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How To Configure HSRP

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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

Book Review: CCNP SWITCH 300-115 Official Cert Guide

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Book Review: CCNP SWITCH 300-115There are only a handful of books to select from when studying for the CCNP SWITCH 300-115 exam. It’s tough to make the right decision on a resource for an exam that costs $250 to sit in. My go-to book resource is Cisco Press. In short, I passed the CCNP SWITCH (300-115) exam on January 20th, 2015 with the assistance of CCNP SWITCH 300-115 Official Cert Guide.

When I started studying for this exam on October 31st, 2014, there wasn’t a book available covering the new objectives. I printed the exam objectives and started reading configuration guides. As soon as the books were available, I put an order in with Cisco Press and I was off.

The author, David Hucaby, did a great job with his explanations. The book itself isn’t as big as ROUTE. What I like about this book is it is easy to follow along with Cisco’s objectives. After passing the exam, I can say that it covers it very well. David helped me to understand topics where I was weak. It helped reinforce the fundamentals of Spanning Tree and redundancy such as GLBP.

Within the book are good diagrams and configuration examples. The little details are in there as well such as timers, intervals, etc. You’ll need to remember those for the exam.

In preparation for the exam, each chapter is preluded with a chapter quiz. I used those pre-chapter quizzes after I have read through the entire book. The questions are very good compared to the exam. I dig deeper into other topics where I score lower than 80%. Each chapter has anywhere from 10-15 questions so it’s not something to rely on. [Read more…] about Book Review: CCNP SWITCH 300-115 Official Cert Guide

Configuring PAgP EtherChannel

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There are three different methods to create an EtherChannel. One of them is Cisco’s own proprietary protocol, PAgP, Port Aggregation Protocol. It is similar to LACP which is the industry standard. A PAgP link is usually used between Cisco switches.

PAgP will aggregate physical port links into one logical link to provide redundancy and increased bandwidth. Within a PAgP link there can be up to eight active ports. PDUs are sent on the lowest numbered VLAN on the trunk link. Each port joining the PAgP link must have the same configuration.

There are two modes used in PAgP:

  • Auto
  • Desirable

Auto mode will passively negotiate PAgP. If the remote end of the link is also configured with Auto mode, a PAgP EtherChannel will not form.

Desirable mode will actively negotiate PAgP. The remote end must be configured in Auto or Desirable mode for a PAgP EtherChannel to form.

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Configuration

To configure PAgP, identify the physical ports which will join to the same logical bundle.

SW1#config t
 SW1(config)#interface range f0/1 - 2
 SW1(config-if)#channel-group 5 mode desirable
 SW1(config-if)#end
SW2#config t
 SW2(config)#interface range f0/1 - 2
 SW2(config-if)#channel-group 5 mode desirable
 SW2(config-if)#end

Let’s break down the command that creates the PAgP bundle.

channel-group 5 is how we identify that we want to create an EtherChannel. 5 is the identifying value we want to assign to this EtherChannel. Depending on your switch/IOS version you will have a specific range of numbers available to use.

To find out which EtherChannel numbers already in use issue the command show etherchannel summary.

mode desirable is how we configure these interfaces to actively negotiate PAgP. If we wanted the interfaces to passively negotiate a PAgP link then we would configure it with mode auto.

The remote end of the link is configured similarly with the difference being that the channel-group numbers do not have to match.

After configuring the interfaces to be part of the same channel-group, a port-channel will automatically be configured. This is the logical interface of the bundle. The port-channel number will be the same as your channel-group number. In the example above, port-channel 5 was automatically created.

You can view this port-channel interface with the following commands:

  • show interface status
  • show interfaces po5

[Read more…] about Configuring PAgP EtherChannel

What Is EtherChannel Misconfiguration Guard

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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

Configuring EtherChannel Layer 2 and Layer 3

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In previous notes about EtherChannel, we went over configuration of LACP and PAgP. Now we move on to configuring Layer 2 and Layer 3 EtherChannels. The difference is clear.

Layer 2 EtherChannels are assigned to only one VLAN and it is an access mode.

Layer 3 EtherChannels are placed in Layer 3 mode with the no switchport command. The logical interface has an IP address assigned to it.

Layer 2 EtherChannel Configuration

In this process, a port-channel interface is created.

SW1#conf t
SW1(config)#interface f0/1
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 10
SW1(config-if)#channel-group 10 mode active
SW1(config-if)#end
SW2#conf t
SW2(config)#interface f0/1
SW2(config-if)#switchport mode access
SW2(config-if)#switchport access vlan 10
SW2(config-if)#channel-group 10 mode active
SW2(config-if)#end
SW1#show etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
10 Po10(SU) LACP Fa0/1(P)

The Port-channel column shows flags SU which means it is Layer 2 and it is in use. Mission accomplished. [Read more…] about Configuring EtherChannel Layer 2 and Layer 3

Configuring LACP, PAgP, and Manual

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Bundling multiple ports into one logical interface is a common configuration. It is otherwise known as bundling, port channel or EtherChannel. You can combine multiple interfaces into one of these three modes:

  • LACP
  • PAgP
  • On

LACP

Link Aggregation Control Protocol is the standard 802.3ad. You combine multiple links into a single logical link to increase bandwidth and redundancy. All links participating in a single logical link must have the same settings such as duplex mode, link speed, and interface mode such as access or trunk. You can have up to 16 ports in an LACP EtherChannel but only eight can be active at one time.

LACP can be configured in either passive or active mode. In active mode, the port actively tries to bring up LACP. In passive mode, it does not initiate the negotiation of LACP.

There are a few parameters which can be configured with LACP ports:

  • System Priority – Forms the system ID and is used during negotiation.
  • Port Priority – Used to decide which ports should be put in standby mode when there is a limitation or something preventing a port from aggregating.
  • Administrative Key – Defines the ability of a port to aggregate with other ports.

In the event one of the links within an LACP bundle fails, traffic continues to flow on the other available links in the bundle. [Read more…] about Configuring LACP, PAgP, and Manual