crookbook eigrp summ...

add loopbacks to r1... add auto-summary...

it is very contrived, suck it up...

interface Loopback1
 ip address 192.168.1.1 255.255.255.252
!
interface Loopback2
 ip address 192.168.1.9 255.255.255.252
!
interface Loopback3
 ip address 192.168.1.17 255.255.255.252

r2#sh ip route eigrp

Gateway of last resort is not set

D     1.0.0.0/8 [90/2297856] via 10.1.1.1, 00:00:16, Serial2/0
D     192.168.1.0/24 [90/2297856] via 10.1.1.1, 00:00:16, Serial2/0

auto summary makes summarization at the classful border...

lose it...

r2#sh ip route eigrp

Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets
D        1.1.1.0 [90/2297856] via 10.1.1.1, 00:00:11, Serial2/0
      192.168.1.0/30 is subnetted, 3 subnets
D        192.168.1.0 [90/2297856] via 10.1.1.1, 00:00:11, Serial2/0
D        192.168.1.8 [90/2297856] via 10.1.1.1, 00:00:11, Serial2/0
D        192.168.1.16 [90/2297856] via 10.1.1.1, 00:00:11, Serial2/0

and you get them all...

to summarize at the longest prefix, count...

0 to 16 includes 0 and that means 17, so the summary needs to be more than 16 and less than 32...  256 minus 32 = 224 or /24 + 3 or /27...

int s2/0
ip summary-add eigrp 1 192.168.1.0 255.255.255.224

r2#sh ip route eigrp

Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets
D        1.1.1.0 [90/2297856] via 10.1.1.1, 00:06:45, Serial2/0
      192.168.1.0/27 is subnetted, 1 subnets
D        192.168.1.0 [90/2297856] via 10.1.1.1, 00:00:16, Serial2/0

/28 doesn't get it...

int s2/0
ip summary-add eigrp 1 192.168.1.0 255.255.255.240

r2#sh ip route eigrp

Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets
D        1.1.1.0 [90/2297856] via 10.1.1.1, 00:09:25, Serial2/0
      192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
D        192.168.1.0/27 [90/2297856] via 10.1.1.1, 00:02:56, Serial2/0
D        192.168.1.0/28 [90/2297856] via 10.1.1.1, 00:00:42, Serial2/0

this has been a public service announcement...