Uplink Fast is a Cisco proprietary feature to increase the convergence time for the STP when a failure is detected and to provide load balancing over the redundant paths. It is only useful when redundant connections are used and therefore should never be configured on a port that is connected directly to a switch or a server (if there are multiple links, Fast EtherChannel should be used).
Figure 7-6 shows a redundant configuration. The four switches are connected together via four uplink ports. If all ports were configured for Uplink Fast and U1 were to fail, the blocking path, U2, would be placed in the forwarding state without passing through the listening and learning states, thus increasing the recovery time. According to the Cisco documentation, this usually occurs within 5 seconds (Figure 7-7).
The proper syntax for configuring Uplink Fast is
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Figure 7-6 Uplink Fast Connection
Cat5000> (enable) set spantree uplinkfast enable VLANs 1-1005 bridge priority set to 49152.
The port cost and portvlancost of all ports set to above 3000.
Station update rate set to 15 packets/100ms.
uplinkfast all-protocols field set to off.
uplinkfast enabled for bridge.
Cat5000> (enable)
There is no way to configure Uplink Fast on only a single port. Uplink Fast sets the bridge priority and port costs to extremely large values to reduce the chances that they will be selected as the root bridge. This configuration is only recommended in the wiring closet by Cisco Systems.
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Figure 7-7 A Failure Occurs in U1
Summary
The Cisco Catalyst command line interface (CLI) was designed to look and feel like the true Cisco IOS, but it has many differences. This chapter explored working with the CLI. The one interesting difference between the Cisco IOS and the Catalyst IOS is the Catalyst IOS's use of the set command rather than the configuration modes of Cisco IOS. The configuration file also is very large compared with that of a router.
The architecture of a Catalyst switch also resembles that of a Cisco Router. Flash memory, NVRAM, and RAM serve basically the same
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purpose on Catalyst switches that they do on a Cisco router. This chapter examined the commands to work with these areas of memory.
Management of a switch can be achieved through use of an SNMP management server or the CLI. The CLI can be accessed via the console port or through the IP application Telnet. The interface sc0 is a virtual interface configured on the switch to allow IP connectivity for SNMP or Telnet access to the switch. Remote access via a POTS line can be achieved through use of interface sl0.
Security of a switch is controlled by two passwords. The user mode password is necessary to log in to user mode, whereas the privileged mode or enable password is necessary to log in to privileged mode or enable mode (that was simple!). Additional security can be created by using an IP permit list (not an access list).
The Spanning Tree Protocol (STP) can be difficult to manage when there are many VLANs configured on a switch. With one STP per VLAN, it is recommended to keep the STP customization to a minimum to prevent unwanted administrative overhead. The Portfast and Uplink Fast features of the switch can reduce the length of time it takes a port to go into the forwarding mode.
Exercises
1. Describe the requirements for a Catalyst switch to perform a RARP or BOOTP to resolve its IP address during the boot procedure.
2. What password(s) is(are) required to log into a switch and view parameters? What mode is this called?
3. What password(s) is(are) required to log into a switch and change the configuration file? What mode is this called? What is(are) the command(s) to configure these password(s)?
4. Why must one type quickly to perform password recovery? What shortcuts can you think of to speed password recovery?
5. Why is it suggested that the SNMP parameters be changed from the default values?
6. Why is it suggested that only the default gateway be configured as opposed to individual routes? What is the command to configure the default gateway of a switch to 172.16.1.64 255.255.255.192?
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7. Given the following output, what is the MAC address that will be used by this switch when performing a RARP or BOOTP?
Cat5000> (enable) sh module
Mod Module-Name u
Mod Sub-Type Sub-Model Sub-Serial Sub-Hw ––– –––––––– ––––––––– –––––––––– –––––––
1 1 + WS-F5520 1 Cat5000> (enable)
8. What is the alternative to using a DNS server to resolve addresses on a Catalyst switch?
9. In what area of memory is the configuration file of a Catalyst switch stored? What is the command to copy the configuration file from RAM to NVRAM?
10. Why are the ATM ports not configured on the CLI of a Catalyst switch?
Serial-Num Stat
24 10/100BaseTX Ethernet WS-X5224 010907441 ok 24 100BaseFX MM Ethernet WS-X5201R 009976930 ok 12
00-10-7b-e9-83-e8 to 00-10-7b-e9-83-ff 3.1(1) 4.3(1a) 4.3(1a)
11. Describe the differences between the flash memory areas of a supervisor engine I or II
compared with a supervisor engine III? What are the different memory areas called, and where do they reside physically?
12. Why is it important to configure a port name on a Catalyst switch? What is the command to name a port?
13. What are the default costs of Ethernet, Fast Ethernet, Gigabit Ethernet, FDDI, and 16-Mb/s Token Ring ports (your answer should be based on the typical method)?
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14. Given the following configuration commands:
Cat5000> (enable) set port speed 1/1 100 Cat5000> (enable) set port duplex 3/1 auto
what duplex method will be used by the 3/1 port? What speed will be used by the 3/1 port?
15. What is the difference between the set spantree portcost command and the set
spantree portvlancost command? What is the difference between the set spantree priority command and the set spantree portvlan priority command?
16. What is the default STP priority of a port? What does it mean?
17. Why is the set spantree portfast command used only with connections to servers, workstations, and routers, not hubs or switches?
18. What are the advantages and disadvantages to using Uplink Fast?
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