Troubleshooting Exercises
Figure 3-37 shows the internetwork diagram for Troubleshooting Exercises 1 through 6.
| 1: | Example 3-165 shows the BGP configuration of router R2 in Figure 3-37.
Example 3-165 BGP Configuration of Router R2
router bgp 10
no synchronization
network 0.0.0.0
neighbor 172.16.254.2 remote-as 10
neighbor 172.16.254.2 next-hop-self
neighbor 172.16.254.6 remote-as 10
neighbor 172.16.254.6 next-hop-self
no auto-summary
!
ip classless
ip route 0.0.0.0 0.0.0.0 Ethernet10
Example 3-166 shows the BGP table and routing table for R2. Although there are routes to the destinations in the autonomous systems shown in Figure 3-37, pings to those destinations fail. Why?
Example 3-166 The BGP and Routing Tables of R2 in Figure 3-37
R2#show ip bgp
BGP table version is 7, local router ID is 10.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 0.0.0.0 0 32768 i
*>i172.17.0.0 172.16.255.21 0 100 0 60 i
*>i172.18.0.0 172.16.255.9 0 100 0 30 i
*>i172.19.0.0 172.16.255.5 0 100 0 20 i
*>i172.20.0.0 172.16.255.13 0 100 0 40 i
*>i172.21.0.0 172.16.255.17 0 100 0 50 i
R2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
10.0.0.0 255.255.255.0 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, Ethernet11
B 172.20.0.0 [200/0] via 172.16.255.13, 00:01:15
B 172.21.0.0 [200/0] via 172.16.255.17, 00:01:16
172.16.0.0 255.255.255.252 is subnetted, 2 subnets
C 172.16.254.0 is directly connected, Ethernet12
C 172.16.254.4 is directly connected, Ethernet13
B 172.17.0.0 [200/0] via 172.16.255.21, 00:01:16
B 172.18.0.0 [200/0] via 172.16.255.9, 00:00:59
B 172.19.0.0 [200/0] via 172.16.255.5, 00:00:59
S* 0.0.0.0 0.0.0.0 is directly connected, Ethernet10
R2#ping 172.17.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.17.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#
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| | 2: | Example 3-167 shows debug output from routers R1 and R5 in Figure 3-37. What problem do the messages indicate?
Example 3-167 debug Output from R1 and R5 in Figure 3-37
R1#debug ip bgp
BGP debugging is on
R1#
BGP: 172.16.255.5 open active, local address 172.16.255.6
BGP: 172.16.255.5 sending OPEN, version 4
BGP: 172.16.255.5 received NOTIFICATION 2/2 (peer in wrong AS) 2 bytes 000A
BGP: 172.16.255.5 closing
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R5#
6d08h: BGP: 172.16.255.6 open active, delay 28272ms
6d08h: BGP: 172.16.255.6 open active, local address 172.16.255.5
6d08h: BGP: 172.16.255.6 sending OPEN, version 4
6d08h: BGP: 172.16.255.6 OPEN rcvd, version 4
6d08h: BGP: 172.16.255.6 bad OPEN, remote AS is 10, expected 30
6d08h: BGP: 172.16.255.6 sending NOTIFICATION 2/2 (peer in wrong AS) 2 bytes 000A
6d08h: BGP: 172.16.255.6 remote close, state CLOSEWAIT
6d08h: BGP: 172.16.255.6 closing
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| | 3: | Example 3-168 shows the BGP tables of R1 and R3 in Figure 3-37. The first table indicates that 172.17.0.0/24 can be reached either via R6 (172.16.255.25) or R3 (172.16.254.9). Which path is R1 using, and why?
Example 3-168 BGP Tables from R1 and R3 in Figure 3-37
R1#show ip bgp
BGP table version is 8, local router ID is 172.20.7.1
Status codes: s suppressed, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i0.0.0.0 172.16.254.1 0 100 0 i
* i172.17.0.0 172.16.254.9 0 100 0 60 i
*> 172.16.255.25 0 0 60 i
*> 172.18.0.0 172.16.255.9 0 0 30 i
*> 172.19.0.0 172.16.255.5 0 0 20 i
*>i172.20.0.0 172.16.254.9 0 100 0 40 i
*>i172.21.0.0 172.16.254.9 0 100 0 50 i
R1#
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R3#show ip bgp
BGP table version is 5, local router ID is 172.16.255.22
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i0.0.0.0 172.16.254.5 0 100 0 i
* i172.17.0.0 172.16.254.10 0 100 0 60 i
*> 172.16.255.21 0 0 60 i
* i172.18.0.0 172.16.254.10 0 100 0 30 i
* i172.19.0.0 172.16.254.10 0 100 0 20 i
*> 172.20.0.0 172.16.255.13 0 0 40 i
*> 172.21.0.0 172.16.255.17 0 0 50 i
R3#
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| | 4: | Example 3-169 shows the BGP and IGP configurations for R1, R3, R6, and R7 in Figure 3-37.
Example 3-169 BGP and IGP Configurations for Routers R1, R3, R6, and R7
R1
router bgp 10
neighbor 172.16.254.1 remote-as 10
neighbor 172.16.254.1 next-hop-self
neighbor 172.16.254.9 remote-as 10
neighbor 172.16.254.9 next-hop-self
neighbor 172.16.255.5 remote-as 20
neighbor 172.16.255.9 remote-as 30
neighbor 172.16.255.25 remote-as 60
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R3
router bgp 10
neighbor 172.16.254.5 remote-as 10
neighbor 172.16.254.5 next-hop-self
neighbor 172.16.254.10 remote-as 10
neighbor 172.16.254.10 next-hop-self
neighbor 172.16.255.13 remote-as 40
neighbor 172.16.255.17 remote-as 50
neighbor 172.16.255.21 remote-as 60
neighbor 172.16.255.21 next-hop-self
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R6
router eigrp 60
redistribute bgp 60 metric 1000 100 255 1 1500
network 172.17.0.0
!
router bgp 60
network 172.17.0.0
neighbor 172.16.255.26 remote-as 10
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R7
router eigrp 60
redistribute bgp 60 metric 1000 100 255 1 1500
network 172.17.0.0
!
router bgp 60
network 172.17.0.0
neighbor 172.16.255.22 remote-as 10
Example 3-168 shows the BGP tables for R1 and R3. For each of the following destinations, what next-hop address does R6 use? Explain why R6 uses the addresses you name.
Destinations:
172.20.7.102
172.18.58.35
10.53.12.6
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| | 5: | Example 3-170 shows the BGP configurations for R1 and R3 in Figure 3-37.
Example 3-170 BGP Configurations for Routers R1 and R3
R1
router bgp 10
no synchronization
aggregate-address 172.16.0.0 255.255.248.0 summary-only
neighbor 172.16.254.1 remote-as 10
neighbor 172.16.254.1 next-hop-self
neighbor 172.16.254.9 remote-as 10
neighbor 172.16.254.9 next-hop-self
neighbor 172.16.255.5 remote-as 20
neighbor 172.16.255.9 remote-as 30
neighbor 172.16.255.25 remote-as 60
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R3
router bgp 10
no synchronization
aggregate-address 172.16.0.0 255.255.248.0 summary-only
neighbor 172.16.254.5 remote-as 10
neighbor 172.16.254.5 next-hop-self
neighbor 172.16.254.10 remote-as 10
neighbor 172.16.254.10 next-hop-self
neighbor 172.16.255.13 remote-as 40
neighbor 172.16.255.17 remote-as 50
neighbor 172.16.255.21 remote-as 60
neighbor 172.16.255.21 next-hop-self
The objective is to suppress all the more-specific routes and advertise only an aggregate. R8's BGP table, in Example 3-171, still shows the more-specific routes. What is wrong?
Example 3-171 The BGP Table of R8 in Figure 3-37
R8#show ip bgp
BGP table version is 163, local router ID is 172.21.1.1
Status codes: s suppressed, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 172.16.255.18 0 10 i
*> 172.17.0.0 172.16.255.18 0 10 60 i
*> 172.18.0.0 172.16.255.18 0 10 30 i
*> 172.19.0.0 172.16.255.18 0 10 20 i
*> 172.20.0.0 172.16.255.18 0 10 40 i
*> 172.21.0.0 0.0.0.0 0 32768 i
R8#
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| | 6: | Packets from AS 60 destined for any of the other autonomous systems shown in Figure 3-37 should be forwarded across the link between R6 and R1. The link between R7 and R3 should be used only as a backup for this traffic, although packets destined for the Internet can still use this link. To implement this policy, R3 should advertise only the default route and the aggregate 172.16.0.0/13. R1 should advertise the more-specific routes. Example 3-172 shows the configurations for R1, R3, R6, and R7.
Example 3-172 Configurations for Routers R1, R3, R6, and R7
R1
router bgp 10
no synchronization
neighbor 172.16.254.1 remote-as 10
neighbor 172.16.254.1 next-hop-self
neighbor 172.16.254.9 remote-as 10
neighbor 172.16.254.9 next-hop-self
neighbor 172.16.255.5 remote-as 20
neighbor 172.16.255.9 remote-as 30
neighbor 172.16.255.25 remote-as 60
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R3
router bgp 10
no synchronization
aggregate-address 172.16.0.0 255.248.0.0 summary-only
neighbor 172.16.254.5 remote-as 10
neighbor 172.16.254.5 next-hop-self
neighbor 172.16.254.10 remote-as 10
neighbor 172.16.254.10 next-hop-self
neighbor 172.16.255.13 remote-as 40
neighbor 172.16.255.17 remote-as 50
neighbor 172.16.255.21 remote-as 60
neighbor 172.16.255.21 next-hop-self
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R6
redistribute bgp 60 metric 1000 100 255 1 1500
network 172.17.0.0
!
router bgp 60
network 172.17.0.0
neighbor 172.16.255.26 remote-as 10
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R7
router eigrp 60
redistribute bgp 60 metric 1000 100 255 1 1500
network 172.17.0.0
!
router bgp 60
network 172.17.0.0
neighbor 172.16.255.22 remote-as 10
Example 3-173 shows R7's routing table. Has the objective been accomplished? If not, why not?
Example 3-173 R7's Routing Table for Troubleshooting Exercise 6
R7#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
T - traffic engineered route
Gateway of last resort is 172.16.255.22 to network 0.0.0.0
172.17.0.0/24 is subnetted, 3 subnets
C 172.17.1.0 is directly connected, Ethernet0
D 172.17.3.0 [90/409600] via 172.17.1.2, 09:18:50, Ethernet0
C 172.17.2.0 is directly connected, Ethernet1
172.16.0.0/30 is subnetted, 1 subnets
C 172.16.255.20 is directly connected, Serial0
D EX 172.19.0.0/16 [170/2611200] via 172.17.1.2, 00:19:08, Ethernet0
D EX 172.18.0.0/16 [170/2611200] via 172.17.1.2, 00:19:08, Ethernet0
B* 0.0.0.0/0 [20/0] via 172.16.255.22, 00:18:37
B 172.16.0.0/13 [20/0] via 172.16.255.22, 00:18:09
R7#
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| | 7: | Reexamine Figure 3-19 and Example 3-98 and the associated discussion. Meribel advertises its local route 172.17.0.0 to its EBGP peers with an ORIGIN of Incomplete, whereas Lillehammer advertises the route back to Meribel with an ORIGIN of IGP. Will this cause Meribel to prefer the route from Lillehammer, thereby causing a routing loop?
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___________________________________________________________________________ | | 8: | Example 3-174 shows the configuration for the router named Colorado in Figure 3-24.
Example 3-174 Configuration for Router Colorado in Figure 3-24
router bgp 100
network 10.1.11.0 mask 255.255.255.0
network 10.1.12.0 mask 255.255.255.0
neighbor CLIENTS peer-group
neighbor CLIENTS ebgp-multihop 2
neighbor CLIENTS update-source Loopback2
neighbor CLIENTS filter-list 2 in
neighbor CLIENTS filter-list 1 out
neighbor 10.1.255.2 remote-as 200
neighbor 10.1.255.2 peer-group CLIENTS
neighbor 10.1.255.3 remote-as 300
neighbor 10.1.255.3 peer-group CLIENTS
neighbor 10.1.255.4 remote-as 400
neighbor 10.1.255.4 peer-group CLIENTS
neighbor 10.1.255.5 remote-as 500
neighbor 10.1.255.5 peer-group CLIENTS
neighbor 10.1.255.6 remote-as 600
neighbor 10.1.255.6 peer-group CLIENTS
no auto-summary
!
ip classless
ip route 10.1.255.2 255.255.255.255 Serial0/1.305
ip route 10.1.255.3 255.255.255.255 Serial0/1.306
ip route 10.1.255.4 255.255.255.255 Serial0/1.307
ip route 10.1.255.5 255.255.255.255 Serial0/1.308
!
ip as-path access-list 1 permit ^$
ip as-path access-list 2 permit ^[2-6]00$
All router IDs shown in Figure 3-24 are configured on loopback interfaces, and no routing protocol other than BGP is running on any of the routers. Assuming that all the links shown in the figure are functioning properly, are all the other five routers EBGP peers of Colorado? If not, why not?
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___________________________________________________________________________ | | 9: | Refer to the configuration shown in Troubleshooting Exercise 8 for router Colorado in Figure 3-24. What will be the result of removing the no auto-summary statement from the configuration?
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| | 10: | Refer again to the configuration shown in Troubleshooting Exercise 8. What routes does the incoming route filter permit?
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___________________________________________________________________________ | | 11: | Refer to Figure 3-24 and the configuration for router Colorado in Troubleshooting Exercise 8. What subnets, other than those local to its own AS or the inter-AS links, can a host on subnet 10.1.3.0/24 ping?
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