There is more than one possible solution for this challenge. Feel free to post your proposed answer in the comments section. We will try to keep comments hidden from public view, so that the fun isn’t spoiled for others. Also, don’t feel bad if the answer(s) aren’t immediately apparent. A number of very bright people have been puzzled by this scenario. Answers will be posted on Friday, September 18th.
Scenario:
R1 and R2 are configured with their FastEthernet interfaces on the same subnet. R1 will be forming an OSPF neighbor adjacency to R2 over the FastEthernet interface, and will also be advertising some loopback networks into OSPF.
R1’s Relevant Configuration:
interface Loopback1 ip address 1.1.1.1 255.255.255.255 interface Loopback11 ip address 11.11.11.11 255.255.255.255 interface Loopback111 ip address 111.111.111.111 255.255.255.255 interface FastEthernet0/0 ip address 150.10.12.1 255.255.255.0 no shut
R2’s Relevant Configuration:
interface FastEthernet0/0 ip address 150.10.12.2 255.255.255.0 no shut router ospf 1 network 150.10.12.0 0.0.0.255 area 0
Challenge:
Your task is to configure R1 while meeting all of the following criteria for requirements and restrictions:
- R2 should see the networks 1.1.1.1/32, 11.11.11.11/32, and 111.111.111.111/32 as OSPF routes in R2’s routing table, but they should not appear as IA, E2, or E1.
- The output of “show ip ospf neighbor” on R2 should show 11.11.11.11 as the Neighbor ID for the adjacency to R1, even if R1 is reloaded. No other Neighbor IDs should show up on R2.
- You are not allowed to use the “router-id” command on R1.
- You are not permitted to shut down any interfaces on R1, or remove any of the existing configuration on R1.
- No additional configuration may be added to R2, all configuration for this challenge is done on R1.
About Marvin Greenlee, CCIE #12237:
Marvin Greenlee brings years of valuable experience in technical consulting and training. In addition to his on-the-job experience as a Cisco employee, he has written, edited, and reviewed several books and training materials focused on CCIE certification topics. Mr. Greenlee has earned a favorable reputation in the CCIE Lab training community as an active participant on various message boards and email lists. Marvin is responsible for instructor-led training, self-study product development and support.
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59 Responses to “Have you seen my Router ID?”
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Loopback11
ip address 11.11.11.11 255.255.255.255
!
interface Loopback111
ip address 111.111.111.111 255.255.255.255
!
interface FastEthernet0/0
ip address 150.10.12.1 255.255.255.0
duplex auto
speed auto
!
router ospf 2
router-id 111.111.111.111
log-adjacency-changes
!
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 11.11.11.11 0.0.0.0 area 0
network 111.111.111.111 0.0.0.0 area 0
network 150.10.12.1 0.0.0.0 area 0
!
ip http server
ip forward-protocol nd
!
!
!
the idea is to use the lo111 in another ospf process using the router-id command
Heres my take on it
Config on R1 :
int loop 0
descr bogus network for ospf 1 to run
ip address 2.2.2.2 255.255.255.255
interface Loopback1
ip address 1.1.1.1 255.255.255.255
interface Loopback11
ip address 11.11.11.11 255.255.255.255
interface Loopback111
ip address 111.111.111.111 255.255.255.255
interface FastEthernet0/0
ip address 150.10.12.1 255.255.255.0
no shut
Router ospf 1
network 2.2.2.0 0.0.0.255 area 0
Router ospf 10
netwo 150.10.12.0 0.0.0.255 area 0
netwo 1.1.1.0 0.0.0.255 area 0
netwo 11.11.11.0 0.0.0.255 area 0
netwo 111.111.111.0 0.0.0.255 area 0
!
Now, the ospf process 1 takes the 111.111.111.111 as its router-id.
and process 10, wich im using to form adjencencie with R2, is getting router-ID 11.11.11.11 as demanded.
The only buggah, is that on R2 is see the right addresses as /32 hosts pr. default, but Im also seeing the classfull bit 1.0.0.0/8.
It wasnt mentioned that this was NOT ok, so Im just leaving it there
Cool task! Thx – bring on some more please!!
/KelvinDam
This is what I found :
By configuring an additional ospf process, the 111.111.111.111 loopback address will not be available for the second ospf process. As a result, this process will then have the desired router-id of 11.11.11.11. The required routers are then simply advertised as intra-area router using the network command.
router ospf 1
log-adjacency-changes
!
router ospf 2
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 11.11.11.11 0.0.0.0 area 0
network 111.111.111.111 0.0.0.0 area 0
network 150.10.12.1 0.0.0.0 area 0
!
R2#sh ip ro
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
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 150.10.12.1, 00:00:30, Ethernet0/0
111.0.0.0/32 is subnetted, 1 subnets
O 111.111.111.111 [110/11] via 150.10.12.1, 00:00:30, Ethernet0/0
11.0.0.0/32 is subnetted, 1 subnets
O 11.11.11.11 [110/11] via 150.10.12.1, 00:00:30, Ethernet0/0
150.10.0.0/24 is subnetted, 1 subnets
C 150.10.12.0 is directly connected, Ethernet0/0
R2#
R2#sh ip osp n
Neighbor ID Pri State Dead Time Address Interface
11.11.11.11 1 FULL/BDR 00:00:31 150.10.12.1 Ethernet0/0
R2#
First the confirmation:
r2#sh ip ospf nei
Neighbor ID Pri State Dead Time Address Interface
11.11.11.11 1 FULL/BDR 00:00:32 150.10.12.1 Ethernet0/0
r2#sh ip route ospf
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 150.10.12.1, 00:02:24, Ethernet0/0
111.0.0.0/32 is subnetted, 1 subnets
O 111.111.111.111 [110/11] via 150.10.12.1, 00:02:24, Ethernet0/0
11.0.0.0/32 is subnetted, 1 subnets
O 11.11.11.11 [110/11] via 150.10.12.1, 00:02:24, Ethernet0/0
Now the important parts of the R1 config:
interface Loopback1
ip address 1.1.1.1 255.255.255.255
!
interface Loopback11
ip address 11.11.11.11 255.255.255.255
!
interface Loopback111
ip address 111.111.111.111 255.255.255.255
!
interface Loopback888
ip vrf forwarding TEST
ip address 111.111.111.111 255.255.255.255
!
interface Vlan1
ip address 150.10.12.1 255.255.255.0
!
router ospf 2 vrf TEST
log-adjacency-changes
network 111.111.111.111 0.0.0.0 area 0
!
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 11.11.11.11 0.0.0.0 area 0
network 111.111.111.111 0.0.0.0 area 0
network 150.10.12.0 0.0.0.255 area 0
As usual after hitting submit I found one line missing:
ip vrf TEST
okay, next attempt at an answer since when i labbed up the dampening thing it didn’t work. create a new ospf process 2 and have everything be a part of that process.
process 1 will use 111.111.111 and then process 2 will use 11.11.11.11 because router-id’s have to be unique.
-steve_m
On R1
Router ospf 1
network 11.11.11.11 0.0.0.0 area 0
network 1.1.1.1 0.0.0.0 area 0
network 111.111.111.111 0.0.0.0 area 0
passive-interface lo1
passive-interface lo111
R1
Router ospf 1
router-id 11.11.11.11
network 11.11.11.11 0.0.0.0 area 0
network 1.1.1.1 0.0.0.0 area 0
network 111.111.111.111 0.0.0.0 area 0
interface Loopback11
ip address 11.11.11.11 255.255.255.255
ip ospf priority 10
Rgrd, Ivo