As enterprise LANs grow, there becomes a need to break up LANs with routers. Traditionally, routers have performed the layer 3 functionality, but in today’s high-speed LANs there is a need to be able to forward packets much quicker than the traditional routers have been able to. That is where layer 3 switches come into play.

Layer 3 switches can turn on routing by executing the “ip routing” command from the global configuration mode. From there you can create routed interfaces either by using vlan interfaces, which is the likely interface at the distribution layer or on physical Ethernet interfaces by executing the “no switchport” command, then assigning the physical interface an IP Address.

With large networks, topology-based switches may still be too slow. Then you will need to utilize hardwre based layer 3 switching. In hardware based layer 3 switching, the switch can utilize Policy Feature Cards (PFC) and Distributed Feature Cards (DFC) to route traffic at the hardware level. The hardware will do a packet rewrite on the egress port and alter the following fields:

  • Layer 2 (MAC) destination address
  • Layer 2 (MAC) source address
  • Layer 3 IP TTL
  • Layer 3 checksum
  • Layer 2 (MAC) checksum, aka FCS

Any packets that can’t be handled by the hardware will then be sent to the switches MSFC (Multi-Layer Switch Feature Card), which is a software based router.

The switch that uses the PFC, DFC, and MSFC is the Catalyst 6500 switch. Hardware layer 3 switching does not replace routing and routing protocols. It provides IP unicast layer 3 switching locally on each module.

Chassis based switches utilize a centralized forwarding architecture, which enhances LAN performance and can become even better with the use of distributed forwarding as an upgrade.

When CEF (Cisco Express Forwarding) is used a chassis based switch can forward up to 30 mpps per system or when using a dCEF daughter card can deliver 48 mpps sustained throughput per slot.

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HSRP

Hot Standby Routing Protocol, or HSRP, is a Cisco proprietary redundancy routing protocol. It’s typically used in the distribution layer of a LAN. It works is by having two or more layer three devices that communicate with each other via multicast address 224.0.0.2 to UDP port 1985. In a typical configuration there will be a active router and a standby router. Each router has it’s own physical IP Address and they share a virtual IP Address, which hosts on the LAN use as their default gateway. If the standby router detects that the active router is unavailable, then it will assume the active router role by assigning itself the virtual IP Address. There can only be a single active router in an HSRP group, but there can be multiple standby routers.

HSRP has an election process to determine which router is used as the active router. The router configured with the highest HSRP priority is determined to be the active router. In the event of multiple routers with identical priorities, then the router with the highest IP Address wins the active router election.

The preempt option in HSRP enables a router to resume the forwarding router role.

The hello default is 3 seconds and the hold time default is 10 seconds. When changing the default hello and hold times, the hold time would be at least three times the value of the hello timer.

HSRP is defined by RFC 2281.

Active Router Interface Config

interface FastEthernet0/0
ip address 10.10.10.3 255.255.255.0
duplex auto
speed auto
standby 1 ip 10.10.10.1
standby 1 priority 150
standby 1 preempt
end

Active Router show output

host-vlan3#show standby
FastEthernet0/0 - Group 1
State is Active
9 state changes, last state change 00:13:44
Virtual IP address is 10.10.10.1
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.520 secs
Preemption enabled
Active router is local
Standby router is 10.10.10.2, priority 120 (expires in 8.253 sec)
Priority 150 (configured 150)
IP redundancy name is "hsrp-Fa0/0-1" (default)

Standby Router Interface Config

interface FastEthernet0/0
ip address 10.10.10.2 255.255.255.0
duplex auto
speed auto
standby 1 ip 10.10.10.1
standby 1 priority 120
end

Standby Router show output

host-vlan2#show standby
FastEthernet0/0 - Group 1
State is Standby
10 state changes, last state change 00:12:07
Virtual IP address is 10.10.10.1
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 1.476 secs
Preemption disabled
Active router is 10.10.10.3, priority 150 (expires in 7.712 sec)
Standby router is local
Priority 120 (configured 120)
IP redundancy name is "hsrp-Fa0/0-1" (default)

Output from sh ip arp

host-vlan2#show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.2 - 000a.b7e9.8180 ARPA FastEthernet0/0
Internet 10.10.10.3 38 000f.8f6d.ab60 ARPA FastEthernet0/0
Internet 10.10.10.1 0 0000.0c07.ac01 ARPA FastEthernet0/0

In some instances, your routers participating in an HSRP group connect to different devices on their uplinks. If HSRP doesn’t have any method of tracking when there is an uplink failure, then HSRP doesn’t do a very good job of maintaining an active connection to external resources. In those cases, you should implement interface tracking in HSRP. This is done using the “standby 1 track

uplink interface
priority decrement

” command on the HSRP interface.

The “

uplink interface

” is the interface on your router that you want HSRP to monitor it’s status. This interface would connect to the upstream device and probably isn’t participating in HSRP directly. It’s important to want to track the status of the interface so that HSRP can fail over to the other router in the event of a uplink failure.

The “

priority decrement

” is how much HSRP should automatically decrement it’s priority to make the interface go into standby. This value should lower the value enough to no longer be the highest priority in the HSRP group.

Here is the debug output from the standby router going into active mode, as the primary active router becomes unavailable (via the “shut” command on the interface) and then becomes the standby router again.

host-vlan2#debug standby
HSRP debugging is on
*Mar 5 22:12:57.990: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:12:58.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:00.990: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:01.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:03.994: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:04.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:06.994: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:07.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:10.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:13.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:16.186: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:13:16.994: HSRP: Fa0/0 Grp 1 Standby: c/Active timer expired (10.10.10.3)
*Mar 5 22:13:16.994: HSRP: Fa0/0 Grp 1 Active router is local, was 10.10.10.3
*Mar 5 22:13:16.994: HSRP: Fa0/0 Grp 1 Standby router is unknown, was local
*Mar 5 22:13:16.994: HSRP: Fa0/0 Grp 1 Standby -> Active
*Mar 5 22:13:16.994: %HSRP-6-STATECHANGE: FastEthernet0/0 Grp 1 state Standby -> Active
*Mar 5 22:13:16.994: HSRP: Fa0/0 Grp 1 Redundancy "hsrp-Fa0/0-1" state Standby -> Active
*Mar 5 22:13:16.994: HSRP: Fa0/0 Redirect adv out, Active, active 1 passive 1
*Mar 5 22:13:16.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:19.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:19.998: HSRP: Fa0/0 Grp 1 Redundancy group hsrp-Fa0/0-1 state Active -> Active
*Mar 5 22:13:22.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:22.998: HSRP: Fa0/0 Grp 1 Redundancy group hsrp-Fa0/0-1 state Active -> Active
*Mar 5 22:13:25.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:28.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:31.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:34.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:37.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:40.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:43.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:46.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:49.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:51.798: HSRP: Fa0/0 REDIRECT adv in, Passive, active 0, passive 1, from 10.10.10.3
*Mar 5 22:13:52.998: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Active pri 120 vIP 10.10.10.1
*Mar 5 22:13:53.002: HSRP: Fa0/0 REDIRECT adv in, Active, active 1, passive 2, from 10.10.10.3
*Mar 5 22:13:53.002: HSRP: Fa0/0 Grp 1 Coup in 10.10.10.3 Listen pri 150 vIP 10.10.10.1
*Mar 5 22:13:53.002: HSRP: Fa0/0 Grp 1 Active: j/Coup rcvd from higher pri router (150/10.10.10.3)
*Mar 5 22:13:53.002: HSRP: Fa0/0 Grp 1 Active router is 10.10.10.3, was local
*Mar 5 22:13:53.002: HSRP: Fa0/0 Grp 1 Active -> Speak
*Mar 5 22:13:53.002: %HSRP-6-STATECHANGE: FastEthernet0/0 Grp 1 state Active -> Speak
*Mar 5 22:13:53.002: HSRP: Fa0/0 Grp 1 Redundancy "hsrp-Fa0/0-1" state Active -> Speak
*Mar 5 22:13:53.006: HSRP: Fa0/0 Redirect adv out, Passive, active 0 passive 1
*Mar 5 22:13:53.006: HSRP: Fa0/0 API MAC address update
*Mar 5 22:13:53.006: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Speak pri 120 vIP 10.10.10.1
*Mar 5 22:13:53.010: HSRP: Fa0/0 REDIRECT adv in, Active, active 1, passive 1, from 10.10.10.3
*Mar 5 22:13:53.010: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:55.998: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:56.006: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Speak pri 120 vIP 10.10.10.1
*Mar 5 22:13:58.998: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:13:59.006: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Speak pri 120 vIP 10.10.10.1
*Mar 5 22:14:02.002: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:14:02.006: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Speak pri 120 vIP 10.10.10.1
*Mar 5 22:14:03.002: HSRP: Fa0/0 Grp 1 Speak: d/Standby timer expired (unknown)
*Mar 5 22:14:03.002: HSRP: Fa0/0 Grp 1 Standby router is local
*Mar 5 22:14:03.002: HSRP: Fa0/0 Grp 1 Speak -> Standby
*Mar 5 22:14:03.002: HSRP: Fa0/0 Grp 1 Redundancy "hsrp-Fa0/0-1" state Speak -> Standby
*Mar 5 22:14:03.002: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:14:05.002: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:14:06.002: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:14:08.002: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:14:09.002: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:14:11.002: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:14:12.002: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1
*Mar 5 22:14:14.006: HSRP: Fa0/0 Grp 1 Hello in 10.10.10.3 Active pri 150 vIP 10.10.10.1
*Mar 5 22:14:15.002: HSRP: Fa0/0 Grp 1 Hello out 10.10.10.2 Standby pri 120 vIP 10.10.10.1

VRRP

Virtual Routing Redundancy Protocol, or VRRP, serves the same purpose as HSRP, with many of the same features, but is an IEEE standard.

VRRP is defined by RFC 2338.

Master VRRP Router Interface Config

interface FastEthernet0/0
ip address 10.10.10.3 255.255.255.0
duplex auto
speed auto
vrrp 1 ip 10.10.10.1
vrrp 1 priority 150
end

Master VRRP Router sh output

host-vlan3#sh vrrp
FastEthernet0/0 - Group 1
State is Master
Virtual IP address is 10.10.10.1
Virtual MAC address is 0000.5e00.0101
Advertisement interval is 1.000 sec
Preemption is enabled
min delay is 0.000 sec
Priority is 150
Master Router is 10.10.10.3 (local), priority is 150
Master Advertisement interval is 1.000 sec
Master Down interval is 3.414 sec

Backup VRRP Router Interface config

interface FastEthernet0/0
ip address 10.10.10.2 255.255.255.0
duplex auto
speed auto
vrrp 1 ip 10.10.10.1
vrrp 1 priority 120
end

Backup VRRP Router sh output

host-vlan2#sh vrrp
FastEthernet0/0 - Group 1
State is Backup
Virtual IP address is 10.10.10.1
Virtual MAC address is 0000.5e00.0101
Advertisement interval is 1.000 sec
Preemption enabled
Priority is 120
Master Router is 10.10.10.3, priority is 150
Master Advertisement interval is 1.000 sec
Master Down interval is 3.531 sec (expires in 2.683 sec)

Here is the output of the backup vrrp router turning into a master and then backup again.

host-vlan2#debug vrrp
VRRP debugging is on
*Mar 5 22:27:32.954: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:32.954: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:33.958: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:33.958: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:34.958: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:34.958: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:35.958: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:35.962: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:36.962: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:36.962: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:37.962: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:37.962: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:38.966: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:38.966: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:39.966: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:39.966: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:40.970: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:27:40.970: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:27:44.502: VRRP: Grp 1 Event - Master down timer expired
*Mar 5 22:27:44.502: %VRRP-6-STATECHANGE: Fa0/0 Grp 1 state Backup -> Master
*Mar 5 22:27:44.502: VRRP: tbridge_smf_update failed
*Mar 5 22:27:44.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:45.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:46.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:47.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:48.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:49.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:50.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:51.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:52.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:53.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:54.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:55.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:56.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:57.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:58.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:27:59.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:00.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:01.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:02.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:03.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:04.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:05.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:06.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:07.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:08.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:09.502: VRRP: Grp 1 sending Advertisement checksum 52F1
*Mar 5 22:28:09.970: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:09.970: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:28:09.970: %VRRP-6-STATECHANGE: Fa0/0 Grp 1 state Master -> Backup
*Mar 5 22:28:10.970: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:10.970: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:28:11.974: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:11.974: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:28:12.974: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:12.974: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:28:13.974: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:13.974: VRRP: Grp 1 Event - Advert higher or equal priority
*Mar 5 22:28:14.978: VRRP: Grp 1 Advertisement priority 150, ipaddr 10.10.10.3
*Mar 5 22:28:14.978: VRRP: Grp 1 Event - Advert higher or equal priority

It doesn’t appear that VRRP has the ability to perform interface tracking, but could be an option to use in multi-vendor networks.

GLBP

Gateway Load Balancing Protocol, or GLBP, is another Cisco proprietary protocol. It was created with the idea of better utilizing the network resources while still performing the same functionality as HSSRP and VRRP. GLBP performs automatic selection and simultaneous use of multiple available gateways as well as automatic failover in the event of a failure. With HSRP and VRRP, the load balancing and attempt to fully utilize available network resources is a manual process and be burdensome on the network administrator.

GLBP communicates via multicast address 224.0.0.102 to UDP 3222.

Active Router Interface Config

interface FastEthernet0/0
ip address 10.10.10.3 255.255.255.0
duplex auto
speed auto
glbp 1 ip 10.10.10.1
glbp 1 priority 150
glbp 1 preempt
end

Active Router sh output

host-vlan3#sh glbp
FastEthernet0/0 - Group 1
State is Active
2 state changes, last state change 00:08:28
Virtual IP address is 10.10.10.1
Hello time 3 sec, hold time 10 sec
Next hello sent in 1.453 secs
Redirect time 600 sec, forwarder time-out 14400 sec
Preemption disabled
Active is local
Standby is 10.10.10.2, priority 120 (expires in 7.664 sec)
Priority 150 (configured)
Weighting 100 (default 100), thresholds: lower 1, upper 100
Load balancing: round-robin
There are 2 forwarders (1 active)
Forwarder 1
State is Active
1 state change, last state change 00:08:18
MAC address is 0007.b400.0101 (default)
Owner ID is 000f.8f6d.ab60
Redirection enabled
Preemption enabled, min delay 30 sec
Active is local, weighting 100
Forwarder 2
State is Listen
MAC address is 0007.b400.0102 (learnt)
Owner ID is 000a.b7e9.8180
Redirection enabled, 599.343 sec remaining (maximum 600 sec)
Time to live: 14399.343 sec (maximum 14400 sec)
Preemption enabled, min delay 30 sec
Active is 10.10.10.2 (primary), weighting 100 (expires in 9.343 sec)

Active Router sh ip arp output

host-vlan3#sh ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.2 8 000a.b7e9.8180 ARPA FastEthernet0/0
Internet 10.10.10.3 - 000f.8f6d.ab60 ARPA FastEthernet0/0
Internet 10.10.10.1 - 0007.b400.0101 ARPA FastEthernet0/0

Standby Router Interface Config

interface FastEthernet0/0
ip address 10.10.10.2 255.255.255.0
duplex auto
speed auto
glbp 1 ip 10.10.10.1
glbp 1 priority 120
end

Standby Router sh output

host-vlan2#sh glbp
FastEthernet0/0 - Group 1
State is Standby
1 state change, last state change 00:04:17
Virtual IP address is 10.10.10.1
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.836 secs
Redirect time 600 sec, forwarder time-out 14400 sec
Preemption disabled
Active is 10.10.10.3, priority 150 (expires in 8.456 sec)
Standby is local
Priority 120 (configured)
Weighting 100 (default 100), thresholds: lower 1, upper 100
Load balancing: round-robin
There are 2 forwarders (1 active)
Forwarder 1
State is Listen
MAC address is 0007.b400.0101 (learnt)
Owner ID is 000f.8f6d.ab60
Time to live: 14398.452 sec (maximum 14400 sec)
Preemption enabled, min delay 30 sec
Active is 10.10.10.3 (primary), weighting 100 (expires in 8.452 sec)
Forwarder 2
State is Active
1 state change, last state change 00:04:22
MAC address is 0007.b400.0102 (default)
Owner ID is 000a.b7e9.8180
Preemption enabled, min delay 30 sec
Active is local, weighting 100

Standby Router sh ip arp output

host-vlan2#sh ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.2 - 000a.b7e9.8180 ARPA FastEthernet0/0
Internet 10.10.10.3 5 000f.8f6d.ab60 ARPA FastEthernet0/0
Internet 10.10.10.1 - 0007.b400.0102 ARPA FastEthernet0/0

Here is the output from a debug from the standby router. As you can see GLBP load balances by continuously moving the virutal IP Address from one router to the other. You can also see where the standby router becomes active in a failure, then becomes standby again.

host-vlan2#debug glbp
GLBP debugging is on
*Mar 5 22:57:22.550: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:57:24.630: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:25.550: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:57:27.630: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:28.550: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:57:30.630: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:33.630: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:36.630: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:38.554: GLBP: Fa0/0 1 Standby: g/Active timer expired (10.10.10.3)
*Mar 5 22:57:38.554: GLBP: Fa0/0 1 Active router IP is local, was 10.10.10.3
*Mar 5 22:57:38.554: GLBP: Fa0/0 1 Standby router is unknown, was local
*Mar 5 22:57:38.554: GLBP: Fa0/0 1 Standby -> Active
*Mar 5 22:57:38.554: %GLBP-6-STATECHANGE: FastEthernet0/0 Grp 1 state Standby -> Active
*Mar 5 22:57:38.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:38.554: GLBP: Fa0/0 1.1 Listen: g/Active timer expired
*Mar 5 22:57:38.558: GLBP: Fa0/0 1.1 Listen -> Active
*Mar 5 22:57:38.558: %GLBP-6-FWDSTATECHANGE: FastEthernet0/0 Grp 1 Fwd 1 state Listen -> Active
*Mar 5 22:57:38.558: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VF 1 Active pri 135 vMAC 0007.b400.0101
*Mar 5 22:57:41.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:44.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:47.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:50.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:53.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:56.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:57:59.554: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:02.558: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:05.562: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:08.562: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:08.562: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Speak pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:11.562: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Active pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:11.562: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Speak pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:11.566: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:11.566: GLBP: Fa0/0 1 Active router IP is 10.10.10.3, was local
*Mar 5 22:58:11.566: GLBP: Fa0/0 1 Active: k/Hello rcvd from higher pri Active router (150/10.10.10.3)
*Mar 5 22:58:11.566: GLBP: Fa0/0 1 Active -> Speak
*Mar 5 22:58:11.566: %GLBP-6-STATECHANGE: FastEthernet0/0 Grp 1 state Active -> Speak
*Mar 5 22:58:11.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Speak pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:14.562: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:14.570: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Speak pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:17.566: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:17.570: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Speak pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:20.566: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:20.570: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Speak pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:21.566: GLBP: Fa0/0 1 Speak: f/Standby timer expired (unknown)
*Mar 5 22:58:21.566: GLBP: Fa0/0 1 Standby router is local
*Mar 5 22:58:21.566: GLBP: Fa0/0 1 Speak -> Standby
*Mar 5 22:58:21.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:23.566: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:24.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:26.566: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:27.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:29.570: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000
*Mar 5 22:58:30.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 135 vMAC 0007.b400.0101 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:30.570: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:58:30.570: GLBP: Fa0/0 1.1 Active: i/Hello rcvd from higher pri Active router (167/10.10.10.3)
*Mar 5 22:58:30.570: GLBP: Fa0/0 1.1 Active -> Listen
*Mar 5 22:58:30.570: %GLBP-6-FWDSTATECHANGE: FastEthernet0/0 Grp 1 Fwd 1 state Active -> Listen
*Mar 5 22:58:30.570: GLBP: Fa0/0 API MAC address update
*Mar 5 22:58:32.570: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:58:33.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:35.570: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:58:36.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:38.570: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:58:39.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
*Mar 5 22:58:41.574: GLBP: Fa0/0 Grp 1 Hello in 10.10.10.3 VG Active pri 150 vIP 10.10.10.1 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101
*Mar 5 22:58:42.566: GLBP: Fa0/0 Grp 1 Hello out 10.10.10.2 VG Standby pri 120 vIP 10.10.10.1 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102
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