“Implementing NTP Clients, Servers, and Client/Server Mode With NTP, servers supply information about the time of day to clients, and clients react by adjusting their clocks to match. The process requires repeated small adjustments over time to maintain that synchronization.… — Wendell Odom Copy Share Image
“Host B can send ICMP echo reply messages to R1’s 172.16.4.1 IP address (hosts send echo reply messages to the IP address from which… — Wendell Odom Copy Share Image
“NTP Using a Loopback Interface for Better Availability An NTP server will accept NTP messages arriving to any of its IPv4 addresses by default.… — Wendell Odom Copy Share Image
“Storing Log Messages for Later Review With logging to the console and to terminals, an event happens, IOS sends the messages to the console and terminal sessions, and then IOS can discard the message. However, clearly, it would be useful to keep a copy of the log messages for later review, so IOS provides two primary means to keep a… — Wendell Odom Copy Share
“Sending Messages in Real Time to Current Users Cisco IOS running on a device at least tries to allow current users to see log messages when they happen. Not every router or switch may have users connected, but if some user is logged in, the router or switch benefits by making the network engineer aware of any issues. By default,… — Wendell Odom Copy Share
“System Message Logging (Syslog) It is amazing just how helpful Cisco devices try to be to their administrators. When major (and even not-so-major) events take place, these Cisco devices attempt to notify administrators with detailed system messages. As you learn in this section, these messages vary from the very mundane to those that are incredibly important. Thankfully, administrators have a… — Wendell Odom Copy Share
“172.16.1.51 and vice versa. You can reasonably assume that the switches learned the MAC addresses of the router and the host, adding those to the MAC address tables. Host A and Router R1 completed the ARP process and list each other in their respective Address Resolution Protocol (ARP) tables. The failure of a ping, even with two devices on the… — Wendell Odom Copy Share
“Configuring and Verifying System Logging With the information in Table 33-2, configuring syslog in a Cisco IOS router or switch should be relatively straightforward. Example 33-2 shows a sample, based on Figure 33-4. The figure shows a syslog server at IP address 172.16.3.9. Both switches and both routers will use the same configuration shown in Example 33-2, although the example… — Wendell Odom Copy Share
“sending of log messages to all logged users. However, that default configuration is not enough to allow the user to see the log messages.… — Wendell Odom Copy Share Image
“First, note that the example configures the same message level at the console and for terminal monitoring (level 7, or debug), and the same level for both buffered and logging to the syslog server (level 4, or warning). The levels may be set using the numeric severity level or the name as shown earlier in Figure 33-3. The show logging… — Wendell Odom Copy Share
“First, to understand why the standard and extended ping results have different effects, consider first the standard ping 172.16.1.51 command on R1, as shown previously in Figure 23-7. As a standard ping command, R1 used its LAN interface IP address (172.16.1.1) as the source of the ICMP Echo. So, when the host (A) sent back its ICMP echo reply, host… — Wendell Odom Copy Share
“root cause of the problem may be happening, further isolating the problem. This section begins with a brief explanation of how ping works. It… — Wendell Odom Copy Share Image
“For instance, consider the topology in Figure 33-6, with Router R4 on the right acting as NTP server and the other routers acting as clients. R4 has three IP addresses that the clients could put in their ntp server address commands. Now consider what happens when one interface on R4 fails, but only one. No matter which of the three… — Wendell Odom Copy Share
