EIGRP Passive interface
EIGRP do not send any hello messages on passive interface. EIGRP router ignores any EIGRP messages received on the interface its means no neighbors relation but EIGRP still advertises about the connected subnet only if matched with an EIGRP network command.
lets understand it more clearly
let see the configuration:
Topology:-
TASK:
R1(config)#Interface fastethernet 0/0
R1(config-if)#Ip address 10.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#No keepalive
R1(config-if)#Exit
R1(config)#Interface serial 3/0
R1(config-if)#Ip address 1.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#Exit
R5(config)#router eigrp 61234
R5(config-router)#network 50.0.0.0
R5(config-router)#network 4.0.0.0
R5(config-router)#network 3.0.0.0
R5(config-router)#network 3.0.0.0
R5(config-router)#network 2.0.0.0
R5(config-router)#network 1.0.0.0
R5(config-router)#no auto-summary
R5(config-router)#end
lets understand it more clearly
In our diagram we have 4 Routers and a switch, Router_1 and
Router_2. Down side there’s the network 10.1.1.1/8 with a switch connected to
Router_1 and come computers. We need Router_1 have to advertise the network
10.1.1.1/8 to our Autonomous system and of course router_2 but we have one
problem there is no router on 10.1.1.1/8 network. There is no reason to send
EIGRP hello packets on the interface fastethernet 0/0
There is also one big problem it’s a security risk what if someone connect
his computer to our switch with an application and advertise fake routes and he
become EIGRP neighbors with our router1 this is a nightmare.
We do not allow this going to be happening in our autonomous
system. To prevent this going to happen we need passive interface command and
this feature ensure that the network is advertised in EIGRP but this feature
disable hello packets on the interface (
in our case fatethernet 0/0 )
There is option redistribution with the help of this command
we can prevent our nightmare.
let see the configuration:
Topology:-
TASK:
- configure the topology as per the diagram
- assign IP addresses to their interfaces
- configure EIGRP 61234 and advertise all the interfaces
- configure serial 3/1 and 3/3 passive interfaces
R1(config)#Interface fastethernet 0/0
R1(config-if)#Ip address 10.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#No keepalive
R1(config-if)#Exit
R1(config)#Interface serial 3/0
R1(config-if)#Ip address 1.1.1.1 255.0.0.0
R1(config-if)#No shutdown
R1(config-if)#Exit
R2(config)#Interface fastethernet 0/0
R2(config-if)#Ip address 20.1.1.1 255.0.0.0
R2(config-if)#No shutdown
R2(config-if)#No keepalive
R2(config-if)#Exit
R2(config)#Interface serial 3/1
R2(config-if)#Ip address 2.2.2.1 255.0.0.0
R2(config-if)#No shutdown
R2(config-if)#Exit
R3(config)#Interface fastethernet 0/0
R3(config-if)#Ip address 30.1.1.1 255.0.0.0
R3(config-if)#No shutdown
R3(config-if)#No keepalive
R3(config-if)#Exit
R3(config)#Interface serial 3/1
R3(config-if)#Ip address 3.3.3.1 255.0.0.0
R3(config-if)#No shutdown
R3(config-if)#Exit
R4(config)#Interface fastethernet 0/0
R4(config-if)#Ip address 40.1.1.1 255.0.0.0
R4(config-if)#No shutdown
R4(config-if)#No keepalive
R4(config-if)#Exit
R4(config)#Interface serial 3/1
R4(config-if)#Ip address 4.4.4.1 255.0.0.0
R4(config-if)#No shutdown
R4(config-if)#Exit
R5(config)#Interface fastethernet 0/0
R5(config-if)#Ip address 50.1.1.1 255.0.0.0
R5(config-if)#No shutdown
R5(config-if)#No keepalive
R5(config-if)#Exit
R5(config)#Interface serial 3/0
R5(config-if)#Ip address 1.1.1.2 255.0.0.0
R5(config-if)#No shutdown
R5(config-if)#Exit
R5(config)#Interface serial 3/1
R5(config-if)#Ip address 2.2.2.2 255.0.0.0
R5(config-if)#No shutdown
R5(config-if)#Exit
R5(config)#Interface serial 3/2
R5(config-if)#Ip address 3.3.3.2 255.0.0.0
R5(config-if)#No shutdown
R5(config-if)#Exit
R5(config)#Interface serial 3/3
R5(config-if)#Ip address 4.4.4.2 255.0.0.0
R5(config-if)#No shutdown
R5(config-if)#Exit
R1#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.1.1 YES manual up up
Serial3/0 1.1.1.1 YES manual up up
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.1.1 YES manual up up
Serial3/0 1.1.1.1 YES manual up up
R2#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 20.1.1.1 YES manual up up
Serial3/1 2.2.2.1 YES manual up up
R3#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 30.1.1.1 YES manual up up
Serial3/2 3.3.3.1 YES manual up up
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 30.1.1.1 YES manual up up
Serial3/2 3.3.3.1 YES manual up up
R4#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 40.1.1.1 YES manual up up
Serial3/3 4.4.4.1 YES manual up up
R5#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 50.1.1.1 YES manual up up
Serial3/0 1.1.1.2 YES manual up up
Serial3/1 2.2.2.2 YES manual up up
Serial3/2 3.3.3.2 YES manual up up
Serial3/3 4.4.4.2 YES manual up up
R1(config)#router eigrp 61234
R1(config-router)#network 1.0.0.0
R1(config-router)#network 10.0.0.0
R1(config-router)#no auto-summary
R1(config-router)#end
R2(config)#router eigrp 61234
R2(config-router)#network 2.0.0.0
R2(config-router)#network 20.0.0.0
R2(config-router)#no auto-summary
R2(config-router)#end
R3(config)#router eigrp 61234
R3(config-router)#network 3.0.0.0
R3(config-router)#network 30.0.0.0
R3(config-router)#no auto-summary
R3(config-router)#end
R4(config)#router eigrp 61234
R4(config-router)#network 4.0.0.0
R4(config-router)#network 40.0.0.0
R4(config-router)#no auto-summary
R4(config-router)#end
R5(config)#router eigrp 61234
R5(config-router)#network 50.0.0.0
R5(config-router)#network 4.0.0.0
R5(config-router)#network 3.0.0.0
R5(config-router)#network 3.0.0.0
R5(config-router)#network 2.0.0.0
R5(config-router)#network 1.0.0.0
R5(config-router)#no auto-summary
R5(config-router)#end
*Dec 4 23:22:09.967: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 4.4.4.1 (Serial3/3) is up: new adjacency
*Dec 4 23:22:14.343: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 3.3.3.1 (Serial3/2) is up: new adjacency
*Dec 4 23:22:19.375: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 2.2.2.1 (Serial3/1) is up: new adjacency
*Dec 4 23:22:25.239: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 1.1.1.1 (Serial3/0) is up: new adjacency
R5#show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(61234)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
3 1.1.1.1 Se3/0 12 00:04:14 78 468 0 3
2 2.2.2.1 Se3/1 12 00:04:20 79 474 0 5
1 3.3.3.1 Se3/2 14 00:04:25 57 342 0 7
0 4.4.4.1 Se3/3 14 00:04:30 67 402 0 9
R5#show ip route eigrp
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is not set
D 10.0.0.0/8 [90/2172416] via 1.1.1.1, 00:04:21, Serial3/0
D 20.0.0.0/8 [90/2172416] via 2.2.2.1, 00:04:27, Serial3/1
D 30.0.0.0/8 [90/2172416] via 3.3.3.1, 00:04:32, Serial3/2
D 40.0.0.0/8 [90/2172416] via 4.4.4.1, 00:04:37, Serial3/3
R5(config)#router eigrp 61234
R5(config-router)#passive-interface serial 3/1
R5(config-router)#passive-interface serial 3/3
R5(config-router)#end
*Dec 4 23:29:34.627: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 2.2.2.1 (Serial3/1) is down: interface passive
*Dec 4 23:29:40.855: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 4.4.4.1 (Serial3/3) is down: interface passive
*Dec 4 23:22:19.375: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 2.2.2.1 (Serial3/1) is up: new adjacency
*Dec 4 23:22:25.239: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 1.1.1.1 (Serial3/0) is up: new adjacency
R5#show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(61234)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
3 1.1.1.1 Se3/0 12 00:04:14 78 468 0 3
2 2.2.2.1 Se3/1 12 00:04:20 79 474 0 5
1 3.3.3.1 Se3/2 14 00:04:25 57 342 0 7
0 4.4.4.1 Se3/3 14 00:04:30 67 402 0 9
R5#show ip route eigrp
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is not set
D 10.0.0.0/8 [90/2172416] via 1.1.1.1, 00:04:21, Serial3/0
D 20.0.0.0/8 [90/2172416] via 2.2.2.1, 00:04:27, Serial3/1
D 30.0.0.0/8 [90/2172416] via 3.3.3.1, 00:04:32, Serial3/2
D 40.0.0.0/8 [90/2172416] via 4.4.4.1, 00:04:37, Serial3/3
R5(config-router)#passive-interface serial 3/1
R5(config-router)#passive-interface serial 3/3
R5(config-router)#end
*Dec 4 23:29:34.627: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 2.2.2.1 (Serial3/1) is down: interface passive
*Dec 4 23:29:40.855: %DUAL-5-NBRCHANGE: EIGRP-IPv4 61234: Neighbor 4.4.4.1 (Serial3/3) is down: interface passive
R5#show ip eigrp interfaces
EIGRP-IPv4 Interfaces for AS(61234)
Xmit Queue PeerQ Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable Un/Reliable SRTT Un/Reliable Flow Timer Routes
Fa0/0 0 0/0 0/0 0 0/0 0 0
Se3/2 1 0/0 0/0 60 0/16 236 0
Se3/0 1 0/0 0/0 66 0/16 272 0
R5#show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(61234)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
3 1.1.1.1 Se3/0 10 00:08:32 66 396 0 7
1 3.3.3.1 Se3/2 11 00:08:43 60 360 0 11
R5#show ip route eigrp
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is not set
D 10.0.0.0/8 [90/2172416] via 1.1.1.1, 00:08:39, Serial3/0
D 30.0.0.0/8 [90/2172416] via 3.3.3.1, 00:08:50, Serial3/2
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