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Architecture CCNP Enterprise Core (350-401) Cisco

Cisco DNA Centre Assurance

Cisco DNA Centre Assurance provides a tool for handling relevant customer requirements with the following capabilities:

  • Cisco SD-Access Fabric Configuration
  • Software Image Management (SWIM)
  • Simplified Provisioning for Devices
  • Wireless Network Management
  • Simplified Security Policies
  • Configuration Templates
  • Network Assurance
  • Plug and Play

Cisco DNA Centre Assurance provides a feature called Network Time Travel in Network Assurance. It allows the network administrator to play back an event that happened in the network at a particular date and time to try locate the source of an issue; for example a user was unable to connect to the wireless network at 3pm.

Network Assurance can show what is happening in the network now plus show what is happening in the network with predicted trends for the future.

If an issue is found, Network Assurance can use artificial intelligence to try provide guided remediation steps to fix the problem.

Network Assurance provides an overall view of the health of the network from wired to wireless clients, to switches and other network devices.

A simple search in Network Assurance can provide all the information needed for a network administrator to troubleshoot an issue, in comparison to multiple show commands being required to be ran on multiple network devices.

The information presented can be as much as:

  • The device type
  • The OS version
  • The MAC address
  • The IPv4 address
  • The VLAN ID
  • Connectivity Status
  • When the device was last seen
  • What network device the device is connected too
  • Wireless SSID used
  • Last known location

Network Assurance can provide this information due to the APIs it can use to integrate with technologies such as Active Directory, Identity Services Engine (ISE), ServiceNow and Infoblox.

Network Assurance includes a tool called Path Trace. Path Trace is a visual traceroute tool that can be ran periodically or continuously.

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

IP SLA

IP SLA is a tool built into Cisco routers. It allows for the continuous monitoring on parts of the network.

There are number of different types of probes that can be set up with IP SLA to monitor different things, such as:

  • Delay
  • Jitter
  • Packet Loss
  • Packet Sequencing
  • Path
  • Connectivity
  • Server or Website Download Time
  • Voice Quality

Configuring an IP SLA

ip sla 10
 icmp-echo 192.168.1.50 source-interface GigabitEthernet0/0
  frequency 300

The above example will send an ICMP echo to 192.168.1.50 sourced from the IP address on GigabitEthernet0/0 every 300 seconds

The SLA can be switched on with the following command

ip sla schedule 10 life forever start-time now

There is many options on when an SLA should start, and how long it should last for. The above configuration starts the SLA monitoring immediately with no expiration.

The SLA configuration can be viewed with the command show ip sla configuration 10

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Encapsulated Remote SPAN (ERSPAN)

Like RSPAN, ERSPAN has the ability to take source SPAN traffic from one remote switch and deliver it to a host that can analyse traffic.

ERSPAN differs from RSPAN in that ERSPAN uses Layer 3, RSPAN uses Layer 2.

The start of a ERSPAN is configured with the command:

monitor session 10 type erspan-source

This defines the session number and the fact it is a ERSPAN.

With the initial command inputted, it will enter into a sub-menu where the rest of the session can be configured

 description TSHOOT
 source interface GigabitEthernet1/1
 no shutdown
 destination
  ip address 192.168.1.50
  erspan-id 2
  origin ip address 192.168.10.1
 exit
 erspan ttl 30

To verify the ERSPAN command on the switch, type show monitor session erspan-source session

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Remote SPAN (RSPAN)

In a larger environment, there may be a need to forward mirrored traffic across multiple switches to reach the traffic analyser.

From the source port, the mirrored traffic placed on a special VLAN called a RSPAN VLAN. The RSPAN VLAN acts differently from a regular VLAN.

Any ports that are associated with the RSPAN VLAN to not learn any MAC addresses. This ensures that the port associated with the VLAN does not try to use the port associated with the RSPAN VLAN to transmit data to a host.

Traffic is flooded out of all ports associated with a RSPAN VLAN. This means that the RSPAN VLAN should not be associated with ports that are not trunk ports between the source port and destination port.

To configure the RSPAN VLAN, on each switch that will partake in forwarding the SPAN traffic, configure the VLAN:

vlan 500
 name RSPAN
 remote-span

Next, configure the SPAN on the source switch:

monitor session 10 source interface GigabitEthernet0/1
monitor session 10 destination remote vlan 500

On the destination switch, complete the configuration to mirror the traffic from the VLAN to the destination port

monitor session 10 source remote vlan 500
monitor session 10 destination interface GigabitEthernet0/0

The RSPAN session can be verified with the command show monitor session

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Local SPAN

The most basic form of packet capture, the destination of mirrored traffic configured by SPAN is another port on the local switch.

The source of the packet capture can be one of the following interfaces:

  • One or more specific switch ports
  • An entire port channel
  • All of the ports assigned to a VLAN

There are some considerations when setting up a local SPAN session

  • Most switches can support more than two SPAN sessions
  • The source port can not be re-used for more than one SPAN session
  • Source ports can be switch or routed ports
  • The destination can not be reused between multiple SPAN sessions
  • It is possible to saturate the destination port, for example a port channel being mirrored to a single destination port, or a 10Gbps port being mirrored to a 1Gbps port

Specifying a Source Port

The source port can be defined with the global configuration command monitor session <session-id> source.

Complete the command by choosing to mirror a interface or vlan. Finally complete the configuration line on whether to mirror received traffic with rx, transmitted traffic with tx, or both

monitor session 10 source interface GigabitEthernet0/0

If the port is a trunk port and you wish to only pick out a single VLAN, the following command can assist with that:

monitor session 10 filter vlan <vlan-id>

Specifying a Destination Port

The destination port is defined with the global configuration command

monitor session <session-id> destination interface <interface-id>

There a number of additional options that can be applied with setting the destination port.

The SPAN session with it’s default configuration copies traffic without any 802.1Q tags or Layer2 Protocols. Adding encapsulation replicate on as an option will include this additional data.

By default the port used for the destination only egresses mirror traffic but drops ingress traffic. Adding a dot1q vlan keyword on the end will expect any received traffic to be encapsulated with the VLAN ID specified. Adding untagged vlan will encapsulate any received traffic in the chosen VLAN.

Verifying the configuration

The configuration can be verified with the command show monitor session followed by the session ID

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Switched Port Analyser (SPAN)

Switched Port Analyser technologies give a network administrator the ability to see a copy of the traffic that is transmitted on the wire.

The network device when configured with a SPAN technology will mirror all traffic at a data plane level for a specific criteria (port) to a destination. The destination could be a port on the local switch or a remote port connected to a traffic analyser.

Cisco switches provide three types of switched port analysers to make it possible to capture traffic:

  1. Local Switched Port Analyser (SPAN): Capture local network traffic on the switch and send a copy of the network traffic to another port on the switch
  2. Remote Switched Port Analyser (RSPAN): Capture local network traffic on the switch and send a copy of the network traffic through Layer 2 to a remote switch that is connected to a traffic analyser.
  3. Encapsulated Remote Switched Port Analyser (ERSPAN): Capture local network traffic on the switch and send the traffic to a system through Layer 3 routing to a remote device connected to a traffic analyser.

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Network Diagnostics: Netflow

It is possible to gather flows of network traffic as they traverse through devices.

This can be useful for many reasons, for billing or for checking if traffic is flowing optimally through the network.

This is done with Netflow, and requires two parts to be configured for it work, Netflow Data Capture and Netflow Data Export.

The Netflow Data Capture captures the traffic statistics on the network device.

The Netflow Data Export exports this data to a NetFlow collector, such as DNA Center or Cisco Prime Infrastructure.

Before enabling Network on a network device, it is important to note that it is does consume memory on the platform. Ensure the network device has enough memory to support Netflow and usual network operations.

Netflow can capture traffic on both the egress and ingress of a port.

Traffic that can be collected on egress/ingress on Netflow Version 9

Ingress TrafficEgress Traffic
IP to IP PacketsNetflow accounting for all IP traffic packets
IP to Multiprotocol Label Switching (MPLS) packetsMPLS to IP Packets
Frame Relay Terminated Packets
ATM Terminated Packets

Netflow collects information based on flows.

A flow is a unidirectional traffic stream that can contain a combination of the below data:

  • Source IP address
  • Destination IP address
  • Source port number
  • Destination port number
  • Layer 3 Protocol Type
  • Type of Service (ToS)
  • Input Logical Interface

Configuring NetFlow

config terminal
ip flow-export version 9
ip flow-export destination 192.168.1.50 9997

interface GigabitEthernet1/1
ip flow ingress
ip flow egress

Network can be verified that it is working correctly with the commands show ip flow interface, show ip flow export, show ip cache flow

Top Talkers

Enabling NetFlow brings an advantage to network administrators that they can quickly view the top connections on the network device with a simple command, show ip flow top-talkers

It requires a little bit more configuration to enable it on the router in global configuration mode

ip flow-top-talkers
 sort-by bytes
 top 15

Flexible NetFlow

Flexible NetFlow was developed to provide an option for further network traffic analysis than is possible with normal NetFlow.

Flexible Netflow allows for the use and re-use of configuration components.

Flexible NetFlow allows the use of multiple Flow Monitors at the same time, meaning multiple flow policies can be applied to the same traffic as it flows through the device.

If there two different destinations to put NetFlow traffic, the same traffic can be analysed in two different ways then sent onto two different destinations.

Flexible NetFlow is broken down into four separate components

Flow Records

Flow records are a combination of key and non-key fields. Predefined and user records.

Flow Monitors

Flow monitors are applied to the interface to monitor network traffic

Flow Exporters

Flow exporters export NetFlow version 9 data from the Flow Monitor cache to a remote host

Flow Samplers

A flow sampler samples partial relevant NetFlow data rather than analysing all NetFlow data.

With the use of sampled NetFlow data, it reduces the load on memory and CPU on the network devices. There is a trade off that data collected may not give as accurate conclusions in comparison to all NetFlow data being collected.

Security is driver of the adoption of Flexible NetFlow due to the ability to track all parts of the IP header as well as the packet, normalising it into a single flow.

Flexible NetFlow can create a dynamic cache of each type of flow and filter ingress traffic to a specific destination.

Flow Records

Creating a customised Flow Record can be done with collect and match commands to match a flow record.

The match command is used to select a key field, the collect command is used to select a non-key field.

FieldKey/Non-KeyDefinition
IP ToSKeyValue in type of service field
IP ProtocolKeyValue in IP Protocol Field
IP Source AddressKeySource IP Address
IP Destination AddressKeyDestination IP Address
Transport Source PortKeySource Port
Transport Destination PortKeyDestination Port
Interface InputKeyInterface Received
Flow Sampler IDKeyID number of Flow Sampler
IP Source ASNon-KeySource AS number
IP Destination ASNon-KeyDestination AS number
IP Next-Hop AddressNon-KeyNext-hop address
IP Source MaskNon-KeySubnet source mask
IP Destination MaskNon-KeySubnet destination mask
TCP FlagsNon-KeyValue in TCP flag field
Interface OutputNon-KeyOutbound interface
Counter BytesNon-KeyNumber of bytes in flow
Counter PacketsNon-KeyNumber of packets in flow
Time Stamp System Uptime FirstNon-KeySystem uptime when packet was first switched
Time Stamp System Uptime LastNon-KeySystem uptime when packet was last switched
Flow Record Fields

Configuring a flow record is important with Flexible NetFlow as the flow record defines what type of traffic will be monitored and analysed.

Custom flow records can have many different combinations to meet the needs of the configuration required.

To define a flow record:

  1. Define the flow record name
  2. Set a description for the flow record
  3. Set match criteria for key fields
  4. Set non-key field data to be collected
flow record MyFlowRecord
 description Capture Flow Record for IPv4
 match ipv4 destination address
 collect counter bytes
 collect counter packets

Flow Exporter

With a custom Flow Record, they need to be exported with a Flow Exporter.

To create a Flow Exporter

  1. Define the flow exporter name
  2. Set a description for the flow exporter
  3. Specify a destination for the flow exporter
  4. Specify the NetFlow version to be used for export
  5. Specify the UDP port to be used for export
flow exporter MyFlowExport
 description My flow exporter
 destination 192.168.1.50
 export-protocol netflow-v9
 transport UDP 9997

Flow Monitor

With the Flow Record and Flow Exporter programmed, it needs to be tied together with the Flow Monitor.

The Flow monitor has it’s own cache. The Flow Record earlier describes how that cache is to be used for capturing NetFlow data.

The steps on configuring a Flow Monitor:

  1. Define the flow monitor name
  2. Set a description for the flow monitor
  3. Specify the flow record to be used
  4. Specify a cache timeout
  5. Assign the exporter to a monitor
flow monitor MyFlowMonitor
 description Flow Monitor
 record MyFlowRecord
 cache timeout active 60
 exporter MyFlowExport

Turn on Flexible NetFlow

The flow monitor needs to be applied to the appropriate interface where traffic will be captured

interface GigabitEthernet0/1
 ip flow monitor MyFlowMonitor input

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Network Diagnostics: syslog

Devices can generate large amounts of information.

The information can be sent to the device logging buffer, onto the console screen, or to a syslog server. Different logging levels can be set for all three.

Level DefinitionLevelDescriptionsyslog Definition
emergencies0System UnstableLOG_EMERG
alerts1Immediate Action NeededLOG_ALERT
critical2Critical ConditionLOG_CRIT
errors3Error ConditionLOG_ERR
warnings4Warning ConditionLOG_WARNING
notifications5Normal but significant conditionLOG_NOTICE
informational6Informational MessageLOG_INFO
debugging7Debugging MessageLOG_DEBUG
Levels of logging

Logging to Memory Buffer

Logging can be enabled to the buffer with the command logging buffer followed by the logging level chosen numerically (0-7) or by definition (debugging, errors, alerts)

The default size of the logging buffer is only 4096 bytes, so it is a good idea to extend it with the command logging buffer followed by the size in bytes.

Logging to Syslog Server

Logging to a syslog server can be carried out with the command logging host followed by the IP address of the host

To modify the logging level used with syslog, use the command logging trap followed by the logging level of detail required numerically

Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Network Diagnostics: Simple Network Management Protocol

Simple Network Management Protocol (SNMP) provides a way for network engineers to get reactive alerts when something changes in the network.

SNMP can be used to configure devices too, but this is less common.

SNMP can send traps to a SNMP collector or network management system in response to a change that has happened in the network.

These traps or events are defined as part of a management information base (MIB). The MIB is a database of parameters that are triggered by these network events.

There are three versions of SNMP, SNMPv1, SNMPv2c, and SNMPv3

SNMPv1 uses a community string for authentication, and offers no encryption on data sent or received.

SNMPv2c again uses a community string for authentication with no encryption. It offers much better error handling and error code information over SNMPv1.

SNMPv3 is a major change to versions 1 and 2c. It can offer authentication based on HMAC-MD5 or HMAC-SHA algorithms in it’s authNoPriv mode.

SNMPv3 can go a step further in authPriv mode and offer encryption with Data Encryption Standard (DES) or Advanced Encryption Standard (AES)

As a result, SNMPv3 offers the most privacy and security options over the other two versions.

Offering username and password authentication over simple community strings is a major step for security in comparison to other versions.

SNMPv1 and SNMPv2c can use access lists to help secure access to their platforms by only whitelisted IP addresses.

Community strings can be set to read-only or read-write; so it can restrict SNMP agents to a ‘observation-only’ mode if set to read-only.

If no version is specified on a network device, SNMPv1 is used by default.

SNMP Operations

For communications between a network management system and a network device, SNMP use a number of operations

get-request

Retrieve a value from a specific variable.

get-next-request

Retrieve a value from a variable within a table

get-bulk-request

Retrieve a large block of data, such as multiple rows in a table with one transaction rather than multiple

get-response

Replies to a get-request, get next request

set-request

Stores a value in a specific variable

trap

Sends an unsocialised message from an SNMP agent to a SNMP manager when an event has occurred

Defining a SNMP community

To define a secured SNMP community for SNMP v1 or v2c for the network 192.168.1.0

access-list 10 permit 192.168.1.0 0.0.0.255
snmp-server community SNMPCOMM ro 10

The above will create a read only community with the SNMP community string SNMPCOMM. Any network management server in the subnet 192.168.1.0 – 192.168.1.255 can poll the network device with the community string SNMPCOMM

Sending traps

A network device can be configured to send traps to a network management server.

snmp-server enable traps
snmp-server host 192.168.1.50 traps SNMPCOMM

The router can be configured to send only specific categories of traps by affixing parameters on the first command

snmp-server enable traps config
Categories
Architecture CCNP Enterprise Core (350-401) Cisco

Network Diagnostics: Debugging

Debugging can provide important information to a network engineer when troubleshooting an issue. One of the important reasons for enabling debugging is to check at a deeper level why something is not working as it should be.

Debugging can sometimes be too informational, so access lists can be used on some debug commands to restrict the output, for example with debug ip packet <access-list>. Some debugging features allow it to be restricted to an interface rather than all interfaces on a network device.