- Scenario: Shooting Trouble with IP
- Protocols and Packets
- Addressing
- Routing Protocols
- Trouble Tickets
- Trouble Tickets Solutions
- Review Questions
- Summary
This chapter is from the book
This chapter is from the book
This chapter is from the book
Trouble Tickets Solutions
These solutions are not always the only way to perform these tasks. However, the upcoming chapter scenarios are based on these solutions.
Trouble Ticket 1 Solution
I reviewed and copied my existing configurations to my TFTP server as rx-rip2, where I replaced x for each router number. In Example 3-37, I performed a simple ping first to make sure I had connectivity to the TFTP server, and then copied the files. You may want to tweak the configuration of your TFTP server to place the files in the location you prefer for easy access later. You should also get familiar with how your particular TFTP server handles files that already exist. For example, you may want to have it prompt you as to what to do if the files already exist. The answer shows the output for r1 only, but this was performed from each router.
Example 3-37 Copying Existing Configurations to a TFTP Server
r1#ping 192.168.1.11 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.1.11, timeout is 2 seconds: .!!!! Success rate is 80 percent (4/5), round-trip min/avg/max = 1/3/4 ms r1#copy running-config tftp Address or name of remote host []? 192.168.1.11 Destination filename [running-config]? r1-rip2 !! 1169 bytes copied in 5.680 secs (233 bytes/sec) r1#
Trouble Ticket 2 Solution
Figure 3-34 displays the new addressing scheme that I used as a guide for configurations in the examples to follow.
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Figure
3-34 Trouble Tickets Scenario
Trouble Ticket 3 Solution
I used Figure 3-34 as a guide to re-address the network. Example 3-38 shows a few problems I had when re-addressing the interfaces. I could have typed no ip address on each interface to remove the old one before I started, but then you may not have realized the overlapping problems. While on each router, I also issued no router rip to quickly remove the RIP routing protocol commands. A quick test after the configuration is to perform show ip interface brief to verify the configuration against the drawing.
NOTE
Although I did not shut my interfaces down before and after configuring them, that is certainly the best practice to do so.
Example 3-38 Re-Addressing and Removing RIP
r1(config)#interface e0 r1(config-if)#ip address 192.168.5.17 255.255.255.240 r1(config-if)#interface e1 r1(config-if)#ip address 192.168.5.33 255.255.255.240 r1(config-if)#interface s1 r1(config-if)#ip add 192.168.5.81 255.255.255.240 r1(config-if)#no router rip r1(config)#end r1#copy running-config startup-config r2(config)#interface e0 r2(config-if)#ip address 192.168.5.34 255.255.255.240 192.168.5.32 overlaps with Serial1 r2(config-if)#interface s1 r2(config-if)#ip address 192.168.5.49 255.255.255.240 r2(config-if)#interface e0 r2(config-if)#ip address 192.168.5.34 255.255.255.240 r2(config-if)#interface s0 r2(config-if)#ip address 192.168.5.65 255.255.255.240 r2(config-if)#no router rip r2(config)#end r2#copy running-config startup-config r3(config)#interface s0/0 r3(config-if)#ip address 192.168.5.82 255.255.255.240 192.168.5.80 overlaps with Serial0/2 r3(config-if)#interface s0/2 r3(config-if)#ip address 192.168.5.50 255.255.255.0 r3(config-if)#interface s0/0 r3(config-if)#ip address 192.168.5.82 255.255.255.240 192.168.5.80 overlaps with Serial0/2 r3(config-if)#interface s0/2 r3(config-if)#ip address 192.168.5.50 255.255.255.240 r3(config-if)#interface s0/0 r3(config-if)#ip address 192.168.5.82 255.255.255.240 r3(config-if)#interface s0/1 r3(config-if)#ip address 192.168.5.66 255.255.255.240 r3(config-if)#interface fa2/0 r3(config-if)#ip address 192.168.5.97 255.255.255.240 r3(config-if)#no router rip r3(config)#end r3#copy running-config startup-config r4(config)#no router rip r4(config)#end r4#copy running-config startup-config r5(config)#no router rip r5(config)#end r5#copy running-config startup-config r1#show ip interface brief Interface IP-Address OK? Method Status Protocol Ethernet0 192.168.5.17 YES manual up up Ethernet1 192.168.5.33 YES manual up up Serial0 10.1.1.1 YES NVRAM up up Serial1 192.168.5.81 YES manual up up r2#show ip interface brief Interface IP-Address OK? Method Status Protocol Ethernet0 192.168.5.34 YES manual up up Serial0 192.168.5.65 YES manual up up Serial1 192.168.5.49 YES manual up up r3#show ip interface brief Interface IP-Address OK? Method Status Protocol Serial0/0 192.168.5.82 YES manual up up Serial0/1 192.168.5.66 YES manual up up Serial0/2 192.168.5.50 YES manual up up Serial0/3 10.2.2.1 YES NVRAM up up ... FastEthernet2/0 192.168.5.97 YES manual up up
Trouble Ticket 4 Solution
Example 3-39 starts the EIGRP configuration and testing. I used AS number 500 for my test and saved my configurations as I went along. Notice in Example 3-39 how I configured 10.1.1.0 and 10.2.2.0. show running-config shows 10.0.0.0. EIGRP is relatively easy to configure, but remember that it is proprietary.
Example 3-39 EIGRP Configuration
r1(config)#router eigrp 500 r1(config-router)#network 192.168.5.0 r1(config-router)#network 10.1.1.0 r1(config-router)#end r1#copy running-config startup-config r2(config)#router eigrp 500 r2(config-router)#network 192.168.5.0 r2(config-router)#end r2#copy running-config startup-config r3(config)#router eigrp 500 r3(config-router)#network 192.168.5.0 r3(config-router)#network 10.2.2.0 r3(config-router)#end r3#copy running-config startup-config r4(config)#router eigrp 500 r4(config-router)#network 10.2.2.0 r4(config-router)#end r4#copy running-config startup-config r5(config)#router eigrp 500 r5(config-router)#network 10.1.1.0 r5(config-router)#end r5#copy running-config startup-config r5#show running-config ... router eigrp 500 network 10.0.0.0 ! ip classless ! ... end
Example 3-40 illustrates show ip protocols and show ip route to verify EIGRP parameters and routes. You should verify every router; I have listed only the first one. The EIGRP learned routes are shown with a D, whereas RIP represented them with an R. It is important to note how EIGRP automatically summarizes on the classful boundary.
Example 3-40 EIGRP Testing with show ip protocols and show ip route
r1>show ip protocols
Routing Protocol is "eigrp 500"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 500
Automatic network summarization is in effect
Automatic address summarization:
10.0.0.0/8 for Ethernet0, Ethernet1, Serial1
Summarizing with metric 40512000
192.168.5.0/24 for Serial0
Summarizing with metric 281600
Routing for Networks:
10.0.0.0
192.168.5.0
Routing Information Sources:
Gateway Distance Last Update
(this router) 5 00:16:31
10.1.1.2 90 00:15:44
192.168.5.82 90 00:16:31
Gateway Distance Last Update
192.168.5.34 90 00:16:32
Distance: internal 90 external 170
r1>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
Gateway of last resort is not set
192.168.5.0/24 is variably subnetted, 7 subnets, 2 masks
D 192.168.5.96/28 [90/40514560] via 192.168.5.82, 00:16:37, Serial1
D 192.168.5.64/28 [90/40537600] via 192.168.5.34, 00:16:37, Ethernet1
C 192.168.5.80/28 is directly connected, Serial1
C 192.168.5.32/28 is directly connected, Ethernet1
D 192.168.5.48/28 [90/40537600] via 192.168.5.34, 00:16:37, Ethernet1
D 192.168.5.0/24 is a summary, 00:18:11, Null0
C 192.168.5.16/28 is directly connected, Ethernet0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.0.0.0/8 is a summary, 00:16:37, Null0
C 10.1.1.0/24 is directly connected, Serial0
NOTE
Think about the routing table issues as you work through some common EIGRP troubleshooting commands.
Example 3-41 further explores EIGRP with some EIGRP-specific IOS debug commands. I disconnected the r1S1 cable after turning on a pretty explicit command for you to see the EIGRP packet and update process. After looking at the routing table, I plugged the cable back in and explored some of the EIGRP show and logging commands that are quite helpful in troubleshooting in Example 3-42.
Example 3-41 Experimenting with EIGRP Troubleshooting Tools
r1#debug eigrp ? fsm EIGRP Dual Finite State Machine events/actions neighbors EIGRP neighbors packets EIGRP packets transmit EIGRP transmission events r1#debug eigrp transmit EIGRP Transmission Events debugging is on (ACK, PACKETIZE, STARTUP, PEERDOWN, LINK, BUILD, STRANGE, DETAIL) 01:21:06: %LINK-3-UPDOWN: Interface Serial1, changed state to down 01:21:06: DNDB QUERY 192.168.5.80/28, serno 3 to 16, refcount 3 01:21:06: Anchoring Serial0, starting Serial0 timer 01:21:06: Anchoring Ethernet1, starting Ethernet1 timer 01:21:06: Anchoring Serial1, starting Serial1 timer 01:21:06: Peer 192.168.5.82 going down 01:21:06: DNDB QUERY 192.168.5.96/28, serno 15 to 17, refcount 3 01:21:06: Last peer deleted from Serial1 01:21:06: Dropping refcount on 192.168.5.80/28, refcount now 2 01:21:06: Dropping refcount on 192.168.5.96/28, refcount now 2 01:21:06: Packetizing timer expired on Serial0 01:21:06: Packets pending on Serial0 01:21:06: Intf Serial0 packetized QUERY 16-17 01:21:06: Interface is now quiescent 01:21:06: Building multicast QUERY packet for Serial0, serno 16-17 01:21:06: Items: U16 U17 01:21:06: Packetizing timer expired on Ethernet1 01:21:06: Packets pending on Ethernet1 01:21:06: Intf Ethernet1 packetized QUERY 16-17 01:21:06: Interface is now quiescent 01:21:06: Building multicast QUERY packet for Ethernet1, serno 16-17 01:21:06: Items: 16 17 01:21:06: Packetizing timer expired on Serial1 01:21:06: Packet acked from 192.168.5.34 (Ethernet1), serno 16-17 01:21:06: Flow blocking cleared on Ethernet1 01:21:06: Multicast acked from Ethernet1, serno 16-17 01:21:06: Found serno 16, refcount now 1 01:21:06: Found serno 17, refcount now 1 01:21:06: Packet acked from 10.1.1.2 (Serial0), serno 16-17 01:21:06: Flow blocking cleared on Serial0 ... 01:21:07: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down r1#show ip route ... 192.168.5.0/24 is variably subnetted, 6 subnets, 2 masks D 192.168.5.96/28 [90/40540160] via 192.168.5.34, 00:00:12, Ethernet1 D 192.168.5.64/28 [90/40537600] via 192.168.5.34, 00:32:10, Ethernet1 C 192.168.5.32/28 is directly connected, Ethernet1 D 192.168.5.48/28 [90/40537600] via 192.168.5.34, 00:32:10, Ethernet1 D 192.168.5.0/24 is a summary, 00:33:44, Null0 C 192.168.5.16/28 is directly connected, Ethernet0 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.0.0.0/8 is a summary, 00:32:11, Null0 C 10.1.1.0/24 is directly connected, Serial0 01:21:38: %LINK-3-UPDOWN: Interface Serial1, changed state to up 01:21:38: DNDB UPDATE 192.168.5.80/28, serno 0 to 20, refcount 2 01:21:38: Anchoring Serial0, starting Serial0 timer 01:21:38: Anchoring Ethernet1, starting Ethernet1 timer 01:21:38: Packetizing timer expired on Serial0 01:21:38: Packets pending on Serial0 01:21:38: Intf Serial0 packetized UPDATE 20-20 01:21:38: Interface is now quiescent 01:21:38: Building multicast UPDATE packet for Serial0, serno 20-20 01:21:38: Items: S20 01:21:38: Suppressed. ... 01:21:38: Building startup packet for 192.168.5.82, serno 1-20 01:21:38: Items: 1 2 S4 S5 6 7 8 19 S20 01:21:39: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up 01:21:40: Building startup packet for 192.168.5.82, serno 1-20 01:21:40: Items: 1 2 S4 S5 6 7 8 19 S20 01:21:42: DNDB UPDATE 192.168.5.96/28, serno 19 to 21, refcount 3 01:21:42: Anchoring Serial1, starting Serial1 timer 01:21:42: Anchoring Ethernet1, starting Ethernet1 timer 01:21:42: Anchoring Serial0, starting Serial0 timer 01:21:42: Packetizing timer expired on Serial1 01:21:42: Packets pending on Serial1 01:21:42: Intf Serial1 packetized UPDATE 21-21 r1#show ip route ... 192.168.5.0/24 is variably subnetted, 7 subnets, 2 masks D 192.168.5.96/28 [90/40514560] via 192.168.5.82, 00:00:04, Serial1 D 192.168.5.64/28 [90/40537600] via 192.168.5.34, 00:00:04, Ethernet1 C 192.168.5.80/28 is directly connected, Serial1 C 192.168.5.32/28 is directly connected, Ethernet1 D 192.168.5.48/28 [90/40537600] via 192.168.5.34, 00:00:04, Ethernet1 D 192.168.5.0/24 is a summary, 00:34:12, Null0 C 192.168.5.16/28 is directly connected, Ethernet0 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.0.0.0/8 is a summary, 00:00:04, Null0 C 10.1.1.0/24 is directly connected, Serial0 r1#undebug all
Example 3-42 Troubleshooting Using EIGRP Show Commands
r1#show ip eigrp ?
interfaces IP-EIGRP interfaces
neighbors IP-EIGRP neighbors
topology IP-EIGRP Topology Table
traffic IP-EIGRP Traffic Statistics
r1#show ip eigrp neighbors
IP-EIGRP neighbors for process 500
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 192.168.5.82 Se1 12 00:01:15 24 2280 0 38
2 10.1.1.2 Se0 14 00:33:05 44 2280 0 3
0 192.168.5.34 Et1 10 00:34:23 25 200 0 35
r1#show ip eigrp interfaces
IP-EIGRP interfaces for process 500
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Et0 0 0/0 0 0/10 0 0
Et1 1 0/0 25 0/10 108 0
Se1 1 0/0 24 10/380 380 0
Se0 1 0/0 44 10/380 556 0
r1#show ip eigrp topology ?
<1-65535> AS Number
A.B.C.D Network to display information about
active Show only active entries
all-links Show all links in topology table
pending Show only entries pending transmission
summary Show a summary of the topology table
zero-successors Show only zero successor entries
<cr>
r1#show ip eigrp topology active
IP-EIGRP Topology Table for process 500
The next two commands are very useful for EIGRP troubleshooting. Turn them on and note the output (as I do in Example 3-43). To force some changes, I issued a no shut on r1s1 to see a neighbor change. I brought that interface back up, turned off the neighbor changes, and turned on the neighbor warnings. Then I went to r2 to bounce (shut/no shut) the Ethernet 0 interface to observe the results.
Example 3-43 EIGRP Logging
r1(config)#router eigrp 500 r1(config-router)#eigrp ? log-neighbor-changes Enable/Disable IP-EIGRP neighbor logging log-neighbor-warnings Enable/Disable IP-EIGRP neighbor warnings r1(config-router)#eigrp log-neighbor-changes r1(config-router)#end ... r1(config)#interface s1 r1(config-if)#shut 01:42:34: %DUAL-5-NBRCHANGE: IP-EIGRP 500: Neighbor 192.168.5.82 (Serial1) is down: interface down 01:42:36: %LINK-5-CHANGED: Interface Serial1, changed state to administratively down 01:42:37: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down r1(config-if)#no shut 01:42:54: %LINK-3-UPDOWN: Interface Serial1, changed state to up 01:42:55: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up 01:42:56: %DUAL-5-NBRCHANGE: IP-EIGRP 500: Neighbor 192.168.5.82 (Serial1) is up: new adjacency r1(config-if)#exit r1(config)#router eigrp 500 r1(config-router)#no eigrp log-neighbor-changes r1(config-router)#eigrp log-neighbor-warnings r1(config-router)#exit r1(config)#interface s1 r1(config-if)#shut 01:43:33: %DUAL-5-NBRCHANGE: IP-EIGRP 500: Neighbor 192.168.5.82 (Serial1) is down: interface down 01:43:35: %LINK-5-CHANGED: Interface Serial1, changed state to administratively down 01:43:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down r1(config-if)#no shut r2(config)#interface e0 r2(config-if)#shut r1 01:44:30: %DUAL-5-NBRCHANGE: IP-EIGRP 500: Neighbor 192.168.5.34 (Ethernet1) is down: holding time expired r2(config-if)#no shut r1 01:44:55: %DUAL-5-NBRCHANGE: IP-EIGRP 500: Neighbor 192.168.5.34 (Ethernet1) is up: new adjacency
Look back through the examples and compare the output of some of the commands to your drawing. There are still issues with EIGRP. Can you spot them? Fix them and continue on to the next Trouble Ticket.
A simple ping test or looking at the routing tables for network 10.0.0.0 should have told you that EIGRP automatically summarizes on the classful boundary. On r1 and r5, for example, you could see 10.1.1.0 but not 10.2.2.0. r3 and r4 displayed 10.2.2.0, but not 10.1.1.0. The fix is in Example 3-44, and the commands are required on r1 and on r3 since they cross network boundaries. Test by displaying the routing table on r2 and ping testing from router to router, although a better test would be from hosta to 10.2.2.2.
Example 3-44 EIGRP no auto-summary Fix
r2#show ip route
192.168.5.0/28 is subnetted, 6 subnets
D 192.168.5.96 [90/40514560] via 192.168.5.66, 00:03:35, Serial0
[90/40514560] via 192.168.5.50, 00:03:35, Serial1
C 192.168.5.64 is directly connected, Serial0
D 192.168.5.80 [90/40537600] via 192.168.5.33, 00:03:36, Ethernet0
C 192.168.5.32 is directly connected, Ethernet0
C 192.168.5.48 is directly connected, Serial1
D 192.168.5.16 [90/307200] via 192.168.5.33, 00:03:36, Ethernet0
D 10.0.0.0/8 [90/40537600] via 192.168.5.33, 00:03:36, Ethernet0
r1(config)#router eigrp 500
r1(config-router)#no auto-summary
r1(config-router)#end
r1#copy running-config startup-config
r3(config)#router eigrp 500
r3(config-router)#no auto-summary
r3(config-router)#end
r3#copy running-config startup-config
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
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
Gateway of last resort is not set
192.168.5.0/28 is subnetted, 6 subnets
D 192.168.5.96 [90/40514560] via 192.168.5.66, 00:00:50, Serial0
[90/40514560] via 192.168.5.50, 00:00:50, Serial1
C 192.168.5.64 is directly connected, Serial0
D 192.168.5.80 [90/40537600] via 192.168.5.33, 00:00:50, Ethernet0
C 192.168.5.32 is directly connected, Ethernet0
C 192.168.5.48 is directly connected, Serial1
D 192.168.5.16 [90/307200] via 192.168.5.33, 00:00:50, Ethernet0
10.0.0.0/24 is subnetted, 2 subnets
D 10.2.2.0 [90/41024000] via 192.168.5.66, 00:00:50, Serial0
[90/41024000] via 192.168.5.50, 00:00:50, Serial1
D 10.1.1.0 [90/40537600] via 192.168.5.33, 00:00:51, Ethernet0
r2>
Notice how the 10.1.1.0 and 10.2.2.0 subnets now display in the routing table with a D in front. Just as with the previous RIPv2 examples, the no auto-summary command is critical in a situation such as this in order for EIGRP to support discontiguous subnets. EIGRP enables you to summarize manually on any boundary and interface you so choose.
Trouble Ticket 5 Solution
You should now be able to successfully ping and trace between all your routers. That is great, but the real goal is host-to-host, end-to-end connectivity. See whether you can ping and tracert from hosta to hostc and capture the results. Of course, if you are like me, you may have forgotten to change the IP address information on your hosts. Obviously that is a prerequisite to the rest of this. Table 3-12 shows my host parameters. If you need more help with addresses, masks, and gateways, experiment a little more here by changing one at the time and observing the results. Practice does make perfect! Compare your results to my output in Example 3-45 and Figure 3-35. Also take time to examine how Sniffer displays EIGRP. Remember to save all your configuration files to the TFTP server with the rx-eigrp name format.
)
Figure
3-35 EIGRP and Client Initialization Traffic
Table 3-12 Trouble Ticket Host Configuration
|
|
IP Address |
Subnet Mask |
Gateway |
|
hosta |
192.168.5.18 |
255.255.255.240 |
192.168.5.17 |
|
hostb |
192.168.5.19 |
255.255.255.240 |
192.168.5.17 |
|
hostc |
192.168.5.98 |
255.255.255.240 |
192.168.5.97 |
Example 3-45 Trouble Ticket 5 Ping and Trace Output
C:\>ping 192.168.5.98 Pinging 192.168.5.98 with 32 bytes of data: Request timed out. Reply from 192.168.5.98: bytes=32 time=20ms TTL=126 Reply from 192.168.5.98: bytes=32 time=10ms TTL=126 Reply from 192.168.5.98: bytes=32 time=10ms TTL=126 Ping statistics for 192.168.5.98: Packets: Sent = 4, Received = 3, Lost = 1 (25% loss), Approximate round trip times in milli-seconds: Minimum = 10ms, Maximum = 20ms, Average = 10ms C:\>tracert 192.168.5.98 Tracing route to HOSTC [192.168.5.98] over a maximum of 30 hops: 1 <10 ms 10 ms <10 ms 192.168.5.17 2 20 ms 20 ms 20 ms 192.168.5.82 3 20 ms 30 ms 30 ms HOSTC [192.168.5.98] Trace complete.
I captured my file just after I made the change to the hostb IP changes. I started Sniffer upon bootup to capture the Windows 98 client bootup for later review. The file is chapter 3 eigrp and client initialization traffic sniffer capture.
The first couple of hundred lines of the Sniffer capture include hostb booting up to the Windows 98 operating system. Starting in line 221, I issued a ping and then a tracert from hosta to hostc as the output in Example 3-45 depicts. See the EIGRP multicast 224.0.0.10 hello address and IP handing off to EIGRP over protocol number 88.
You have completed the chapter Trouble Tickets when you feel comfortable with the tasks assigned and the various scenarios throughout the chapter. I saved my configurations to the TFTP server and also logged the output of show running-config to a file. I did not bother with changing the hosts files, but you certainly can if you so desire. However, I will have you write erase in the next chapter anyway.
Review or experiment in the areas where you need more help. Understanding and troubleshooting in a simple environment is certainly the foundation for understanding and troubleshooting complex protocols and technologies. Check your understanding with the chapter review questions.