What families of Catalyst switches provide for the option for redundant Supervior Engines?

Catalyst 4500 and 6500 families

Describe the general purpose of Route Processor Redundancy.

The Catalyst 4500 and 6500 families of switches support high availability by allowing a redundant Supervisor Engine to take over if the primary Supervisor Engine fails for both L2 and L3 functions.

Which events can trigger a switchover from the active to the standby Supervisor Engine?

- RP and SP crash on the active Supervisor Engine

- A manual switchover from the CLI

- Removal of the active Supervisor Engine

- Clock synchonization failure between Supervirsor Engines. 

What happens to the other modules when an RPR failover occurs?

- All switching modules are power cycled

 

- Remaining subsystems on the MSFC (including L2 and L3 protocols) are initialized on the prior standby, now active Supervisor Engine. 

 

- ACLs based on the new active Supervisor Engine are reprogrammed into the Supervisor Engine hardware. 

How does the redundant Supervisor Engine work with Route Processor Redundancy Plus?

What must be the same on both Supervisor Engines for RPR+ to run?

The active Supervisor Engine checks the image version of the standby when the standby Supervisor Engine comes online. If the image on the standby does not match the image on the active, RPR redundancy mode is used.

What are some of the benefits of using RPR+ over RPR?

- Reduced switchover time

 

- No reloading of installed modules

 

-  Syncronization of OIR events between the active and standby

Describe the Stateful Switchover (SSO) mode on a Supervisor Engine.

In SSO mode, the redundant Supervisor Engine starts up in a full initialized state and synchonizes with the startup and running configuration of the active Supervisor Engine. The standby in SSO mode also keeps in sync with the active for all changes in hardware and software starts for features that are supported via SSO.

What is a benefit of using a 6500 series switch over a 4500 series during an SSO failover?

On a 4500 Catalyst, L3 information needs to be relearned after a Supervisor Engine failover with just the SSO mode of redundancy, but the newly active continues to use existing L2 switching information to continue forwarding traffic until L3 information is relearned.

Describe the benefits of used NSF with SSO redundancy.

NSF with SSO redundancy includes the standard SSO for L2 switching; however, it also minimizes the amount of time that a L3 network is unavailable following a Supervisor Engine switchover by continuing to forward IP packets using CEF entries built from the old active Supervisor.

How does NSF SSO maintain its L3 functionality during a failover?

When using the NSF with SSO feature, the reconvergence of supported L3 routing protocols happens automatically in the background while packet forwarding continues. The standby maintains the copy of the CEF entries from the active, and upon switchover, the new active uses the CEF entries while the routing protocol converges without interruption f user traffic.

How do neighboring routers know that an NSF with SSO failover is still allowing traffic to pass successfully across the network?

Changes have been made to the routing protocols so that upon switchover, an NSF-enabled router sends special packets that trigger routing updates from the NSF-aware neighbors without resetting the peer relationship. NSF-aware routers are not required to be NFS routers themselves.

Describe the use of Single Router Mode (SRM).

SRM is used when more than 1 IOS Supervisor is installed and the router is running CatOS (hybrid mode). By default they both would be active. With SRM, one Supervisor goes active and the other into standby.

What is the benefit of using Cisco IOS Software Modularity and In-Service Software Upgrade (ISSU)?

With Cisco IOS Software Modularity, processes run in their own protected memory space with the Supervisor Engine's main memory. The capability to restart processes also enables patching of these processes at run time.

What command powers up or down a module an a Catalyst 6500 switch?

What command power cycles a module on a Catalyst 6500 switch?

What are some ways that a host can be configured for dynamic router discovery?

- Proxy ARP - The host uses ARP to determine the next-hop MAC address of off-network destinations. Local routers respond to the ARP request with their own MAC address

 

- Routing protocol - The host listens to dynamic routing protocol updates and forms it own routing table

 

- ICMP Router Discover Protocol (IRDP) client -  The host runs an ICMP router discovery client.

How does a Cisco router work as a proxy ARP?

If a router receives an ARP request for a host that is not on the same interface as the ARP request sender, and if the router has all its routes to that host through other interfaces, then it generates a proxy ARP reply packet giving its own local MAC address. The host that sent the ARP request then sends its packets to the router, which forwards them to the intended host. 

What is IRDP and what is it used for?

IRDP is an extension to ICMP that provides a machanism for routers to advertise useful default routes. A host listens for hello mulitcast messages form the preferred default router, which are only valid for a predefined time. If no new advertisment is not seen, then the default gateway is considered invalid.

What does an HSRP standby group consist of?

- One active router - The active router forwards traffic destined to the virtual IP address.

 

- One standby router - The standby router is the backup router in case the active router fails for the subnet.

 

- One virtual router - The virtual router is the concept of the entire HSRP group acting as 1 virtual router.

 

- Additional HSRP member routers - These routers monitor the current active and standby routers and transition into one of those roles if the current router fails for the subnet. 

What are the different HSRP states that a router may exist in?

- Initial state - This is the stating state of HSRP and indicates that HSRP is not yet fully operational.

 

- Learn state - The router has not determined the virtual IP address and has not yet seen a hello message from the active router.

 

- Listen state - The router knows the virtual IP address but is neither the active nor the standby router.

 

-  Speak state - HSRP routers send periodic message and actively participate in the election of the active or standby router

 

- Standby state - The HSRP router is a candidate to become the next active and sends periodic hello messages

 

- Active state -  The router is currently forwarding packets that are sent to the virtual MAC and IP address of the HSRP group.

How is the virtual MAC address of the HSRP virtual interface determined?

What command configures a router as a member of an HSRP standby group?

What command sets the priority value of a router in an HSRP group?

What command enables a router to resume the active state after a state change?

What command configures the hello time and hold time for a specific HSRP group?

What command configures HSRP tracking on a particular interface?

With HSRP tracking, what is the default value that a tracked interface will decrease its priority by?

The default value is 10

What command displays the status of the HSRP router?

When using VRRP, how is the master virtual router determined?

Because the IP address of the virtual router group is also an IP address on a physical router, the router with that IP address becomes the master virtual router, and receives a priority of 255.

How do VRRP-enabled routers communicate with each other?

The IP number assigned for VRRP is 112. The router that is acting as the VRRP master sends advertisements using this IP number to the multicast address 224.0.0.18, each second by default. The virtual MAC address for the VRRP group is 00-00-5e-00-01-xx, where xx is the VRRP group number in hexadecimal format.

What command defines a VRRP group?

What command defines the VRRP router priority?

How does GLBP differ from VRRP and HSRP?

It allows all group members, known as active virtual forwarders (AVF) to participate in traffic routing. One router in the group, known as the active virtual gateway, responds to all ARP requests for the group. The replies contain the MAC address of one of the other members of the group, depending on how the load is distributed.

What are the different operational modes for load balancing using GLBP?

- Weighted load balancing algorithm - The amount of load directed to an AVF depends on the weighting value advertised by the gateway containing that AVF.

 

- Host-dependent load-balancing algorithm - A host is guaranteed to use the same virtual MAC address as long as that virtual MAC address is participating in the GLBP group.

 

- Round-robin load-balancing algorithm - Each virtual forwarder MAC address takes turns being included in address resolution replies for the virtual IP address. This is the default operational mode.

What command configures an interface as a member of a GLBP group?

What command configures the priority of an GLBP-enabled router?

What command configures the hello and hold timers for a GLBP router?

Briefly describe how Cisco's IOS server load balancing works.

By either using software-based switching or the Cisco Application Control Engine (ACE) service module,a virtual IP handles all requests for a service. The VIP forwards the request to the real servers in a server farm

What are the different modes that Cisco IOS SLB supports?

- Dispatch mode - Each of the real servers is configured with the virtual server address as a loopback address or secondary IP address. The SLB redirects packets to the real servers at the MAC layer, so they must be L2-adjacent to the IOS SLB

 

-  Directed mode - The virtual server can be assigned an IP address that is not known to any of the real servers. IOS SLB translates packets exchanged between a client and a real server, via NAT.

What command is used to define a server farm using IOS SLB?

What command associates the real server with a server farm?

What command enables the real server defined to be used for a Cisco IOS server farm?

What command defines a virtual server when using IOS SLB?

What command configures the IP of a virtual server when using IOS SLB?

What command associates a primary server farm to a virtual server using IOS SLB?

What command speicifies the clients allowed to access the virtual server?

What command shows you stats on the SLB configuration on a switch?