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Section 2: IP IGP Protocols (28 Points)

Section 2.1: RIP (16 Points)

  • On all RIP router, ensure that version 2 is used under the process.

Add version 2 under the RIP process. You receive no points here; this just ensures your routers behave correctly during the lab.

You should have at this point also enabled RIP for your networks using the network command and as a matter of good practice configured router interfaces that are not part of the RIP domain as passive using the command passive-interface under the RIP process of each router.

  • Ensure that VLSM is supported on advertisements between all RIP routers.

This is just a case of manually configuring the RIP routers to disable auto summarization mainly for the benefit of R3, which would otherwise receive a classfull network 10.0.0.0/8 route from R2. If you have configured this correctly as shown in Example 1-9 on all RIP routers with the resulting routing table shown for R3 in Example 1-10, you have scored 2 points.

Example 1-9 RIP VLSM Configuration on R1, R2, R3, R4, and R6

router rip
 no auto-summary

Example 1-10 R3 RIP Routing Table Output

R3#sh ip route

C    172.16.0.0/16 is directly connected, FastEthernet0/0
     10.0.0.0/8 is variably subnetted, 9 subnets, 3 masks
R       10.100.100.0/28 [120/2] via 172.16.0.1, 00:00:24, FastEthernet0/0
R       10.99.99.0/29 [120/4] via 172.16.0.1, 00:00:24, FastEthernet0/0
R       10.90.90.0/28 [120/1] via 172.16.0.1, 00:00:24, FastEthernet0/0
R       10.80.80.0/24 [120/2] via 172.16.0.1, 00:00:24, FastEthernet0/0
R       10.60.60.0/29 [120/4] via 172.16.0.1, 00:00:26, FastEthernet0/0
R       10.40.40.0/28 [120/3] via 172.16.0.1, 00:00:26, FastEthernet0/0
R       10.6.6.0/29 [120/4] via 172.16.0.1, 00:00:26, FastEthernet0/0
R       10.4.4.0/29 [120/3] via 172.16.0.1, 00:00:26, FastEthernet0/0
R       10.1.1.0/28 [120/2] via 172.16.0.1, 00:00:26, FastEthernet0/0

  • Add a loopback interface with the address of 60.60.60.1/24 onto R3 and advertise this out to R2 but ensure that it is not seen by the rest of your network; do not perform any configuration on R2 or R1.

Add the loopback as Lo0 on R3 and enable the 60.60.60.0/24 network under RIP; this automatically advertises network 60.60.60.0/24 out to R2 and the rest of your RIP network over the 172.16.0.0/16 network, which you should have already configured according to the IGP diagram. The usual method to stop the propagation of this network would be via distribute lists, but the question states that R2 must see the network so you can not put a distribute list out on R3; the question also states that you can not configure R2 or R1 so you will have to configure R3. You need to get back to basics here and recall that RIP has a maximum hop count of 15 with 16 hops marked as unreachable so you will need to ensure that when network 60.60.60.0/24 egresses R3 the hop count is already set at 14. This way when R2 sees the route it knows that it has a hop count of 15 to reach it; it, in turn, will then advertise network 60.60.60.0/24 with a hop count of 16, which is, of course, unreachable and, hence, it will not be included in the routing table of R1 and beyond. To achieve the artificial hop count, an offset-list is required for network 60.60.60.0/24 on R3. If you have configured this correctly as in Example 1-11 with validation shown in Example 1-12 and Example 1-13, you have scored 4 points.

You could have also gained full marks for advertising the loopback interface on R3 within RIP as a connected interface and assigned a metric of 15 to this route, which provides exactly the same result.

Example 1-11 R3 Hop Count Configuration

interface Loopback0
 ip address 60.60.60.1 255.255.255.0
!
router rip
 version 2
 offset-list 1 out 14 FastEthernet0/0
 network 60.0.0.0
 network 172.16.0.0
!
access-list 1 permit 60.60.60.0

Example 1-12 R2 Routing Entry for 60.60.60.0/24

R2#show ip route 60.60.60.0
Routing entry for 60.60.60.0/24
  Known via "rip", distance 120, metric 15
  Redistributing via rip
  Last update from 172.16.0.2 on FastEthernet0/0, 00:00:15 ago
  Routing Descriptor Blocks:
  * 172.16.0.2, from 172.16.0.2, 00:00:15 ago, via FastEthernet0/0
      Route metric is 15, traffic share count is 1

Example 1-13 R1 RIP debug

R1#debug ip rip
2w1d: RIP: received v2 update from 10.90.90.1 on Serial0/0
2w1d:      60.60.60.0 in 16 hops (inaccessible)
2w1d:      172.16.0.0 in 1 hops

  • Configure R3 to unicast its RIP routing updates to R2. Do not use the neighbor command to achieve this but consider using other IP features to aid you.

Normally, you would use the neighbor command in conjunction with passive-interface to ensure that a router unicasts its routing updates instead of multicasting them in the usual manner. To achieve this without the neighbor command, you will need to use NAT to turn a multicast into a unicast; this is your additional IP feature. A simple NAT statement causing any packet with a destination address as a multicast to destination address 224.0.0.9 with the UDP port equal to that of RIP (520) to be converted into a destination address of 172.16.0.1 (R2 FastEthernet0/0) will cause R3 to now unicast its routing updates directly to R3.

If you have configured this correctly as in Example 1-14 and with the resulting output on R2 as shown in Example 1-15, you have scored 6 points.

Example 1-14 R3 NAT Configuration and debug

interface FastEthernet0/0
 ip address 172.16.0.2 255.255.0.0
 ip nat outside
!

ip nat outside source static udp 172.16.0.1 520 224.0.0.9 520 

R3#debug ip nat det
IP NAT detailed debugging is on
R3#clear ip route *
R3#

00:57:29: NAT: i: udp (172.16.0.2, 520) -> (224.0.0.9, 520) [0]
00:57:29: NAT: s=172.16.0.2, d=224.0.0.9->172.16.0.1 [0]  

Example 1-15 R2 RIP debug

R2#debug ip pack det
IP packet debugging is on (detailed)
R2#
00:54:56: IP: s=172.16.0.2 (FastEthernet0/0), d=172.16.0.1 (FastEthernet0/0), len 5
2, rcvd 3
00:54:56:     UDP src=520, dst=520

  • Ensure that VLAN2 is advertised to the RIP domain as a /28 network. Do not use either RIP or EIGRP features to accomplish this. You can, however, configure R6.

VLAN2 has a subnet mask of /24, and as such, the RIP domain would see this as network 10.80.80.0/24.

You could quite easily summarize network 10.80.80.0/24 within RIP or later within EIGRP to change the network to 10.80.80.0/28, but the question clearly states that no RIP or EIGRP feature must be used. The lab rules are also not static routes; policy routing won't help as the network should be present in all routing tables so the only way to get VLAN2 from a /24 into a /28 is to think laterally and add a secondary address on R6 FastEthernet0/0 within the /28 range (i.e., 10.80.80.14/28). This will then ensure the network 10.80.80.0/28 is advertised into the RIP domain.

NOTE

The new RIP advertisement of 10.80.80.0/28 will be received by R1, which already has a connected interface into the real 10.80.80.0/24 network. This is a longer match than its own connected interface and, hence, will cause suboptimal routing for R1 to communicate on VLAN2 within the range of the /24 subnet. A distribute-list must be used on R1 to filter this network. Remember that the RIP route for this network could arrive on both the Frame Relay interface and the BRI if the Frame Relay network fails later in the lab; as such the distribute-list is required in-bound on both interfaces.

If you have configured this correctly including filtering network 10.80.80.0/28 from entering R1 as in Example 1-16 and Example 1-17, you have scored 4 points. If you have only configured the distribute-list on the Frame Relay network, you have only scored 2 points.

Example 1-16 R6 Secondary Address Configuration

interface FastEthernet0/0
 ip address 10.80.80.14 255.255.255.240 secondary
 ip address 10.80.80.2 255.255.255.0

Example 1-17 R1 RIP Distribute-List Configuration

router rip
distribute-list 1 in Serial0/1.101
 distribute-list 1 in BRI0/0
!
access-list 1 deny   10.80.80.0 0.0.0.15 
access-list 1 permit any

Section 2.2: EIGRP (5 Points)

You should have configured EIGRP using AS10 as shown in Figure 1-13 on R5, R6, R7, and R8. R6 has RIP enabled on the Frame Relay network, so you can either use a network statement for each EIGRP required interface with an inverse mask or simply use the passive-interface command as required. All EIGRP routers should also have auto summarization disabled using the command no auto-summary. No extra points here in Lab 1, but you will find in later labs that you will earn points for the correct basic configuration.

NOTE

The IGP questions do not stipulate if R6 should advertise it's loopback interface via RIP or EIGRP because R6 runs both protocols, in this case it is prudent to do so in both instances.

  • R8 is very low on memory and CPU resource; accommodate this information within the configuration on R8.

EIGRP supports stub routing, which improves network stability, reduces resource, and simplifies configuration. R8 does not participate in any summary advertisements so it purely requires eigrp stub connected configured under its EIGRP process to ensure that its connected interfaces are successfully advertised out to its neighbors. If you have configured this correctly as in Example 1-18, you have scored 3 points.

Example 1-18 R8 EIGRP Stub-Routing Configuration and R6 EIGRP Neighbor Output

router eigrp 10
 network 10.0.0.0
 no auto-summary
 eigrp stub connected

R6#sh ip eigrp neighbors detail
IP-EIGRP neighbors for process 10
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq Type
                                            (sec)         (ms)       Cnt Num
2   10.99.99.2              Se0/0            167 05:30:02    4   200  0  2
   Version 12.2/1.2, Retrans: 6, Retries: 0
1   10.60.60.2              Fa0/1             12 05:30:02  340  2040  0  3
   Version 12.1/1.2, Retrans: 0, Retries: 0
0   10.80.80.3              Fa0/0             14 05:30:05    9   200  0  4
   Version 12.1/1.2, Retrans: 2, Retries: 0
   Stub Peer Advertising ( CONNECTED ) Routes

  • Configure R8 to have an EIGRP hello interval of 25 seconds on its FastEthernet0/0 interface.

The EIGRP hello interval is by default set at 5 seconds for FastEthernet. This is not a difficult question but you must ensure if you are changing any EIGRP interval that you should also configure that of your neighbors on the common subnet exactly the same otherwise your neighbor adjacencies will be fluctuating as will your routing table. You should also be aware that the EIGRP hold interval should be three times that of the hello interval otherwise you will experience difficulties in maintaining your neighbor relationship. You should, therefore, configure the ip hold-time eigrp interval on R8 under the FastEthernet0/0 as 75 seconds. Configure R6 under its FastEthernet0/0 with the same configuration as R8 as it is a neighbor to R8 on VLAN2. If you have configured this correctly as shown in Example 1-19, you have scored 2 points.

Example 1-19 R8 and R6 EIGRP Hello and Hold Interval Configuration

interface FastEthernet0/0
 ip hello-interval eigrp 10 25
 ip hold-time eigrp 10 75

Section 2.3: Redistribution (7 Points)

  • Redistribute IGP protocols to ensure full IP visibility between all routers.

You can see via the IGP diagram in Figure 1-13 that there will only be one redistribution point required, this being R6.

Mutual redistribution between RIP and EIGRP is required. Don't forget your default metrics under each process otherwise the different protocols will have no means of applying relevant metrics to the routes you wish to advertise. If you have configured your redistribution correctly as shown in Example 1-20 and Example 1-21 and have full IP visibility of all networks, you have scored 4 points.

Example 1-20 R6 EIGRP Redistribution to RIP Configuration

router rip
 version 2
 redistribute eigrp 10
 passive-interface default
 no passive-interface Serial5/0.103
 network 10.0.0.0
 default-metric 3
 no auto-summary

Example 1-21 R6 RIP Redistribution to EIGRP Configuration

router eigrp 10
 redistribute rip
 passive-interface default
 no passive-interface FastEthernet0/0
 no passive-interface ATM1/0.99
 no passive-interface FastEthernet4/0
 network 10.0.0.0
 default-metric 100000 0 255 1 1500
 no auto-summary

  • As a safety precaution, ensure that R6 can not learn the EIGRP routes it previously advertised into the RIP domain back from R4.

This question is just a straightforward practice of distribute lists and ensuring that the correct networks are filtered. In this scenario, R6 would ignore any routes back from RIP to which it had redistributed into RIP originally from EIGRP because of the external EIGRP route feature (any routes redistributed into EIGRP are subject to an increased Administritive Distance from 90 to 170). The redistributed RIP routes would simply be ignored. To answer the question as requested, though, you will need to configure a distribute-list within RIP on R6 Serial5/0.103, which blocks the EIGRP routes that R6 advertises out to the RIP domain. Do not include the connected interfaces on R6 in your ACL as these would be advertised within the RIP domain anyway and not redistributed into RIP from EIGRP. If you have configured this correctly as shown in Example 1-22, you have scored 3 points.

Example 1-22 R6 Distribution List Configuration

router rip
 distribute-list 1 in Serial5/0.103
!
access-list 1 deny   10.8.8.8
access-list 1 deny   10.5.5.4 0.0.0.3
access-list 1 deny   10.7.7.0 0.0.0.15
access-list 1 deny   10.50.50.0 0.0.0.7
access-list 1 permit any

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