How is "pri" calculated automatically by GLBP ?

Unanswered Question
Jun 30th, 2008
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Hello.


By using "debug glbp events" can see something like the following

output.



===============================================

GLBP: Fa0/0 123.1 Listen: k/Hello rcvd from lower pri Active router (135/211.102.108.161)

===============================================

or

===============================================

GLBP: Fa0/0 123.1 Active: i/Hello rcvd from higher pri Active router (167/211.102.108.152)

===============================================



Note the (xyz / ip_addr)

Is the "xyz" prior to "ip_addr" the priority of the virtual forwarder?



I wonder how this number "xyz" be calculated by router.

Who knows, please?



Thank you.

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ashok_boin Tue, 07/01/2008 - 02:50
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Hi,


It's not the priority of GLBP which we configured.


I am not sure about 135 or 167 here but what I observed in the labs is...


It says "167" when Primary VF is active & says "135" when Primary VG is inactive.


Pls find the following link which may help...


http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6550/prod_presentation0900aecd801790a3_ps6600_Products_Presentation.html


Regards...

-Ashok.

Pravin Phadte Tue, 07/01/2008 - 02:55
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hi,


xyz is calculated in Weighted Load Balancing Algorithm.


It can be as simple as adding all the weight defined and the sum total will be the xyz.


regards,


pravin

ashok_boin Tue, 07/01/2008 - 06:29
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Pravin,


I don't think this could be sum of all weights as per debugs.


Pls find the conf & debugs here.


PE-1#sh run | in glbp

glbp 1 ip 20.1.1.10

glbp 1 priority 200

glbp 1 weighting 200

glbp 1 load-balancing weighted

PE-1#debug glbp packets

GLBP Packets debugging is on

PE-1#un all

*Mar 1 00:04:58.831: GLBP: Fa0/0 Grp 1 Hello out VG Active pri 200 vIP 20.1.1

.10 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101

*Mar 1 00:04:59.811: GLBP: Fa0/0 Grp 1 Hello in VG Standby pri 50 vIP 20.1.1.

10 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102

All possible debugging has been turned off

PE-1#


-------------------------------------------------


PE-2#sh run | in glbp

*Mar 1 00:23:43.679: %SYS-5-CONFIG_I: Configured from console by console

glbp 1 ip 20.1.1.10

glbp 1 priority 50

glbp 1 weighting 150

glbp 1 load-balancing weighted

PE-2#

*Mar 1 00:04:26.279: GLBP: Fa0/0 Grp 1 Hello in VG Active pri 200 vIP 20.1

.10 hello 3000, hold 10000 VF 1 Active pri 167 vMAC 0007.b400.0101

*Mar 1 00:04:27.115: GLBP: Fa0/0 Grp 1 Hello out VG Standby pri 50 vIP 20.1.

10 hello 3000, hold 10000 VF 2 Active pri 167 vMAC 0007.b400.0102



Irrespective of weight configuration, it's giving 167 as Pri.


Regards...

-Ashok.


Pravin Phadte Tue, 07/01/2008 - 07:55
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Hi Ashok,


I meant to say that weight algorithm is been used by cisco. This does not have any rfc to prove and calculate.


Weighted allows for GLBP to place a weight on each device when calculating the amount of load sharing. For example, if there are two routers in the group, and router A has twice the forwarding capacity of router B, the weighting value should be configured to be double the amount of router B. To assign a weighting value, the glbp x weighting y, where x is the GLBP group number, and y is the weighting value, a number from 1 to 254.


It would be great if some one can come up with and answer

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