GLBP weighting help

[Andrew White]

Hello,

Can someone explain the GLBP weighting option, I'm struggling with this one.  On my lab set up I have 3 routers and this is all working below, but want to practise using weighting.

R1

track 1 interface FastEthernet0/1 line-protocol

interface FastEthernet0/0

ip address 192.168.1.2 255.255.255.0

duplex auto

speed auto

glbp 1 ip 192.168.1.1

glbp 1 priority 105

glbp 1 preempt

glbp 1 weighting track 1

R2

track 1 interface FastEthernet0/1 line-protocol

interface FastEthernet0/0

ip address 192.168.1.3 255.255.255.0

duplex auto

speed auto

glbp 1 ip 192.168.1.1

glbp 1 priority 104

glbp 1 preempt

glbp 1 weighting track 1

R3

track 1 interface FastEthernet0/1 line-protocol

interface FastEthernet0/0

ip address 192.168.1.4 255.255.255.0

duplex auto

speed auto

glbp 1 ip 192.168.1.1

glbp 1 priority 103

glbp 1 preempt

glbp 1 weighting track 1

So what would it mean it I was to use this on R1:

glbp 1 weighting 100 lower 90 upper 95 (does 100 have to match the 105 prioroity on R1?)

glbp 1 weighting track 1 decrement 20

From what I can see if Fa 0/1 was to go down the GLBP weight would be 105 - 20 = 85 and will no longer be the AVG and AVF and R2 will take over?  If the weight is 95 or above it will become an AVF again and the AVG?

Thanks

[InayathUlla Sharieff]

Hi Adrew,

The example/Configuration part will help you to understand what you are looking for in the blow link;

http://blog.ine.com/2008/04/24/glbp-explained/

if this doesnt help then please let us know and we will try to help you further.

HTH

Regards

Inayath

[Julio Carvajal]

Hello Andrew,

I would say your idea is good but you are wrong in something:

The Weigth attribute will determine only if a router can be an active Virtual forwarder, nothing relatedo to the AVG status.

Based on that we could said that weighting will determine only the capacity that a router has in the GLBP cluster to forward traffic.

glbp 1 weighting 100 lower 90 upper 95 (does 100 have to match the 105 prioroity on R1?)

glbp 1 weighting track 1 decrement 20

In this case we are seing that the weight value is 100 and if the tracking object goes down or fails the weigth will be 80. whitch is lower than 90 so this router will be marked as a non-valid AVF... and finally it will be used back as a AVF until reaches the weighting of 95

The GLBP weight is different than the priority ( this is used to determine the Active virtual gateway)

Regards,

Julio

Remember to rate all of the helpful posts

[Andrew White]

Thanks, I thought all routers in the GLBP cluster were AVF's and the AVG just assigns different virtual mac addresses when a host does an arp lookup?

[InayathUlla Sharieff]

Hi Andrew,

As far the concept goes you are right. In the cluster one of the router will be AVG and other are AVF.

Host request the ARP--> AVG gets it and assign one of the AVF mac address. (It does RR load balancing amount AVF).

HTH

Regards

Inayath

*Plz rate the usefull posts.

[Peter Paluch]

Hello Inayath,

Being a internal Cisco person with access to specifications, could you perhaps also shed more light on this thread which is strongly related to this one? Thank you!

https://supportforums.cisco.com/message/3821065#3821065

In particular, we were discussing how exactly are the AVFs selected from a group of GLBP-enabled routers. Their priorities nor weights do not appear to bear any relevance.

Best regards,

Peter

[Andy White]

Good question Peter I know it is supposed to use round-robin but when I have debugged it didn't seem to follow this process.

Quick question guys, so If I have 3 routers in the GLBP cluster 1 will be the AVG and 2 will be AVF's, does this mean the AVG doesn't forward traffic?

Thanks

[Peter Paluch]

Hello Andy,

If I have 3 routers in the GLBP cluster 1 will be the AVG and 2 will be AVF's, does this mean the AVG doesn't forward traffic?

In reality, one of the routers will be elected AVG and all three routers will be elected AVFs. One of these routers will hence be both AVG and AVF.

Best regards,

Peter