GLBP

GLBP (Gateway Load Balancing Protocol) is a Cisco proprietary protocol needed to make a default gateway redundant. If HSRP can configure only one active router, GLBP can have up to four active routers in the same time. GLBP allows a better traffic balance than HSRP or VRRP.

Glbp_topology The high priority GLBP node becames Active Virtual Gateway (AVG). The second one with high prioriety became AVG Standby. The AVG answers to the ARP requests made by client, assigning them the Virtual MAC (vMAC). Each vMAC is assigned to an Active Virtual Forwarder (AVF). An AVF is an active router configured with GLBP. AVG and AVG Standby routers are AVF too. All AVF routers listen to each other: if one AVF fails, the vMAC is reassigned to another AVF. The GLBP configuration needs a numeric group and the virtual ip address: ~~~ glbp 1 ip 192.168.10.254 ~~~ Authentication can be configured to enhance security: ~~~ glbp 1 authentication md5 key-string CCIE ~~~ At this point GLBP is already working. The MAC address 0007.b400.0101 is a vMAC; another three vMAC are availabl for future nodes: ~~~ R1#show glbp brief Interface Grp Fwd Pri State Address Active router Standby router Et0/0 1 - 100 Active 192.168.10.254 local unknown Et0/0 1 1 - Active 0007.b400.0101 local - ~~~ Adding two more routers, one of them bacame AVG Standby: ~~~ R1#show glbp brief Interface Grp Fwd Pri State Address Active router Standby router Et0/0 1 - 100 Active 192.168.10.254 local 192.168.10.3 Et0/0 1 1 - Active 0007.b400.0101 local - Et0/0 1 2 - Listen 0007.b400.0102 192.168.10.2 - Et0/0 1 3 - Listen 0007.b400.0103 192.168.10.3 - ~~~ ~~~ R2#show glbp brief Interface Grp Fwd Pri State Address Active router Standby router Et0/0 1 - 100 Listen 192.168.10.254 192.168.10.1 192.168.10.3 Et0/0 1 1 - Listen 0007.b400.0101 192.168.10.1 - Et0/0 1 2 - Active 0007.b400.0102 local - Et0/0 1 3 - Listen 0007.b400.0103 192.168.10.3 - ~~~ ~~~ R3#show glbp brief Interface Grp Fwd Pri State Address Active router Standby router Et0/0 1 - 100 Standby 192.168.10.254 192.168.10.1 local Et0/0 1 1 - Listen 0007.b400.0101 192.168.10.1 - Et0/0 1 2 - Listen 0007.b400.0102 192.168.10.2 - Et0/0 1 3 - Active 0007.b400.0103 local - ~~~ R1 is the AVG (first line), the assigned vMAC is 0007.b400.0101. R3 is the AVG Standby, with the vMAC 0007.b400.0103. R2 is an AVF node with the vMAC 0007.b400.0102. The priority is the router priority where the "show" command is typed. Each router can configure the priority and the weight: ~~~ glbp 1 priority 150 glbp 1 preempt glbp 1 weighting 50 ~~~ The R1 weigth is configured as 50, R2's weight as 20 and R3's weight as 20. In this example 50% of traffic will flows through R1, 30% through R2 and 20% through R3. Mind that weigth is not a percent value, but if sum of all weights is 100, then weight can supposed to be a percent value. ~~~ R1#show glbp Ethernet0/0 - Group 1 State is Active 1 state change, last state change 00:32:30 Virtual IP address is 192.168.10.254 Hello time 3 sec, hold time 10 sec Next hello sent in 0.832 secs Redirect time 600 sec, forwarder timeout 14400 sec Authentication MD5, key-string Preemption enabled, min delay 0 sec Active is local Standby is 192.168.10.2, priority 120 (expires in 9.440 sec) Priority 150 (configured) Weighting 5 (configured 5), thresholds: lower 1, upper 5 Load balancing: round-robin Group members: aabb.cc00.0100 (192.168.10.1) local aabb.cc00.0200 (192.168.10.2) authenticated aabb.cc00.0300 (192.168.10.3) authenticated There are 3 forwarders (1 active) Forwarder 1 State is Active 1 state change, last state change 00:32:19 MAC address is 0007.b400.0101 (default) Owner ID is aabb.cc00.0100 Redirection enabled Preemption enabled, min delay 30 sec Active is local, weighting 50 Forwarder 2 State is Listen MAC address is 0007.b400.0102 (learnt) Owner ID is aabb.cc00.0200 Redirection enabled, 599.456 sec remaining (maximum 600 sec) Time to live: 14399.456 sec (maximum 14400 sec) Preemption enabled, min delay 30 sec Active is 192.168.10.2 (primary), weighting 30 (expires in 10.432 sec) Forwarder 3 State is Listen MAC address is 0007.b400.0103 (learnt) Owner ID is aabb.cc00.0300 Redirection enabled, 597.472 sec remaining (maximum 600 sec) Time to live: 14397.472 sec (maximum 14400 sec) Preemption enabled, min delay 30 sec Active is 192.168.10.3 (primary), weighting 20 (expires in 9.184 sec) ~~~ A weigthing interval can be configured: ~~~ glbp 1 weighting 20 lower 15 upper 20 glbp 1 weighting track 1 decrement 10 ~~~ ~~~ R1#show glbp brief Interface Grp Fwd Pri State Address Active router Standby router Et0/0 1 - 150 Active 192.168.10.254 local 192.168.10.2 Et0/0 1 1 - Active 0007.b400.0101 local - Et0/0 1 2 - Listen 0007.b400.0102 192.168.10.2 - Et0/0 1 3 - Listen 0007.b400.0103 192.168.10.2 - ~~~ In the above axample R3 leaves the active mode because the corrent weigth (10) is lower than the minimum acceptavble value (15). R2 took the R3 vMAC.

Posted on 14 Sep 2013 by Andrea.
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