EIGRP Mismatched masks

TASK

EIGRPでネイバとのサブネットマスクが異なるとどうなるのか?

DIAGRAM

 

CONFIG

hostname R1
!
interface FastEthernet0/0
 ip address 10.1.2.1 255.255.255.0
 no shutdown
!
interface FastEthernet0/1
 ip address 10.1.3.1 255.255.255.0
 no shutdown
!
router eigrp 65000
 network 10.1.2.1 0.0.0.0
 network 10.1.3.1 0.0.0.0
 eigrp router-id 10.0.0.1
!
end
hostname R2
!
interface FastEthernet0/0
 ip address 10.1.2.2 255.255.255.0
 no shutdown
!
interface FastEthernet0/1
 ip address 10.2.3.2 255.255.255.0
 no shutdown
!
router eigrp 65000
 network 10.1.2.2 0.0.0.0
 network 10.2.3.2 0.0.0.0
 eigrp router-id 10.0.0.2
!
end
hostname R3
!
interface FastEthernet0/0
 ip address 10.1.3.3 255.255.255.0
 no shutdown
!
interface FastEthernet0/1
 ip address 10.2.3.3 255.255.255.128
 no shutdown
!
router eigrp 65000
 network 10.1.3.3 0.0.0.0
 network 10.2.3.3 0.0.0.0
 eigrp router-id 10.0.0.3
!
end

VERIFY

  • ネイバーは張れている
R1#sh ip ei nei
EIGRP-IPv4 Neighbors for AS(65000)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
1   10.1.3.3                Fa0/1                    13 00:04:56   19   114  0  7
0   10.1.2.2                Fa0/0                    14 00:08:27   31   186  0  16
R1#

R2#sh ip ei nei
EIGRP-IPv4 Neighbors for AS(65000)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
1   10.2.3.3                Fa0/1                    14 00:05:12    4   100  0  8
0   10.1.2.1                Fa0/0                    13 00:08:54   34   204  0  13
R2#

R3#sh ip ei nei
EIGRP-IPv4 Neighbors for AS(65000)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
1   10.2.3.2                Fa0/1                    11 00:05:23   26   156  0  17
0   10.1.3.1                Fa0/0                    11 00:05:34 1037  5000  0  12
R3#

 

  • R2のshow ip route に違和感が・・・
R1#sh ip ro | b Gate
Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
C        10.1.2.0/24 is directly connected, FastEthernet0/0
L        10.1.2.1/32 is directly connected, FastEthernet0/0
C        10.1.3.0/24 is directly connected, FastEthernet0/1
L        10.1.3.1/32 is directly connected, FastEthernet0/1
D        10.2.3.0/24 [90/30720] via 10.1.2.2, 00:07:18, FastEthernet0/0
D        10.2.3.0/25 [90/30720] via 10.1.3.3, 00:06:23, FastEthernet0/1
R1#

R2#sh ip ro | b Gate
Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
C        10.1.2.0/24 is directly connected, FastEthernet0/0
L        10.1.2.2/32 is directly connected, FastEthernet0/0
D        10.1.3.0/24 [90/30720] via 10.2.3.3, 00:06:57, FastEthernet0/1
                     [90/30720] via 10.1.2.1, 00:06:57, FastEthernet0/0
C        10.2.3.0/24 is directly connected, FastEthernet0/1
D        10.2.3.0/25 [90/33280] via 10.1.2.1, 00:06:59, FastEthernet0/0
L        10.2.3.2/32 is directly connected, FastEthernet0/1
R2#

R3#sh ip ro | b Gate
Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
D        10.1.2.0/24 [90/30720] via 10.2.3.2, 00:07:10, FastEthernet0/1
                     [90/30720] via 10.1.3.1, 00:07:10, FastEthernet0/0
C        10.1.3.0/24 is directly connected, FastEthernet0/0
L        10.1.3.3/32 is directly connected, FastEthernet0/0
D        10.2.3.0/24 [90/33280] via 10.1.3.1, 00:07:20, FastEthernet0/0
C        10.2.3.0/25 is directly connected, FastEthernet0/1
L        10.2.3.3/32 is directly connected, FastEthernet0/1
R3#

 

  • 遠回りするがLocal routeにより到達はできるが、同じセグメントの異なるアドレスだと周り続ける
R2#traceroute 10.2.3.3
Type escape sequence to abort.
Tracing the route to 10.2.3.3
VRF info: (vrf in name/id, vrf out name/id)
  1 10.1.2.1 32 msec 28 msec 8 msec
  2 10.1.3.3 8 msec 24 msec 20 msec
R2#
R2#traceroute 10.2.3.4
Type escape sequence to abort.
Tracing the route to 10.2.3.4
VRF info: (vrf in name/id, vrf out name/id)
  1 10.1.2.1 40 msec 8 msec 8 msec
  2 10.1.3.3 20 msec 28 msec 20 msec
  3 10.2.3.2 20 msec 20 msec 20 msec
  4 10.1.2.1 48 msec 36 msec 40 msec
  5 10.1.3.3 36 msec 44 msec 52 msec
  6 10.2.3.2 48 msec 36 msec 36 msec
  7 10.1.2.1 56 msec 56 msec 56 msec
  8 10.1.3.3 60 msec 72 msec 68 msec
  9 10.2.3.2 68 msec 56 msec 68 msec
 10 10.1.2.1 88 msec 76 msec 76 msec
 11 10.1.3.3 76 msec 84 msec 92 msec
 12 10.2.3.2 92 msec 76 msec 80 msec
 13 10.1.2.1 96 msec 80 msec 88 msec
 14 10.1.3.3 96 msec 100 msec 96 msec
 15 10.2.3.2 104 msec 92 msec 96 msec
 16 10.1.2.1 120 msec 108 msec 108 msec
 17 10.1.3.3 108 msec 116 msec 116 msec
 18 10.2.3.2 124 msec 116 msec 116 msec
 19 10.1.2.1 136 msec 136 msec 140 msec
 20 10.1.3.3 140 msec 148 msec 144 msec
 21 10.2.3.2 152 msec 136 msec 136 msec
 22 10.1.2.1 156 msec 160 msec 160 msec
 23 10.1.3.3 148 msec 164 msec 160 msec
 24 10.2.3.2 160 msec 156 msec 156 msec
 25 10.1.2.1 176 msec 172 msec 168 msec
 26 10.1.3.3 160 msec 176 msec 180 msec
 27 10.2.3.2 184 msec 172 msec 180 msec
 28 10.1.2.1 192 msec 188 msec 184 msec
 29 10.1.3.3 168 msec 112 msec 108 msec
 30 10.2.3.2 112 msec 108 msec 104 msec
R2#

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