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CCNP ENCOR Certification Cram Notes : Infrastructure

3.1 Layer 2

Layer 2 refers to the Data Link Layer of the OSI model, which is responsible for providing reliable data transfer between adjacent network devices over a physical link. Layer 2 infrastructure includes switches, which are used to forward and filter data frames within a local area network (LAN) based on their MAC addresses.

Topics under Layer 2 infrastructure:

3.1.a Troubleshoot static and dynamic 802.1q trunking protocols

802.1q is a protocol used to tag Ethernet frames with a VLAN ID to enable multiple VLANs to coexist on a single physical switch port.

Troubleshooting 802.1q trunking involves checking the VLAN configuration on the switch ports, verifying that the correct VLANs are allowed on the trunk link, and checking for issues with VLAN mismatches.

Troubleshooting static and dynamic 802.1q trunking protocols involves verifying the configuration of VLANs and trunk links to ensure that traffic is being tagged with the correct VLAN IDs and that VLAN traffic is allowed to pass over the trunk link.

Here are some steps you can follow to troubleshoot static and dynamic 802.1q trunking protocols:

1. Verify that the correct VLANs are configured on the switch ports:

  • Check the VLAN configuration of each switch port connected to the trunk link to ensure that the correct VLANs are allowed on the port.

  • Use the "show vlan" command to check the VLAN configuration.

2. Verify that the correct VLANs are allowed on the trunk link:

  • Check the trunk port configuration to ensure that the correct VLANs are allowed on the trunk link.

  • Use the "show interfaces trunk" command to check the trunk port configuration.

3. Verify that the trunk link is operational:

  • Check the status of the trunk link to ensure that it is operational.

  • Use the "show interfaces" command to check the status of the trunk link.

4. Check for VLAN mismatches:

  • If there are VLAN mismatches between the two ends of the trunk link, traffic may not be tagged with the correct VLAN ID or may be dropped altogether.

  • Use the "show interfaces trunk" command to check for VLAN mismatches.

5. Check for native VLAN mismatches:

  • If the native VLAN of one end of the trunk link does not match the native VLAN of the other end, untagged traffic may not be passed over the trunk link.

  • Use the "show interfaces trunk" command to check for native VLAN mismatches.

By following these troubleshooting steps, you can ensure that 802.1q trunking is configured correctly and that traffic is being passed over the trunk link as expected.

3.1.b Troubleshoot static and dynamic EtherChannels

  • EtherChannel is a technology that allows multiple physical links between switches to be combined into a single logical link, increasing bandwidth and providing redundancy.

  • Troubleshooting EtherChannel involves verifying that the correct ports are configured in the channel group, checking for errors or mismatches in the configuration, and verifying that the channel is operational.

Troubleshooting static and dynamic EtherChannels involves verifying the configuration of the EtherChannel and the physical links that are part of the EtherChannel to ensure that traffic is being balanced across the links and that all links are operational.

Steps you can follow to troubleshoot static and dynamic EtherChannels:

1. Verify that the EtherChannel is configured correctly:

  • Check the configuration of the EtherChannel to ensure that it is configured with the correct mode and protocol.

  • Use the "show etherchannel summary" command to check the configuration of the EtherChannel.

2. Verify that all physical links are operational:

  • Check the status of each physical link that is part of the EtherChannel to ensure that it is operational.

  • Use the "show interfaces" command to check the status of each physical link.

3. Verify that traffic is being balanced across the links:

  • Check the load balancing algorithm that is being used to ensure that traffic is being balanced across the links as expected.

  • Use the "show etherchannel load-balance" command to check the load balancing algorithm.

4. Check for misconfigurations:

  • If there are misconfigurations in the EtherChannel configuration, traffic may not be balanced across the links or may be dropped altogether.

  • Use the "show etherchannel summary" command to check for misconfigurations in the EtherChannel configuration.

5. Verify that the switch is running a compatible version of EtherChannel:

  • If the switch is running an incompatible version of EtherChannel, the EtherChannel may not function properly.

  • Use the "show version" command to check the version of EtherChannel that the switch is running.

By following these troubleshooting steps, you can ensure that EtherChannels are configured correctly and that traffic is being balanced across the links as expected.

3.1.c Configure and verify common Spanning Tree Protocols (RSTP and MST):

Spanning Tree Protocol (STP) is a protocol used to prevent loops in a network by creating a logical tree of connected switches.

Rapid Spanning Tree Protocol (RSTP) is an improvement over STP that provides faster convergence times in response to changes in the network topology.

Multiple Spanning Tree (MST) is a variation of STP that allows for multiple instances of STP to be used on a single switch, each with its own set of VLANs.

Configuring and verifying STP involves setting the root bridge and priority, configuring port roles (root, designated, or blocked), and verifying the forwarding path through the network.

Verifying Spanning Tree Protocols (RSTP and MST)

Verifying Spanning Tree Protocols (STP) involves checking the status of the spanning tree and ensuring that it is functioning correctly to prevent loops in the network.

Here are some steps you can follow to verify common Spanning Tree Protocols, such as RSTP and MST:

1. Verify the STP mode:

  • Check the STP mode that is being used on the switch to ensure that it matches the mode that is being used on the other switches in the network.

  • Use the "show spanning-tree summary" command to check the STP mode.

2. Verify the root bridge:

  • Check the status of the root bridge to ensure that it is operational and that it is the correct root bridge for the network.

  • Use the "show spanning-tree root" command to check the status of the root bridge.

3. Verify the path cost:

  • Check the path cost to ensure that the path that is being used is the shortest path to the root bridge.

  • Use the "show spanning-tree interface [interface]" command to check the path cost.

4. Verify the STP topology:

  • Check the topology of the STP to ensure that there are no loops in the network.

  • Use the "show spanning-tree" command to view the STP topology.

5. Verify the convergence time:

  • Check the convergence time to ensure that the STP is functioning correctly and that convergence occurs within a reasonable amount of time.

  • Use the "show spanning-tree summary" command to view the convergence time.

6. Verify the STP configuration:

  • Check the configuration of the STP to ensure that it is configured correctly and that there are no misconfigurations that could cause issues in the network.

  • Use the "show spanning-tree [vlan]" command to view the STP configuration.

By following these verification steps, you can ensure that Spanning Tree Protocols, such as RSTP and MST, are functioning correctly and that they are preventing loops in the network.


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