Similar to rip it will auto summary a network when crosses a major network boundary
you can disable autosummary under router eigrp 1
no auto-summary
In eigrp you can have vlsm within the same major network
In rip we saw the blackhole affect of auto-summarisation where the router recieves a
summary on multiple interface and when it comes to routing to a specfic network it is
unsure which interface to send out and does a round robin depending on your
loadbalancing sending down which blackholes some of the traffic
EIGRP has a defense mechanism against this using the discard route or the null route
LAB
----
OK for the lab we will use the 4 switches sw1 connected to sw3 sw3 connected to sw4
and sw4 connected to sw2.
All switches will be configured with eigrp with default auto summary on
THe switches will use 155.10.0.0/30 on there links while there loopbacks will be
150.10.0.0/32 so in effect the loopbacks will be crossing the major network boundary
and should be summarised.
SW1
-=--
switch1(config)#router eigrp 1
switch1(config-router)#network 155.10.0.0 0.0.0.3
switch1(config-router)#network 155.10.0.4 0.0.0.3
switch1(config-router)#network 150.10.0.1 0.0.0.0
sw2
----
switch2(config)#router eigrp 1
switch2(config-router)#network 150.10.0.2 0.0.0.0
switch2(config-router)#network 155.10.0.0 0.0.0.3
switch2(config-router)#
00:19:31: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 155.10.0.2 (Port-channel2) is
up: new adjacency
sw3
---
switch3(config)#router eigrp 1
switch3(config-router)#network 155.10.0.4 0.0.0.3
switch3(config-router)#network 155.10.0.4 0.0.0.3
00:23:15: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 155.10.0.5 (Port-channel5) is
up: new adjacency
switch3(config-router)#network 155.10.0.13 0.0.0.3
switch3(config-router)#network 150.10.0.3 0.0.0.0
sw4
----
switch4(config)#router eigrp 1
switch4(config-router)#network 150.10.0.4 0.0.0.0sh ruswitch4(config-router)#network
155.10.0.13 0.0.0.3
switch4(config-router)#
00:27:14: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 155.10.0.13 (Port-channel8) is
up: new adjacency
switch4(config-router)#network 155.10.0.16 0.0.0.3
switch4(config-router)#
ok all adjacencies are formed i look on switch 2
switch2#sh ip ei
00:32:54: %SYS-5-CONFIG_I: Configured from console by consolegrp neigh
IP-EIGRP neighbors for process 1
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
1 155.10.0.18 Po8 10 00:00:28 1100 5000 0 6
0 155.10.0.2 Po2 14 00:13:27 460 2760 0 14
switch2#
has 2 neighbors and no que count
ok so if we look at the routing table on switch 2
switch2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
155.10.0.0/16 is variably subnetted, 5 subnets, 2 masks
C 155.10.0.16/30 is directly connected, Port-channel8
C 155.10.0.0/30 is directly connected, Port-channel2
D 155.10.0.0/16 is a summary, 00:13:56, Null0
D 155.10.0.4/30 [90/13568] via 155.10.0.2, 00:00:54, Port-channel2
D 155.10.0.12/30 [90/13568] via 155.10.0.18, 00:00:54, Port-channel8
150.10.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 150.10.0.0/16 is a summary, 00:00:54, Null0
C 150.10.0.2/32 is directly connected, Loopback0
switch2#
we are getting the individual networks for 155.10.0 networks
i can ping for example s3 interface to sw1
switch2#ping 155.10.0.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.10.0.6, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
switch2#
but i am not getting the individual routes to the loopbacks like for example all i am
not getting 150.10.0.3
I am getting a route
D 150.10.0.0/16 is a summary, 00:00:54, Null0
pointing at null 0
switch2#ping 150.10.0.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 150.10.0.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
switch2#
i can not ping. Switch 2 already has a local summary route to null0 when i recieve
summarys of the other switches loopback summarised because they are crossing major
network boundary it rejects them as it has a local summary this prevents traffic
beign blackholed but we still have the issue of reachability. The ping is basically
looking at the null 0 route and sent to it this is discard which just get rid it
ok i have done the command
router eigrp 1
no auto-summary
on all 4 switches
on s2
switch2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
155.10.0.0/30 is subnetted, 4 subnets
C 155.10.0.16 is directly connected, Port-channel8
C 155.10.0.0 is directly connected, Port-channel2
D 155.10.0.4 [90/13568] via 155.10.0.2, 00:05:47, Port-channel2
D 155.10.0.12 [90/13568] via 155.10.0.18, 00:05:47, Port-channel8
150.10.0.0/32 is subnetted, 4 subnets
D 150.10.0.4 [90/139008] via 155.10.0.18, 00:05:47, Port-channel8
D 150.10.0.1 [90/139008] via 155.10.0.2, 00:01:36, Port-channel2
C 150.10.0.2 is directly connected, Loopback0
D 150.10.0.3 [90/141568] via 155.10.0.18, 00:00:19, Port-channel8
[90/141568] via 155.10.0.2, 00:00:19, Port-channel2
i can see all loopbacks
switch2#ping 150.10.0.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 150.10.0.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/9 ms
switch2#
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