back to eigrp...

the show ip eigrp interfaces command will not show a passive interface in its ouput...  see below...

r1#sh ip eigrp int
EIGRP-IPv4 Interfaces for AS(1)
                              Xmit Queue   PeerQ        Mean   Pacing Time   Multicast    Pending
Interface              Peers  Un/Reliable  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Se1/0                    1        0/0       0/0           9       5/195        235           0
Lo0                      0        0/0       0/0           0       0/0            0           0
r1#config t
Enter configuration commands, one per line.  End with CNTL/Z.
r1(config)#router eigrp 1
r1(config-router)#passive-int lo0
r1(config-router)#end
r1#
*Oct  7 07:47:12: %SYS-5-CONFIG_I: Configured from console by console
r1#sh ip eigrp int
EIGRP-IPv4 Interfaces for AS(1)
                              Xmit Queue   PeerQ        Mean   Pacing Time   Multicast    Pending
Interface              Peers  Un/Reliable  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Se1/0                    1        0/0       0/0           9       5/195        235           0
r1#

to change the hello interval for an eigrp interface use ip hello-interval eigrp (asn) (time)... display the change with sh ip eigrp int detail (int)

r1(config-if)#do sh ip eigrp int det f0/0
EIGRP-IPv4 Interfaces for AS(1)
                              Xmit Queue   PeerQ        Mean   Pacing Time   Multicast    Pending
Interface              Peers  Un/Reliable  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Fa0/0                    1        0/0       0/0          36       0/0           50           0
  Hello-interval is 9, Hold-time is 15

with eigrp, mismatched ip subnets and passive-interfaces will prevent neighborships from forming...  mismatched hello-times and duplicate router-id's have no bearing on neighborships from forming...