CCIE Routing & Switching v4.0 Quick Reference: Network Optimization
This chapter is from the book
This chapter is from the book
This chapter is from the book
IP Service Level Agreement (SLA)
One of the most important aspects in maintaining a network is providing a guarantee of a specific level of service to customers. To ensure that such an agreement is met at all times, IOS provides a mechanism to actively test specific metrics, called IP SLA. When configured, the IP SLA service actively monitors a specific aspect of the network, such as UDP VOIP jitter, DNS response time, ping latency, and so on. If the IP SLA thresholds are not met, IOS sends a notification, such as an SNMP trap or syslog message.
To create a basic IP SLA monitor, the type, options, and frequency must be specified. After the monitor has been created, a schedule is build that kicks off the monitor. To monitor the round-trip response time between a router and an IP, you can use the ICMP Echo Operation:
Router(config)# ip sla monitor <OPERATION #>
Router(config-sla-monitor)# type echo protocol ipIcmpEcho <DESTINATION>
Router(config-sla-monitor)# frequency <SECONDS>
Router(config-sla-monitor)# exit
Router(config)# ip sla monitor schedule <OPERATION #> [life {forever | seconds}] [start-time {hh:mm[:ss] [month day | day month] | pending | now | after hh:mm:ss] [ageout seconds] [recurring]
Some monitors require that a responder be configured (UDP Jitter, UDP Echo, and TCP Connect) on one router:
Router(config)# ip sla monitor responder
Following are other IP SLA monitor operations:
UDP Jitter: type jitter VOIP Jitter: type VOIP Gatekeeper Delay: type voip delay gatekeeper registration UDP Echo: type udp echo HTTP Connect: type http operation TCP Connect: type tcpConnect ICMP Echo: type echo protocol ipIcmpEcho ICMP Path Echo: type pathEcho protocol ipIcmpEcho ICMP Path Jitter: type pathJitter FTP Operations: type ftp DNS Operations: type dns DHCP Operations: type dhcp
NetFlow
As packets are sent through router interfaces, they can be classified into flows. This information can be sent from the router to a monitoring server that can provide valuable information about the traffic traversing the network. A flow can be described by a number of fields:
- Source IP address
- Destination IP address
- Source port
- Destination port
- Protocol type
- Type of Service
- Interface
To determine if a packet belongs in a particular flow, the seven packet fields are inspected. If any one of the fields is different, the packet in question can be considered a new flow. NetFlow statistics can be collected on the following types of networks: IP, Frame Relay, MPLS, and ATM.
To enable NetFlow on an interface, the ip flow command set is used. To configure NetFlow on an interface:
Router(config-if)# ip flow ingress Egress support can also be added: Router(config-if)# ip flow egress
To configure the router to export the NetFlow data to a NetFlow server
Router(config)# ip flow-export {destination {ip-address | hostname} udp-port | source {interface-name} | version {1 | [{5 | 9} [origin-as | peer-as] [bgp-nexthop]]} | template {refresh-rate packets | timeout-rate minutes} [options {export-stats | refresh-rate packets | sampler | timeout-rate minutes}]}
To be exported to the NetFlow collection server, the flow must have been exported from the flow cache. Active flows (when there is an ongoing conversation) live for 30 minutes by default before they are exported. Inactive flows, those that have been terminated, are sent after 15 seconds. These values are configurable:
Router(config)# ip flow-cache timeout [active minutes | inactive seconds]
The number of flows that can be collected can be modified with:
Router(config)# ip flow-cache entries <#>
SPAN, RSPAN, and Router IP Traffic Export (RITE)
Viewing the packets between two devices is often the best way to troubleshoot a networking issue. Many organizations deploy network monitoring servers for both network functionality and security purposes. To provide these servers a stream of data from all segments of the network, the Switched Port Analyzer (SPAN) mechanism built into Cisco switches can be used. A SPAN port is a physical port that is configured to send data received on other ports or VLANs. When the data is sent out the SPAN port, it is simply a copy of all the data that has been sent through the configured source ports.
To configure the source of the data to be sent out the SPAN port
Router(config)# monitor source <#> source {interface interface-id | vlan vlan-id} [, | -] [both | rx | tx]
Either a source interface or entire VLAN can be specified. You can use the command multiple times with the same session number if multiple sources are used.
To configure the destination of the data to be sent:
Router(config)# monitor destination <#> destination interface <INT>
The data received in the source interface is sent to the specified destination interface.
The SPAN functionality assumes that the destination of the traffic is directly connected to the switch. If the network is large, it might not be possible to wire a single monitoring station to multiple switches with SPAN ports. Fortunately a special remote SPAN (RSPAN) VLAN can be created that transports the SPAN port information to another switch. This enables an aggregation of monitoring data into a single VLAN that can be sent to the monitoring station.
To configure the RSPAN VLAN, the remote-span command must be specified within the VLAN configuration mode:
Router(config-vlan)# remote-span Specify the destination of the SPAN port as the remote-span VLAN: Router(config)# monitor session <#> destination remote vlan <VLAN>
This is great for switches, but is there a similar technology for a router? Yes! The Router IP Traffic Export (RITE) mechanism can export traffic to specific devices defined by the MAC address. To configure, a RITE profile is created and then it’s applied to an interface. The traffic that RITE applies to can be limited by ACLs.
To configure the profile
Router(config)# ip traffic-export profile <PROFILE NAME> Specify the outgoing interface: Router(config-rite)# interface <INT> Specify the MAC address to send the traffic to: Router(config-rite)# mac-address <MAC>
Specify whether bidirectional traffic is necessary. Without this command, only packets incoming to the router are sent:
Router(config-rite)# bidirectional
Optionally, ACLs can limit the traffic sent:
Router(config)# incoming {access-list {standard | extended | named} | sample one-in-every packet-number}
Router(config)# outgoing {access-list {standard | extended | named}| sample one-in-every packet-number}
Apply the RITE policy to an interface:
Router(config-if)# ip traffic-export apply <POLICY NAME>
Cisco IOS Embedded Event Manager (EEM)
In the normal operations of the switch or router, events such as a CLI command, a syslog message, or an SNMP trap, for example, are constantly occurring. These events are detected by the EEM Event Detectors that send their information to the EEM server. The EEM server can then be programmed to implement an EEM policy. The two different types of EEM policies are applets and TCL scripts, which can be programmed to perform a variety of tasks, such as send syslog messages and SNMP traps, fire off emails, and even open raw sockets.
An applet can be configured directly within the IOS CLI by first creating a policy and registering it:
Router(config)# event manager applet <APPLET NAME>
The applet must be configured to detect a specific event. There are a number of different event detectors, each with their own syntax:
Router(config-applet)# event <EVENT DETECTOR>
-
application: Application-specific event
-
cli: CLI event
-
counter: Counter event
-
interface: Interface event
-
ioswdsysmon: IOS WDSysMon event
-
none: Manually run policy event
-
oir: OIR event
-
snmp: SNMP event
-
syslog: Syslog event
-
timer: Timer event
The actions of the applet that are performed when the programmed event occurs are entered line by line:
Router(config-applet)# action <LABEL> <ACTION>
Some of the actions are predefined within IOS:
- Executing a Cisco IOS command-line interface (CLI) command (cli)
- Setting or modifying a named counter (counter)
- Switching to a secondary processor in a fully redundant hardware configuration (force-switchover)
- Requesting system information when an event occurs (info)
- Sending a short e-mail (mail)
- Manually running an EEM policy (policy)
- Publishing an application-specific event (publish-event)
- Reloading the Cisco IOS software (reload)
- Generating an SNMP trap (snmp-trap)
- Generating prioritized syslog messages (syslog)
Unfortunately, a TCL script cannot be created on the CLI, it must be uploaded to the router. When uploaded, it must be registered:
Router(config)# event manager policy <FILENAME>