- Topic: Describe DNS lookup operation
- Topic: Troubleshoot client connectivity issues involving DNS
- Topic: Configure and verify DHCP on a router (excluding static reservations)
- Topic: Troubleshoot client- and router-based DHCP connectivity issues
- Topic: Configure and verify NTP operating in client/server mode
- Topic: Configure, verify, and troubleshoot basic HSRP
- Review Questions
- Answers to Review Questions
- Additional Resources
This chapter is from the book
This chapter is from the book
This chapter is from the book
Topic: Troubleshoot client- and router-based DHCP connectivity issues
CramSaver
Examine the figure and the example configurations. Why is the DHCP client failing to acquire IP address information?
What command allows you to easily verify the lease assignments from the DHCP server?
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R1# R1#show running-config Building configuration... Current configuration : 1343 bytes ! ! Last configuration change at 08:30:24 UTC Fri Aug 26 2016 ! upgrade fpd auto version 15.0 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R1 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! ! ! ip source-route no ip icmp rate-limit unreachable ip cef ! ! ip dhcp excluded-address 10.1.1.1 10.1.1.10 ! ip dhcp pool CCNAEXAMCRAM network 10.1.2.0 255.255.255.0 default-router 10.1.1.1 dns-server 8.8.8.8 4.2.2.2 option 150 ip 10.10.10.2 ! ! no ip domain lookup no ipv6 cef ! multilink bundle-name authenticated ! ! ! redundancy ! ! ip tcp synwait-time 5 ! ! ! interface FastEthernet0/0 ip address 10.1.1.1 255.255.255.0 duplex half ! ! interface FastEthernet1/0 no ip address shutdown duplex auto speed auto ! ! interface FastEthernet1/1 no ip address shutdown duplex auto speed auto ! ! ip forward-protocol nd no ip http server no ip http secure-server ! ! ! no cdp log mismatch duplex ! ! ! control-plane ! ! ! mgcp fax t38 ecm mgcp behavior g729-variants static-pt ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line vty 0 4 login ! ntp master 2 end R1# R2# R2#show running-config Building configuration... Current configuration : 1165 bytes ! ! Last configuration change at 08:49:30 UTC Fri Aug 26 2016 ! upgrade fpd auto version 15.0 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R2 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! ! ! ip source-route no ip icmp rate-limit unreachable ip cef ! ! ! no ip domain lookup no ipv6 cef ! multilink bundle-name authenticated ! ! ! redundancy ! ! ip tcp synwait-time 5 ! ! ! interface FastEthernet0/0 ip address dhcp duplex half ! ! interface FastEthernet1/0 no ip address shutdown duplex auto speed auto ! ! interface FastEthernet1/1 no ip address shutdown duplex auto speed auto ! ! ip forward-protocol nd no ip http server no ip http secure-server ! ! ! no cdp log mismatch duplex ! ! ! control-plane ! ! ! mgcp fax t38 ecm mgcp behavior g729-variants static-pt ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line vty 0 4 login ! ntp server 10.1.1.1 end R2#
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Answers
The subnet for lease assignments is incorrect for the DHCP server pool; the correct subnet should be configured with network 10.1.1.0 /24.
show ip dhcp server bindings
There can be many issues to prevent proper DHCP connectivity. Here are just some issues you should be aware of:
Errors in router or switch configurations
DHCP server configuration
DHCP relay-agent configuration
DHCP server scope configuration or software defect
The four steps of the DHCP process that must succeed for a successful DHCP lease are as follows:
Discover (from the client)
Offer (from the server)
Request (from the client)
Acknowledgement (from the server)
Remember the key verification commands for DHCP. show ip dhcp binding is critical for the server, and show ip interface brief works well for the client.
CramQuiz
Examine the configuration shown. DHCP clients in the 10.1.1.0/24 subnet are complaining that they cannot access Internet resources. What is the most likely issue?
A. The scope of addresses in the pool is not correct.- B. There is no lease duration set.
- C. There are no DNS servers assigned to the clients.
- D. The default gateway is incorrect.
What is the second step of the four steps of the DHCP process?
- A. Acknowledgement
- B. Request
- C. Offer
- D. Discover
R1#show running-config Building configuration... Current configuration : 1312 bytes ! ! Last configuration change at 08:57:10 UTC Fri Aug 26 2016 ! upgrade fpd auto version 15.0 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R1 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! ! ! ip source-route no ip icmp rate-limit unreachable ip cef ! ! ip dhcp excluded-address 10.1.1.1 10.1.1.10 ! ip dhcp pool CCNAEXAMCRAM network 10.1.1.0 255.255.255.0 default-router 10.1.1.1 option 150 ip 10.10.10.2 ! ! no ip domain lookup no ipv6 cef ! multilink bundle-name authenticated ! ! redundancy ! ! ip tcp synwait-time 5 ! ! ! interface FastEthernet0/0 ip address 10.1.1.1 255.255.255.0 duplex half ! ! interface FastEthernet1/0 no ip address shutdown duplex auto speed auto ! ! interface FastEthernet1/1 no ip address shutdown duplex auto speed auto ! ! ip forward-protocol nd no ip http server no ip http secure-server ! ! ! no cdp log mismatch duplex ! ! ! control-plane ! ! ! mgcp fax t38 ecm mgcp behavior g729-variants static-pt ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line vty 0 4 login ! ntp master 2 end R1#
CramQuiz Answers
C is correct. This configuration is missing the assignment of DNS servers for the clients.
C is correct. The second step of the process is an offer.
