GLBP Configuration

[Thomas Leong]

Hi guys, i stuck in GLBP, assume R8 and R3 line is down.

is it possible to make VPC 2 go from right hand side ? which is VPC2->R2->R4->R3->R9

Remark: R2 & R3 is switch, Load Balancing is using Round-Robin

[Thomas Leong]

or have to configure like this Upper Run in HSRP bottom run in GLBP ?

[Thomas Leong · Accepted solution]

Hi guys, please ignore it, i figure it out answer already, USE Weight haha~ i dont see the button to the delete this topic Thanks

[Georg Pauwen]

Indeed weight is the way to go...

[Giuseppe Larosa · Accepted solution]

Hello @Thomas Leong ,

thanks for your feedback and for sharing the solution.

Be aware that you can mark your own post as a solution to your thread this will increase the visiibility of the thread over time for other users that might have a similar problem.

Best Regards

Giuseppe

[Thomas Leong]

@Giuseppe Larosa @Georg Pauwen  Hi i think i failed already == haha i try using weight, not working. maybe im not very understand the GLBP. if i use weight, do i need to change my glbp load-balancing into Weighted ? or i can keep using round-robin ?

[Giuseppe Larosa]

Hello @Thomas Leong ,

About GLBP tracking and setting thresholds for forwarding capacity of an active forwarder

https://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1040173

GLBP Gateway Weighting and Tracking

GLBP uses a weighting scheme to determine the forwarding capacity of each router in the GLBP group. The weighting assigned to a router in the GLBP group determines whether it will forward packets and, if so, the proportion of hosts in the LAN for which it will forward packets. Thresholds can be set to disable forwarding when the weighting falls below a certain value, and when it rises above another threshold, forwarding is automatically reenabled.

The GLBP group weighting can be automatically adjusted by tracking the state of an interface within the router. If a tracked interface goes down, the GLBP group weighting is reduced by a specified value. Different interfaces can be tracked to decrement the GLBP weighting by varying amounts.

SUMMARY STEPS

1.

enable

2.

configure terminal

3.

track object-number interface type number {line-protocol | ip routing}

4.

interface type number

5.

glbp group weighting maximum [lower lower] [upper upper]

6.

glbp group weighting track object-number [decrement value]

7.

exit

Router(config-if)# glbp 10 weighting track 2 decrement 35

Router(config-if)# glbp 10 weighting 110 lower 95 upper 105

The trick here is to configure a weight decrement so high that when the tracked interface or object  fails the weighting falls down under the lower threshold .

If you are able to do so you can achieve your goal:

! from your initial post in this thread:

Hi guys, i stuck in GLBP, assume R8 and R3 line is down.

is it possible to make VPC 2 go from right hand side ? which is VPC2->R2->R4->R3->R9

>> Remark: R2 & R3 is switch, Load Balancing is using Round-Robin

So my understanding is that GLBP members routers are R8 and R4.

So you need to configure R8 as explained above and it needs to track the interface eth0/0 in such a way that if it fails R8 will not be a virtual forwarder anymore  ( going below the lower threshold).

The remaining device R4 should take over and it should become the Active forwarder on behalf of R8.

This is a key point because GLBP load balancing is based on different ARP replies given to clients by the virtual gateway providing a different virtual forwarder MAC address for the VIP address = default gateway.

So R4 needs to sends out a gratuitos ARP for the Virtual MAC address used by R8.

during the fault R4 will act as AGV, Virtual Forwarder 01 and Virtual Forwader 02.

the client is actually not aware of the direction of the traffic and it will keep to send packets for a destination in a different subnet using the cached ARP entry.

When R8 eth0/0 comes up again R8 can resume its Virtual Forwarder role .

So it is not a question of using round robin versus weighted but to play with weighting , tracking and decrements so that the network can hide failures to the end user devices the clients.

Hope to help

Giuseppe

[Thomas Leong]

@Giuseppe LarosaOps Sir your GIF is missing haha ? maybe reupload once again haha.

[Giuseppe Larosa]

Hello @Thomas Leong ,

you are right the post has not been reviewed.

I usually hand write my posts, this time I tried to do a copy and paste from the configuration guide for lack of time.

So to help you to stop laughing as I would not like you to die for this ,  I report here the reviewed core  message :

Router(config-if)# glbp 10 weighting track 2 decrement 35

Router(config-if)# glbp 10 weighting 110 lower 95 upper 105

The trick here is to configure a weight decrement so high that when the tracked interface or object  fails the weighting falls down under the lower threshold .

If you are able to do so you can achieve your goal:

! from your initial post in this thread:

>> Hi guys, i stuck in GLBP, assume R8 and R3 line is down.

>> is it possible to make VPC 2 go from right hand side ? which is VPC2->R2->R4->R3->R9

>> Remark: R2 & R3 is switch, Load Balancing is using Round-Robin

So my understanding is that GLBP members routers are R8 and R4.

So you need to configure R8 as explained above and it needs to track the interface eth0/0 in such a way that if it fails R8 will not be a virtual forwarder anymore  ( going below the lower threshold).

The remaining device R4 should take over and it should become the Active forwarder on behalf of R8.

This is a key point because GLBP load balancing is based on different ARP replies given to clients by the virtual gateway providing a different virtual forwarder MAC address for the VIP address = default gateway.

So R4 needs to sends out a gratuitos ARP for the Virtual MAC address used by R8.

>> or more appropriately R4 starts to send out GLBP hello messages using also source MAC address = Virtual Forwarder 02 MAC that was owned by R8.

This is needed to inform the LAN switch in the middle that the VF 02 MAC is known out another switch port leading to R4.

during the fault R4 will act as Virtual Forwarder 01 and Virtual Forwader 02 and eventually also as the AVG

the client is actually not aware of the direction of the traffic and it will keep to send packets for a destination in a different subnet using the cached ARP entry.

When R8 eth0/0 comes up again R8 can resume its Virtual Forwarder role and it will send out again GLBP hello messages with source = Virtual Forwarder 02.

This is needed by the LAN switch to update its CAM table.

So it is not a question of using round robin versus weighted but to play with weighting , tracking and decrements so that the network can hide failures to the end user devices the clients.

Hope to help

Giuseppe

[Thomas Leong]

Hi @Giuseppe Larosa i think i understand your answer already and i try myself it work already. But i found out another question to ask you ~ Hope you can guide me thanks ~

Configuration:

[Thomas Leong]

1. No any line is down

R12:

R13:

2. Assume R12 e0/0 is down

R12:

R13:

VPC16

VPC17

@Giuseppe Larosa 

My Question is:

In R13 do show glbp brief, int e0/1 it show standby active active, means my pc cannot send packet from R13 to R11(1.1.1.1) right?

Why my both pc still can ping 1.1.1.1 ya ?

[Thomas Leong]

Hi Sir @Giuseppe Larosa i think i figure it out the problem. Does it correct ?