing group cost take prority over Ip route cost?

no they are serving 2 different purposes they work together.
ip route is for the path and routing group is for the priority of the traffic across that path

so one physical path has multiple destinations routing groups would decide how much bandwidth each of them can use

From your example, I understand that for IP route, it will always go for the lowest cost first and if the path fails, then it go for the second lower path.

you are saying routing group is for the priority of the traffic across that path....

Here is still confusing me... in your example,
route 3 = 192.168.3.0/24  192.168.1.1  metric 5 (A->B->C)
route 2 = 192.168.3.0/24  192.168.1.2  metric 10 (A->C)

If the routing group cost for A->C is lower than A->B->C
which path will use?

that example will go route 3 then if that fails route 2
it should be the other way around in terms of metric
my example did not give a-b-c
i would do
a-b metric 5
a-c-b metric 25
a-c metric 5
a-b-c metric 25
that way traffic from a-c would o directly first and as an alternative would thne go via b
 so this scenario is in a triangle these are your primary routes
                                   A
   RG 20    Metric  5  /     \  metric 5 RG 10
                                B --  C
                               metric 5
                                 RG10
secondary would be to route with a higher metric ie 25 through alternative sites a-b-c and a-c-b