I have a two 6509 with MSFC running EIGRP as a routing protocol for 20 VLANs in VTP Domain. Now Vlans 2 to 5 has a vlan interface on 6509A_MSFC and Vlans 6 to 10 has a interface vlan on 6509B_MSFC. Also Vlans 11 to 20 has a vlan interface on both MSFC. All the interface Ip subnets are in EIGRP route process.
Now all the routes between the MSFC's shows as learn from 10 vlan interfaces (int vlan 11 to 20). Here two MSFC are connected through one Gigabit SX interface.
Now here is multiple paths for Neighboring MSFC, Is it fine to have a multiple path between two MSFC or should I use only one path and other vlans (11 to 19) configured as a passive EIGRP interface and use only Vlan 20 as a active interface?
I do not fully understand your network configuration, but personally I would configure all VLANS on Both MSFC's, and run HSRP between them - this will provide redundancy/failover in the event of one MSFC failing. You could use priority (eg...standby 10 priority 105) to load balance 50% of your vlans on one MSFC and the other 50% on the other MSFC.
There are no problems with creating multiple paths between your msfc's as far as routing is concerned - however I would bundle your parallel links into a Channel-group to prevent spanning-tree from blocking all exept one of your inter-msfc links.
Hope this helps,
The question is: "how many parallel paths?" One or two is going to be fine, but when you get much over two parallel paths between the two MFSCs, I would start using passive interface to cut some of them down. In general, I actually don't recommend putting transit traffic on links with hosts and servers on them, either, but that may not be possible in this case.