Simple Mail Transfer Protocol 127

The following example disables all versions of SNMP:

R1(config)# no snmp-server

The following example enables the router to send all traps to the host, host.cisco.com, using the community string public:

R1(config)# snmp-server enable traps

R1(config)# snmp-server host host.cisco.com public

In the following example, the BGP traps are enabled for all hosts, but only the ISDN traps are enabled to be sent to an actual host named simon:

R1(config)# snmp-server enable traps bgp

R1(config)# snmp-server host simon public isdn

The following example enables the router to send all inform requests to the host test.cisco.com using the community string publiC:

R1(config)# snmp-server enable traps

R1(config)# snmp-server host test.cisco.com informs publiC

Simple Mail Transfer Protocol

128 Chapter 3: Application Protocols

MAIL (MAIL)—Initiates a mail transaction in which the mail data is delivered to mailboxes.

RECIPIENT (RCPT)—Identifies an individual recipient of the mail data; multiple use of the command is needed for multiple users.

DATA (DATA)—The lines following the command are the mail data in ASCII character codes.

SEND (SEND)—Initiates a mail transaction in which the mail data is delivered to one or more terminals.

SEND OR MAIL (SOML)—Initiates a mail transaction in which the mail data is delivered to one or more terminals or mailboxes.

SEND AND MAIL (SAML)—Initiates a mail transaction in which the mail data is delivered to one or more terminals and mailboxes.

RESET (RSET)—The current mail transaction is to be aborted. Any stored sender, recipients, and mail data must be discarded, and all buffers and state tables cleared. The receiver must send an OK reply.

VERIFY (VRFY)—This is to verify if a user exists; a fully specified mailbox and name are returned.

NOOP (NOOP)—Specifies no action other than that the receiver sent an OK reply.

QUIT (QUIT)—The receiver must send an OK reply and then close the transmission channel.

Network Time Protocol

Network Time Protocol (NTP) is used for accurate time keeping and can reference atomic clocks that are present on the Internet, for example. NTP is capable of synchronizing clocks within milliseconds and is a useful protocol when reporting error logs (for instance, from Cisco routers).

For NTP, the defined ports are UDP port 123 and TCP 123. NTP can support a connectionorientated server (TCP guarantees delivery) or connectionless (UDP for non-critical applications).

An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of one another.

NOTE NTP uses the concept of a stratum to describe how many NTP hops away a machine is from an authoritative time source. A stratum 1 time server has a radio or atomic clock directly attached; a stratum 2 time server receives its time via NTP from a stratum 1 time server, and so on. Cisco routers cannot support stratum 1 (in other words, you cannot connect a Cisco router to an atomic clock source) and need to derive an atomic clock source from the Internet. NTP can also authenticate sessions.

130 Chapter 3: Application Protocols

To ensure that R1 sends R2 a clock source via NTP, R1 must be configured to send NTP traffic over the Frame Relay cloud with the command ntp broadcast. To specify that a specific interface should send NTP broadcast packets, use the ntp broadcast interface configuration command. Similarly, R2 must receive NTP traffic and is considered an NTP client with the IOS command ntp broadcast client.

R2’s Serial 0/0 interface is configured with the command ntp broadcast client.

Example 3-8 configures Router R1 in Figure 3-7 to supply a clock source to Router R2.

Example 3-8 NTP Configuration on R1

clock set 10:20:00 9 August 2002 clock timezone UTC 10 !Interface configuration interface serial0/0

ntp broadcast

!Global configuration

ntp authentication-key 1 md5 121A061E17 7 ntp authenticate

ntp trusted-key 1 ntp master 2

ntp peer 131.108.2.1 key 1

Notice that the router is set to the correct time first with the IOS command clock set.

The router is configured for the UTC time zone and 10 hours behind UTC time. The authentication key is set to 1.

Example 3-9 configures R2 to get the clock from R1 using the same MD5 password (set to ccie) from Example 3-8.

Network Time Protocol 131

Example 3-9 NTP Configuration on R2

interface serial0/0 ntp broadcast client !Global configuration

ntp authentication-key 1 md5 ccie ntp authenticate

ntp trusted-key 1 ntp trusted-key

ntp peer 131.108.1.1 key 1

Example 3-10 displays the two clocks on Routers R1 and R2 confirming that R1 is sending R2 the correct time via NTP.

Example 3-10 show clock on R1 and R2

R1#show clock

10:47:48.508 UTC Fri Aug 9 2002

R2#show clock

10:47:48.508 UTC Fri Aug 9 2002

Example 3-11 confirms that NTP is authenticated (the remote stratum value is 2) by viewing the output of the IOS command show ntp associations detail.

Example 3-11 show ntp associations detail Command on R2