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How To Configure HSRP

February 2, 2015 by Rowell Dionicio 1 Comment

Below are my notes for the CCNP Routing & Switching SWITCH 300-115 certification exam. I used two Cisco 3560 switches and GNS3 to perform my labs. For theory, I used Cisco Configuration Guides and the Cisco Press Official Certification Guide.

Hot Standby Router Protocol, HSRP, is a Cisco proprietary protocol to make multiple routers or switches appear as one gateway. The gateway is where the redundancy is provided. For each redundant gateway, there is a common HSRP group. One router/switch becomes the primary HSRP router and another is selected as the standby HSRP router. Any other devices part of the group are in the listen HSRP state.

HSRP Configuration
R1 and R2 will be HSRP enabled.

At a 3 second interval, routers send HSRP hello messages to become aware if the other is up or down (between Active and Standby). The hold time value is 10 seconds or three times the hello timer. These hello messages are sent to the multicast address 224.0.0.2 using UDP port 1985.

There can be up to 255 HSRP groups and they are only locally significant.

Election of an active and standby HSRP router is based on a priority value of 0 through 255. By default, the priority is 100 but the highest priority value becomes the active router for the HSRP group. If there is a tie, the router with the highest IP address becomes the active router.

When HSRP is enabled, an interface goes through the following states:

  • Disabled
  • Init
  • Listen
  • Speak
  • Standby
  • Active

Configuration

I will use R1 and R2 as the two routers to provide a redundant gateway for 192.168.1.1. [Read more…] about How To Configure HSRP

What Is EtherChannel Misconfiguration Guard

September 25, 2014 by Rowell Dionicio Leave a Comment

EtherChannel Guard is a way of finding out if one end of the EtherChannel is not configured properly. This could be that there are some parameters not matching up such as duplex and speed. Or it could be that one side is a trunk and the other isn’t.

When there is a misconfiguration found, the switch will place the interfaces in error-disabled state and an error will be displayed.

Configuration

To enable EtherChannel Guard, issue the global command:

SW1(config)#spanning-tree etherchannel guard misconfig

Verification

SW1#show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID is enabled
Portfast Default is disabled
PortFast BPDU Guard Default is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default is disabled
EtherChannel misconfig guard is enabled
UplinkFast is disabled
BackboneFast is disabled
Configured Pathcost method used is short

Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
Total 0 0 0 0 0

To view any disabled interfaces issue the show command:

show interfaces status err-disabled

VTP Message Types

December 24, 2013 by Rowell Dionicio Leave a Comment

VTP communication between switches is done through three different advertisements:

  • Summary Advertisements
  • Subset Advertisements
  • Advertisement Requests

Summary Advertisements

In 5 minute intervals, a VTP server will send a Summary Advertisement to it’s adjacent switches. Included in this VTP Summary Advertisement is the VTP domain name and configuration revision number.

Another VTP Server or Client receives the Summary Advertisement and compares the VTP domain name and revision number to its own. If the domain name is different, it ignores the advertisement. If its own configuration revision number is higher than the request, it ignores the advertisement. If the configuration revision number is higher than its own, it sends an advertisement request. Following Summary Advertisements are Subset Advertisements.

Subset Advertisements

Changes made to VLANs will increment the configuration revision number and issue a Summary Advertisement followed by one or more subset advertisements. The Subset Advertisement is what holds the VLAN information.

Advertisement Requests

When a switch needs VTP information it sends an Advertisement Request. This request is sent if the switch has been reset, VTP domain name has changed, or it received a VTP Summary Advertisement with a higher configuration revision. Following the Summary Advertisement are Subset Advertisements.

What Is A Cisco Routed Port

December 18, 2013 by Rowell Dionicio Leave a Comment

[Study CCNA or CCNP SWITCH with Cisco Press]

A routed port on a switch can act like a port on a router. Routed switch ports aren’t joined to any VLANs and they do not support VLAN subinterfaces. Because they are routed ports, you can configure a Layer 3 protocol. And because the routed port is acting as a Layer 3 interface it will not support Layer 2 protocols.

Configuring Routed Ports

Get into interface configuration mode of a switch and issue the command no switchport. This disables Layer 2 capabilities and enables Layer 3. You can then assign an IP address to the interface.

Although limited, you can enable a routing protocol to assign routing capabilities to the port.

[Read more…] about What Is A Cisco Routed Port

Configuring Cisco VTP

December 2, 2013 by Rowell Dionicio Leave a Comment

VLAN Trunk Protocol (VTP) is a Cisco-proprietary protocol used to replicate VLANs using Layer 2 trunk frames to other switches. It is a method to ease administration by selecting a switch to be configured as a VTP server.

VLANs are configured on the VTP server and then replicated to other connected switches, called VTP clients. This reduces the amount of configuration — having to log onto each switch to create a VLAN. All VLAN and VTP data is saved in the vlan.dat file – stored in the switch’s flash memory.

[Study CCNA or CCNP SWITCH with Cisco Press]

VTP Domain

VTP is organized into management domains, which share common VLAN requirements. These management domains are called VTP Domains. A switch can only be joined to one VTP domain. Each VTP domain is isolated from one another. Information is not shared between VTP domains.

VTP Modes

Switches can be configured in one of three VTP modes:

Server Mode – switch has full control over creating and modifying VLANs. This is the default mode for a switch.

Client Mode – switch cannot create, modify, or delete any VLANs. Switches listen to VTP Advertisements.

Transparent Mode – switch doesn’t participate in VTP. A switch in Transparent Mode will forward VTP version 2 VTP Advertisements out it’s trunk ports — acting as a relay — if it receives VTP Advertisements.

[Read more…] about Configuring Cisco VTP

Configuring Trunks on Cisco Switches

November 25, 2013 by Rowell Dionicio 2 Comments

A trunk will allow multiple VLANs to transport between switches. Trunk ports can be configured in two ways, the Cisco proprietary Inter-Switch Link, ISL, or with the standard IEEE 802.1Q

Personally, I don’t use ISL and you shouldn’t either. But lets understand its differences with 802.1Q.

Inter-Switch Link (ISL)

ISL is Cisco proprietary in how it adds the VLAN tag to a frame. It will encapsulate a whole frame, adding a 26-byte header and a 4-byte trailer. The VLAN number is placed in the header.

ISL Header
ISL Header

[Read more…] about Configuring Trunks on Cisco Switches

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