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This chapter contains the following sections:
Your software release might not support all the features documented in this module. For the latest caveats and feature information, see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "New and Changed Information"chapter or the Feature History table in this chapter.
Gateway Load Balancing Protocol (GLBP) provides path redundancy for IP by sharing protocol and Media Access Control (MAC) addresses between redundant gateways. Additionally, GLBP allows a group of Layer 3 routers to share the load of the default gateway on a LAN. A GLBP router can automatically assume the forwarding function of another router in the group if the other router fails.
GLBP provides automatic gateway backup for IP hosts configured with a single default gateway on an IEEE 802.3 LAN. Multiple routers on the LAN combine to offer a single virtual first-hop IP gateway while sharing the IP packet forwarding load. Other routers on the LAN might act as redundant GLBP gateways that become active if any of the existing forwarding gateways fail.
GLBP performs a similar function to the Hot Standby Redundancy Protocol (HSRP) and the Virtual Router Redundancy Protocol (VRRP). HSRP and VRRP allow multiple routers to participate in a virtual group configured with a virtual IP address. These protocols elect one member as the active router to forward packets to the virtual IP address for the group. The other routers in the group are redundant until the active router fails.
GLBP performs an additional load balancing function that the other protocols do not provide. GLBP load balances over multiple routers (gateways) using a single virtual IP address and multiple virtual MAC addresses. GLBP shares the forwarding load among all routers in a GLBP group instead of allowing a single router to handle the whole load while the other routers remain idle. You configure each host with the same virtual IP address, and all routers in the virtual group participate in forwarding packets. GLBP members communicate between each other using periodic hello messages.
GLBP prioritizes gateways to elect an active virtual gateway (AVG). If multiple gateways have the same priority, the gateway with the highest real IP address becomes the AVG. The AVG assigns a virtual MAC address to each member of the GLBP group. Each member is the active virtual forwarder (AVF) for its assigned virtual MAC address, forwarding packets sent to its assigned virtual MAC address.
The AVG also answers Address Resolution Protocol (ARP) requests for the virtual IP address. Load sharing is achieved when the AVG replies to the ARP requests with different virtual MAC addresses.
 Note |
Packets received on a routed port destined for the GLBP virtual IP address terminate on the local router, regardless of whether that router is the active GLBP router or a redundant GLBP router. This termination includes ping and Telnet traffic. Packets received on a Layer 2 (VLAN) interface destined for the GLBP virtual IP address terminate on the active router. |
The AVG assigns the virtual MAC addresses to each member of the group. The group members request a virtual MAC address after they discover the AVG through hello messages. The AVG assigns the next MAC address based on the load-balancing algorithm selected. A gateway that is assigned with a virtual MAC address by the AVG is the primary virtual forwarder. The other members of the GLBP group that learn the virtual MAC addresses from hello messages are secondary virtual forwarders.
GLBP provides virtual gateway redundancy. A member in a group can be in the active, standby, or listen state. GLBP uses a priority algorithm to elect one gateway as the AVG and elect another gateway as the standby virtual gateway. The remaining gateways go into the listen state. You can configure the GLBP priority on each gateway. If the GLBP priority is identical on multiple gateways, GLBP uses the gateway with the highest IP address as the AVG.
If an AVG fails, the standby virtual gateway assumes responsibility for the virtual IP address. GLBP elects a new standby virtual gateway from the gateways in the listen state.
GLBP provides virtual forwarder redundancy. Virtual forwarder redundancy is similar to virtual gateway redundancy with an active virtual forwarder (AVF). If the AVF fails, a secondary virtual forwarder in the listen state assumes responsibility for the virtual MAC address. This secondary virtual forwarder is also a primary virtual forwarder for a different virtual MAC address. GLBP migrates hosts away from the old virtual MAC address of the failed AVF, using the following two timers:
Redirect timer—Specifies the interval during which the AVG continues to redirect hosts to the old virtual MAC address. When the redirect time expires, the AVG stops using the old virtual MAC address in ARP replies, although the secondary virtual forwarder continues to forward packets that were sent to the old virtual MAC address.
Secondary hold timer—Specifies the interval during which the virtual MAC address is valid. When the secondary hold time expires, GLBP removes the virtual MAC address from all gateways in the GLBP group and load balances the traffic over the remaining AVFs. The expired virtual MAC address becomes eligible for reassignment by the AVG.
GLBP uses hello messages to communicate the current state of the timers.
In the figure, router A is the AVG for a GLBP group and is responsible for the virtual IP address 192.0.2.1. Router A is also an AVF for the virtual MAC address 0007.b400.0101. Router B is a member of the same GLBP group and is designated as the AVF for the virtual MAC address 0007.b400.0102. Client 1 has a default gateway IP address of 192.0.2.1, the virtual IP address, and a gateway MAC address of 0007.b400.0101 that points to router A. Client 2 shares the same default gateway IP address but receives the gateway MAC address 0007.b400.0102 because router B is sharing the traffic load with router A.
If router A becomes unavailable, client 1 does not lose access to the WAN because router B assumes responsibility for forwarding packets sent to the virtual MAC address of router A and for responding to packets sent to its own virtual MAC address. Router B also assumes the role of the AVG for the entire GLBP group. Communication for the GLBP members continues despite the failure of a router in the GLBP group.
GLBP has three authentication types:
MD5 authentication
Plain text authentication
No authentication
MD5 authentication provides greater security than plain text authentication. MD5 authentication allows each GLBP group member to use a secret key to generate a keyed MD5 hash that is part of the outgoing packet. At the receiving end, a keyed hash of an incoming packet is generated. If the hash within the incoming packet does not match the generated hash, the packet is ignored. The key for the MD5 hash can either be given directly in the configuration using a key string or supplied indirectly through a key chain.
You can also choose to use a simple password in plain text to authenticate GLBP packets, or choose no authentication for GLBP.
GLBP rejects packets in any of the following cases:
The authentication schemes differ on the router and in the incoming packet.
MD5 digests differ on the router and in the incoming packet.
Text authentication strings differ on the router and in the incoming packet.
You can configure the following load-balancing methods for GLBP:
Round-robin—GLBP cycles through the virtual MAC addresses sent in ARP replies, load balancing the traffic across all the AVFs.
Weighted—AVG uses the advertised weight for an AVF to decide the load directed to the AVF. A higher weight means that the AVG directs more traffic to the AVF.
Host dependent—GLBP uses the MAC address of the host to determine which virtual MAC address to direct the host to use. This algorithm guarantees that a host gets the same virtual MAC address if the number of virtual forwarders does not change.
The default for IPv4 networks is round-robin. You can disable all load balancing for GLBP on an interface. If you do not configure load balancing, the AVG handles all traffic for the hosts while the other GLBP group members are in standby or listen mode.
You can configure GLBP to track an interface or routes and enable the secondary virtual forwarder to take over if a tracked link goes down. GLBP tracking uses weighted load-balancing to determine whether a GLBP group member acts as an AVF. You must configure the initial weighting values and optional thresholds to enable or disable this group member as an AVF. You can also configure the interface to track and the value that reduces the interface’s weighting if the interface goes down. When the GLBP group weighting drops below the lower threshold, the member is no longer an AVF and a secondary virtual forwarder takes over. When the weighting rises above the upper threshold, the member can resume its role as an AVF.
In the figure, the Ethernet 1/2 interface on router 1 is the gateway for host 1 (the AVF for virtual MAC address, vMAC1), while Ethernet 2/2 on router 2 acts as a secondary virtual forwarder for Host 1. Ethernet 1/2 tracks Ethernet 3/1, which is the network connection for router 1. If Ethernet 3/1 goes down, the weighting for Ethernet 1/2 drops to 90. Ethernet 2/2 on router 2 preempts Ethernet 1/2 and takes over as AVF because it has the default weighting of 100 and is configured to preempt the AVF.
GLBP supports high availability through stateful restarts and stateful switchovers. A stateful restart occurs when the GLBP process fails and is restarted. A stateful switchover occurs when the active supervisor switches to the standby supervisor. Cisco NX-OS applies the run-time configuration after the switchover.
If GLBP hold timers are configured for short time periods, these timers might expire during a controlled switchover or in-service software upgrade (ISSU). GLBP supports extended non-stop forwarding (NSF) to temporarily extend these GLBP hold timers during a controlled switchover or ISSU.
With extended NSF configured, GLBP sends hello messages with the extended timers. GLBP peers update their hold timers with these new values. The extended timers prevent unnecessary GLBP state changes during the switchover or ISSU. After the switchover or ISSU event, GLBP restores the hold timers to their original configured values. If the switchover fails, GLBP restores the hold timers after the extended hold timer values expire.
GLBP supports virtual routing and forwarding (VRF) instances. VRFs exist within virtual device contexts (VDCs). By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF.
If you change the VRF membership of an interface, Cisco NX-OS removes all Layer 3 configuration, including GLBP.
For more information, see the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide.
GLBP has the following prerequisites:
Globally enable the GLBP feature.
You can only configure GLBP on Layer 3 interfaces (see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, and the Interfaces Configuration Guide, Cisco DCNM for LAN).
If you configure VDCs, install the Advanced Services license and enter the desired VDC (see the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide.
GLBP has the following configuration guidelines and limitations:
You should configure all customization options for GLBP on all GLBP member gateways before enabling a GLBP group by configuring a virtual IP address.
You must configure an IP address for the interface that you configure GLBP on and enable that interface before GLBP becomes active.
The GLBP virtual IP address must be in the same subnet as the interface IP address.
We recommend that you do not configure more than one first-hop redundancy protocol on the same interface.
Cisco NX-OS removes all Layer 3 configuration on an interface when you change the VDC, interface VRF membership, port channel membership, or when you change the port mode to Layer 2.
Cisco NX-OS does not support GLBP group configuration on interface secondary subnets.
Cisco NX-OS does not support GLBP for IPv6.
The GLBP does not support gratuitous ARP by design.
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
|
Parameters |
Default |
|---|---|
|
Authentication |
No authentication |
|
Extended hold timer |
10 seconds |
|
Forwarder preemption delay |
30 seconds |
|
Forwarder timeout |
14400 seconds |
|
Hello timer |
3 seconds |
|
Hold timer |
10 seconds |
|
GLBP feature |
Disabled |
|
Load balancing |
Round robin |
|
Preemption |
Disabled |
|
Priority |
100 |
|
Redirect timer |
600 seconds |
|
Weighting |
100 |
Configuring GLBP
You must enable GLBP before you can configure and enable any GLBP groups.
Ensure that you are in the correct VDC (or use the switchto vdc command).
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# [no] feature glbp |
Enables GLBP. |
switch# configure terminal
switch(config)# feature glbp
switch(config)# copy running-config startup-config
You can configure GLBP to authenticate the protocol using cleartext or an MD5 digest. MD5 authentication uses a key chain (see the Cisco Nexus 7000 Series NX-OS Security Configuration Guide).
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable GLBP.
Note |
You must configure the same authentication and keys on all members of the GLBP group. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# interface interface-type slot/port |
Enters interface configuration mode. |
|
Step 3 |
switch(config-if)# ip ip-address/length |
Configures the IPv4 address for the interface. |
|
Step 4 |
switch(config-if)# glbp group-number |
Creates a GLBP group and enters GLBP configuration mode. The range is from 0 to 1024. |
|
Step 5 |
switch(config-if-glbp)# authentication text string |
Configures cleartext authentication for GLBP on this interface. |
|
Step 6 |
switch(config-if-glbp)# authentication md5 {key-chain key-chain | key-string {text | encrypted text}} |
Configures MD5 authentication for GLBP on this interface. |
|
Step 7 |
switch(config-if-glbp)# ip [ip-address [secondary]] |
Enables GLBP on an interface and identifies the primary IP address of the virtual gateway. After you identify a primary IP address, you can use the glbp group ip command again with the secondary keyword to indicate additional IP addresses supported by this group. If you only use the ip keyword, GLBP learns the virtual IP address from the neighbors. |
|
Step 8 |
(Optional) switch(config-if-glbp)# show glbp [group group-number] |
(Optional)
Displays GLBP information. |
|
Step 9 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
This example shows how to configure MD5 authentication for GLBP on Ethernet 1/2 after creating the key chain:
switch# configure terminal
switch(config)# key chain glbp-keys
switch(config-keychain)# key 0
switch(config-keychain-key)# key-string 7 zqdest
switch(config-keychain-key) accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008
switch(config-keychain-key) send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008
switch(config-keychain-key) key 1
switch(config-keychain-key) key-string 7 uaeqdyito
switch(config-keychain-key) accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008
switch(config-keychain-key) send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008
switch(config)# interface ethernet 1/2
switch(config-if)# glbp 1
switch(config-if-glbp)# authenticate md5 key-chain glbp-keys
switch(config-if-glbp)# copy running-config startup-configYou can configure GLBP to use load balancing based on round-robin, weighted, or host-dependent methods.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch(config-if)# glbp group-number |
Creates a GLBP group and enters GLBP configuration mode. The range is from 0 to 1024. |
|
Step 2 |
switch(config-if-glbp)# load-balancing [host-dependent | round-robin | weighted] |
Sets the GLBP load-balancing method. The default is round-robin. |
This example shows how to configure load balancing for GLBP:
switch(config-if)# glbp 1
switch(config-if-glbp)# load-balancing weighted
You can configure GLBP weighting values and object tracking to work with the GLBP weighted load-balancing method.
You can optionally configure the interface to preempt an AVF if the interface was originally assigned with the virtual MAC address or if this interface has a higher weight than the AVF.
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable GLBP.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# track object-id interface interface-type number {ip routing | line-protocol} |
Configures the interface that this GLBP interface tracks. Changes in the state of the interface affect the priority of this GLBP interface as follows:
|
|
Step 3 |
switch(config)# track object-id ip route ip-prefix/length reachability |
Creates a tracked object for a route and enters tracking configuration mode. The object-id range is from 1 to 500. |
|
Step 4 |
switch(config)# interface interface-type slot/por |
Enters interface configuration mode. |
|
Step 5 |
switch(config-if)# ip ip-address/length |
Configures the IPv4 address for the interface. |
|
Step 6 |
switch(config-if)# glbp group-number |
Creates a GLBP group and enters GLBP configuration mode. |
|
Step 7 |
switch(config-if-glbp)# weighting maximum [lower lower] [upper upper] |
Specifies the initial weighting value and the upper and lower thresholds for a GLBP gateway. The maximum range is from 1 to 254. The default weighting value is 100. The lower range is from 1 to 253. The upper range is from 1 to 254. |
|
Step 8 |
switch(config-if-glbp)# weighting-track object-number [decrement value] |
Specifies an object to be tracked that affects the weighting of a GLBP gateway. The value argument specifies a reduction in the weighting of a GLBP gateway when a tracked object fails. The range is from 1 to 255. |
|
Step 9 |
(Optional) switch(config-if-glbp)# forwarder preempt [delay minimum seconds] |
(Optional)
Configures the router to take over as AVF for a GLBP group if the current AVF for a GLBP group falls below its low weighting threshold. The range is from 0 to 3600 seconds. This command is enabled by default with a delay of 30 seconds. |
|
Step 10 |
switch(config-if-glbp)# ip [ip-address [secondary]] |
Enables GLBP on an interface and identifies the primary IP address of the virtual gateway. After you identify a primary IP address, you can use the glbp group ip command again with the secondary keyword to indicate additional IP addresses supported by this group. If you only use the ip keyword, GLBP learns the virtual IP address from the neighbors. |
|
Step 11 |
(Optional) switch(config-if-glbp)# show glbp interface-type number |
(Optional)
Displays GLBP information for an interface. |
|
Step 12 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
The following example shows how to configure GLBP weighting and tracking on Ethernet 1/2:
switch# configure terminal
switch(config)# track 2 interface ethernet 2/2 ip routing
switch(config)# interface ethernet 1/2
switch(config-if)# glbp 1
switch(config-if-glbp) weighting 110 lower 95 upper 105
switch(config-if-glbp) weighting track 2 decrement 20
switch(config-if-glbp)# copy running-config startup-configCustomizing the behavior of GLBP is optional. Be aware that as soon as you enable a GLBP group by configuring a virtual IP address, that group is operational. If you enable a GLBP group before you customize GLBP, the router could take over control of the group and become the AVG before you finish customizing the feature. If you plan to customize GLBP, you should do so before enabling GLBP.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch(config-if-glbp)# glbp group-number |
Creates a GLBP group and enters GLBP configuration mode. |
|
Step 2 |
switch(config-if-glbp)# timers [msec] hellotime [msec] holdtime |
Configures the following hello and hold times for this GLBP member:
The optional msec keyword specifies that the argument is expressed in milliseconds, instead of the default seconds. |
|
Step 3 |
switch(config-if-glbp)# timers redirect redirect timeout |
Configures the following timers:
|
|
Step 4 |
switch(config-if-glbp)# priority level |
Sets the priority level used to select the AVG in a GLBP group. The range is from 1 to 255. The default is 100. |
|
Step 5 |
switch(config-if-glbp)# preempt [delay minimum seconds] |
Configures the router to take over as AVG for a GLBP group if it has a higher priority than the current AVG. This command is disabled by default. Use the optional delay minimum keywords and the seconds argument to specify a minimum delay interval in seconds before preemption of the AVG takes place. The seconds range is from 0 to 3600 seconds. The minimum delay default is 3600 seconds. |
The following example shows how to customize GLBP:
switch(config-if)# glbp 1
switch(config-if-glbp)# timers 5 18
switch(config-if-glbp)# timers redirect 600 7200
switch(config-if-glbp)# priority 254
switch(config-if-glbp)# preempt delay minimum 60You can configure GLBP to use extended hold timers to support extended NSF during a controlled (graceful) switchover or ISSU, including software upgrades and supervisor switchovers. You should configure extended hold timers on all GLBP gateways.
Note |
You must configure extended hold timers on all GLBP gateways if you configure non-default extended hold timers. You can configure different extended hold timer values on each GLBP gateway, based on the expected system switchover delays. |
Use the show glbp command to display the extended hold time.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch(config-if)# glbp group-number Example: |
Creates a GLBP group and enters GLBP configuration mode. |
|
Step 2 |
switch(config)# glbp timers extended-hold [timer] |
Sets the GLBP extended hold timer, in seconds. The timer range is from 10 to 255. The default is 10. |
The following example shows how to configure extended hold timers for GLBP:
switch(config-if)# glbp 1
switch(config)# glbp timers extended-hold 30You can configure the virtual IP address on an interface to enable the GLBP group. You must configure each gateway in the GLBP group with the same group number. The GLBP member can learn all other required parameters from another GLBP member.
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable GLBP.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# interface interface-type slot/por |
Enters interface configuration mode. |
|
Step 3 |
switch(config-if)# ip ip-address/length |
Configures the IPv4 address for the interface. |
|
Step 4 |
switch(config-if)# glbp group-number |
Creates a GLBP group and enters GLBP configuration mode. |
|
Step 5 |
switch(config-if-glbp)# ip [ip-address [secondary]] |
Enables GLBP on an interface and identifies the virtual IP address. The virtual IP should be in the same subnet as the interface IP address. After you identify a virtual IP address, you can use the glbp group ip command again with the secondary keyword to indicate additional IP addresses supported by this group. If you only use the ip keyword, GLBP learns the virtual IP address from the neighbors. |
|
Step 6 |
switch(config-if-glbp)# show glbp [group group-number] [brief] |
Displays a brief summary of GLBP information. |
|
Step 7 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
This example shows how to enable GLBP on Ethernet 1/2:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# glbp 1
switch(config-if-glbp)# ip 192.0.2.10To display GLBP configuration information, perform one of the following tasks:
| Command | Purpose |
|---|---|
| show glbp [group group-number] |
Displays the GLBP status for all or one group. |
| show glbp capability |
Displays the GLBP capability for all or one group. |
| show glbp interface interface-type slot/port |
Displays the GLBP status for an interface. |
| show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby] |
Displays the GLBP status for a group or interface for virtual forwarders in the selected state. |
| show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby] brief |
Displays a brief summary of the GLBP status for a group or interface for virtual forwarders in the selected state. |
The following example shows how to enable GLBP on an interface, with MD5 authentication, interface tracking, and weighted load balancing:
key chain glbp-keys
key 0
key-string 7 zqdest
accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008
send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008
key 1
key-string 7 uaeqdyito
accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008
send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008
feature glbp
track 2 interface ethernet 2/2 ip
interface ethernet 1/2
ip address 192.0.2.2/8
glbp 1
authentication md5 key-chain glbp-keys
weighting 110 lower 95 upper 105
weighting track 2 decrement 20
ip 192.0.2.10
no shutdown|
Related Topic |
Document Title |
|---|---|
|
IS-IS CLI commands |
Cisco Nexus 7000 Series NX-OS Unicast Routing Command Reference |
|
VDCs and VRFs |
Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide |
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
This table includes only the updates for those releases that have resulted in additions or changes to the feature.
| Feature Name | Release | Feature Information |
|---|---|---|
|
GLBP |
4.0(1) |
This feature was introduced. |
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