Gateway Load Balancing Protocol

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Gateway Load Balancing Protocol (GLBP) is a Cisco proprietary protocol that attempts to overcome the limitations of existing redundant router protocols by adding basic load balancing functionality.

In addition to being able to set priorities on different gateway routers, GLBP allows a weighting parameter to be set. Based on this weighting (compared to others in the same virtual router group), ARP requests will be answered with MAC addresses pointing to different routers. Thus, load balancing is not based on traffic load, but rather on the number of hosts that will use each gateway router. By default GLBP load balances in round-robin fashion.

GLBP elects one AVG (Active Virtual Gateway) for each group. Other group members act as backup in case of AVG failure. In case there are more than two members, the second best AVG is placed in the Standby state and all other members are placed in the Listening state. This is monitored using hello and holdtime timers, which are 3 and 10 seconds by default. The elected AVG then assigns a virtual MAC address to each member of the GLBP group, including itself, thus enabling AVFs (Active Virtual Forwarders). Each AVF assumes responsibility for forwarding packets sent to its virtual MAC address. There could be up to four AVFs at the same time.

By default, GLBP routers use the local multicast address 224.0.0.102 to send hello packets to their peers every 3 seconds over UDP 3222 (source and destination).

Cisco implemented IPv6 support for GLBP in IOS release 12.2(33)SXI.[1]

  • (Example)Load Balancing
Router1#
 track 1 interface Serial0/0/0.1 ip routing  ! Track 1 is watching Serial0/0/0.1 So it can be weighted.
!
interface GigabitEthernet0/0
 ip address x.x.x.x 255.255.255.0           ! Make sure this IP is in the same network as your Gateway 1 IP.
 ip address x.x.x.x 255.255.255.0 Secondary ! Make sure this IP is in the same network as your Gateway 2 IP.
 glbp 1 ip <Gateway IP>                     ! Your Virtual Gateway IP for Group 1
 glbp 1 weighting 100 lower 91 upper 99     ! Threshold of 91-99 If it fails the weight will drop below 91 and state will be standby
 glbp 1 load-balancing round-robin          ! Distributes Traffic as round-robin, Makes it True Load-balancing.
 glbp 1 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.1
 glbp 2 ip <Gateway IP>                     ! Your Virtual Gateway IP for Group 2
 glbp 2 weighting 100 lower 91 upper 99     ! Threshold of 91-99 If it fails the weight will drop below 91 and state will be standby.
 glbp 2 load-balancing round-robin          ! Distributes Traffic as round-robin, Makes it True Load-balancing.
 glbp 2 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.1
 no ip redirect                             ! Does not redirect traffic if the router has to Resend to sender.
 speed 100
 duplex full
!
Router bgp <ASN>
 Network <Gateway 1 IP> mask 255.255.255.0   ! Virtual Gateway 1 has to be in BGP.
 Network <Gateway 2 IP> mask 255.255.255.0   ! Virtual Gateway 2 has to be in BGP.
Router2#
 track 1 interface Serial0/0/0.1 ip routing ! Track 1 is watching Serial0/0/0.1 So it can be weighted.
!
interface GigabitEthernet0/0
 ip address x.x.x.x 255.255.255.0           ! Make sure this IP is in the same network as your Gateway 1 IP.
 ip address x.x.x.x 255.255.255.0 Secondary ! Make sure this IP is in the same network as your Gateway 2 IP.
 glbp 1 ip <Gateway IP>                     ! Your Virtual Gateway IP for Group 1
 glbp 1 weighting 100 lower 91 upper 99     ! Threshold of 91-99 If it fails the weight will drop below 91 and state will be Standby
 glbp 1 load-balancing round-robin          ! Distributes Traffic as round-robin, Makes it True Load-balancing.
 glbp 1 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.101
 glbp 2 ip <Gateway IP>                     ! Your Virtual Gateway IP for Group 2
 glbp 2 weighting 100 lower 91 upper 99     ! Threshold of 91-99 If it fails the weight will drop below 91 and state will be standby
 glbp 2 load-balancing round-robin          ! Distributes Traffic as round-robin, Makes it True Load-balancing. 
 glbp 2 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.101
 no ip redirect                             ! Does not redirect traffic if the router has to Resend to sender.
 speed 100
 duplex full
!
Router bgp <ASN>
 Network <Gateway 1 IP> mask 255.255.255.0   ! Virtual Gateway 1 has to be in BGP.
 Network <Gateway 2 IP> mask 255.255.255.0   ! Virtual Gateway 2 has to be in BGP.
  • (Example)Load Sharing
  • GLBP weighting has the ability to place a weight on each device when calculating the amount of load sharing that will occur through MAC assignment. Each GLBP router in the group will advertise its weighting and assignment. The AVG will act based on that value.
  • The only reason you would use this is if you have a larger circuit on the primary router than on the backup router. So the higher weight of 160 will take twice as much traffic as the lower weight of 80. If the weights are 120 and 80 respectively, the primary router will take a quarter more traffic than the backup.
track 1 interface Serial0/0/0.1 ip routing  ! Track 1 is watching Serial0/0/0.1 So it can be weighted.
!
interface GigabitEthernet0/0
 ip address x.x.x.x 255.255.255.0           ! Make sure this IP is in the same network as your Virtual Gateway IP.
 glbp 1 ip x.x.x.x                          ! You Virtual Gateway  
 glbp 1 weighting 100 lower 91 upper 99     ! Threshold of 91-99 If it fails the weight will drop below 91 and state will be standby
 glbp 1 load-balancing weighted             ! Will Load Balance according to weight.
 glbp 1 weighting 160                       ! Higher the weight the Higher Priority 
 glbp 1 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.101
 no ip redirect                             ! Does not redirect traffic if the router has to Resend to sender.
 speed 100
 duplex full
 track 1 interface Serial0/0.101 ip routing ! Track 1 is watching Serial0/0/0.101 So it can be weighted.
!
interface GigabitEthernet0/0
 ip address x.x.x.x 255.255.255.0           ! Make sure this IP is in the same network as your Virtual Gateway IP.
 glbp 1 ip x.x.x.x                          ! You Virtual Gateway  
 glbp 1 weighting 100 lower 91 upper 99     ! Range of 91-99 If it fails the weight will drop below 91 and state will be standby
 glbp 1 load-balancing weighted             ! Will Load Balance according to weight.
 glbp 1 weighting 80                        ! Weight is lower on this router, traffic will be directed through the other router
 glbp 1 weighting track 1                   ! The weight is based on the Track 1 interface watching Serial 0/0/0.101
 no ip redirect                             ! Does not redirect traffic if the router has to Resend to sender.
 speed 100
 duplex full

Show GLBP

To display Gateway Load Balancing Protocol (GLBP) information, use the show glbp command in privileged EXEC mode.

show glbp [interface-type interface-number] [group-number] [state] [brief]

The following is sample output from the show glbp command:

Router# show glbp
FastEthernet0/0 - Group 10
  State is Active
    2 state changes, last state change 23:50:33
  Virtual IP address is 10.21.8.10
  Hello time 5 sec, hold time 18 sec
    Next hello sent in 4.300 secs
  Redirect time 600 sec, forwarder time-out 7200 sec
  Authentication MD5, key-string
  Preemption enabled, min delay 60 sec
  Active is local
  Standby is unknown
  Priority 254 (configured)
  Weighting 105 (configured 110), thresholds: lower 95, upper 105
    Track object 2 state Down decrement 5
  Load balancing: host-dependent
  There is 1 forwarder (1 active)
  Forwarder 1
    State is Active
      1 state change, last state change 23:50:15
    MAC address is 0007.b400.0101 (default)
    Owner ID is 0005.0050.6c08
    Redirection enabled
    Preemption enabled, min delay 60 sec
    Active is local, weighting 105

The following is sample output from the show glbp command with the brief keyword specified:

Router# show glbp brief
Interface   Grp  Fwd Pri State    Address         Active router   Standby router
Fa0/0       10   -   254 Active   10.21.8.10       local           unknown       
Fa0/0       10   1   7   Active   0007.b400.0101   local           -

The following is sample output from the show glbp command that displays GLBP group 10:

Router# show glbp 10
FastEthernet0/0 - Group 10
  State is Active
    2 state changes, last state change 23:50:33
  Virtual IP address is 10.21.8.10
  Hello time 5 sec, hold time 18 sec
    Next hello sent in 4.300 secs
  Redirect time 600 sec, forwarder time-out 7200 sec
  Authentication MD5, key-string

  Preemption enabled, min delay 60 sec
  Active is local
  Standby is unknown
  Priority 254 (configured)
  Weighting 105 (configured 110), thresholds: lower 95, upper 105
    Track object 2 state Down decrement 5
  Load balancing: host-dependent
  There is 1 forwarder (1 active)
  Forwarder 1
    State is Active
      1 state change, last state change 23:50:15
    MAC address is 0007.b400.0101 (default)
    Owner ID is 0005.0050.6c08
    Redirection enabled
    Preemption enabled, min delay 60 sec
    Active is local, weighting 105

The following output shows that the redundancy name has been assigned to the "glbp1" group:

Router# show glbp ethernet0/1 1
Ethernet0/1 - Group 1
 State is Listen
   64 state changes, last state change 00:00:54
 Virtual IP address is 10.1.0.7
 Hello time 50 msec, hold time 200 msec
   Next hello sent in 0.030 secs
 Redirect time 600 sec, forwarder time-out 14400 sec
  Authentication text, string "authword"
 Preemption enabled, min delay 0 sec
 Active is 10.1.0.2, priority 105 (expires in 0.184 sec)
 Standby is 10.1.0.3, priority 100 (expires in 0.176 sec)
 Priority 96 (configured)
 Weighting 100 (configured 100), thresholds: lower 95, upper 100
   Track object 1 state Up decrement 10
 Load balancing: round-robin
 IP redundancy name is "glbp1"
  Group members:
   0004.4d83.4801 (10.0.0.0)
   0010.7b5a.fa41 (10.0.0.1)
   00d0.bbd3.bc21 (10.0.0.2) local

The following output shows GLBP support for SSO mode on an active RP:

Router# show glbp 
Ethernet0/0 - Group 1 
State is Standby 
1 state change, last state change 00:00:20 
Virtual IP address is 172.24.1.254 
Hello time 3 sec, hold time 10 sec 
Next hello sent in 0.232 secs 
Redirect time 600 sec, forwarder time-out 14400 sec 
Preemption disabled 
Active is 172.24.1.2, priority 100 (expires in 7.472 sec) 
Standby is local 
Priority 100 (default) 
Weighting 100 (default 100), thresholds: lower 1, upper 100 
Load balancing: round-robin 
Group members: 
aabb.cc00.0100 (172.24.1.1) local 
aabb.cc00.0200 (172.24.1.2) 
There are 2 forwarders (1 active) 
Forwarder 1 
State is Listen 
MAC address is 0007.b400.0101 (learnt) 
Owner ID is aabb.cc00.0200 
Time to live: 14397.472 sec (maximum 14400 sec) 
Preemption enabled, min delay 30 sec 
Active is 172.24.1.2 (primary), weighting 100 (expires in 9.540 sec) 
Forwarder 2 
State is Active 
1 state change, last state change 00:00:28 
MAC address is 0007.b400.0102 (default) 
Owner ID is aabb.cc00.0100 
Preemption enabled, min delay 30 sec 
Active is local, weighting 100

The following output shows GLBP support for SSO mode on a standby RP:

RouterRP-standby# show glbp 

Ethernet0/0 - Group 1 
State is Init (standby RP, peer state is Standby) 
Virtual IP address is 172.24.1.254 
Hello time 3 sec, hold time 10 sec 
Redirect time 600 sec, forwarder time-out 14400 sec 
Preemption disabled 
Active is unknown 
Standby is unknown 
Priority 100 (default) 
Weighting 100 (default 100), thresholds: lower 1, upper 100 
Load balancing: round-robin 
Group members: 
aabb.cc00.0100 (172.24.1.1) local 
aabb.cc00.0200 (172.24.1.2) 
There are 2 forwarders (0 active) 
Forwarder 1 
State is Init (standby RP, peer state is Listen) 
MAC address is 0007.b400.0101 (learnt) 
Owner ID is aabb.cc00.0200 
Preemption enabled, min delay 30 sec 
Active is unknown 
Forwarder 2 
State is Init (standby RP, peer state is Active) 
MAC address is 0007.b400.0102 (default) 
Owner ID is aabb.cc00.0100 
Preemption enabled, min delay 30 sec 
Active is unknown

See also[edit]

External links[edit]

References[edit]

  1. ^ Cisco IOS Software Release 12.2(33)SXI, New Features and Hardware Support