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467 Views 1 Reply Latest reply: May 7, 2012 9:52 AM by Vijay Swaminathan RSS

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Few Clarification on GLBP

May 4, 2012 10:32 AM

Vijay Swaminathan 491 posts since
Aug 29, 2008

Hi Experts,

 

I would need some clarity on GLBP : I have the topology as R1 -----R 2-------R3:

 

R3 is the AVG, R2 is standby AVG and R1 is in Listen state:

 

The output , and the configuration of R1, R2 and R3 are as follows:

 

R1:

===

interface FastEthernet0/0

ip address 10.10.123.1 255.255.255.0

glbp 1 ip 10.10.123.100

glbp 1 priority 110

glbp 1 preempt

glbp 1 weighting 10

glbp 1 load-balancing weighted

 

R1#sh glbp brief

Interface   Grp  Fwd Pri State    Address         Active router   Standby router

Fa0/0       1    -   110 Listen   10.10.123.100   10.10.123.3     10.10.123.2

Fa0/0       1    1   -   Active   0007.b400.0101  local           -

Fa0/0       1    2   -   Listen   0007.b400.0102  10.10.123.2     -

Fa0/0       1    3   -   Listen   0007.b400.0103  10.10.123.3     -

 

 

R2:

====

interface FastEthernet0/0

ip address 10.10.123.2 255.255.255.0

glbp 1 ip 10.10.123.100

glbp 1 priority 120

glbp 1 preempt

glbp 1 weighting 8

glbp 1 load-balancing weighted

 

 

R2#sh glbp brief

Interface   Grp  Fwd Pri State    Address         Active router   Standby router

Fa0/0       1    -   120 Standby  10.10.123.100   10.10.123.3     local

Fa0/0       1    1   -   Listen   0007.b400.0101  10.10.123.1     -

Fa0/0       1    2   -   Active   0007.b400.0102  local           -

Fa0/0       1    3   -   Listen   0007.b400.0103  10.10.123.3     -

 

R3:

===

 

R3#sh run int fa0/0

interface FastEthernet0/0

ip address 10.10.123.3 255.255.255.0

duplex auto

speed auto

glbp 1 ip 10.10.123.100

glbp 1 priority 130

glbp 1 preempt

glbp 1 weighting 1

glbp 1 load-balancing weighted

 

R3#sh glbp brief

Interface   Grp  Fwd Pri State    Address         Active router   Standby router

Fa0/0       1    -   130 Active   10.10.123.100   local           10.10.123.2

Fa0/0       1    1   -   Listen   0007.b400.0101  10.10.123.1     -

Fa0/0       1    2   -   Listen   0007.b400.0102  10.10.123.2     -

Fa0/0       1    3   -   Active   0007.b400.0103  local           -

R3#

 

My Understanding is:

 

1. AVG (R3) since AVG receives the Broadcast ARP request from the client and answers with the VMAC based on the Load Balancing algorithm configured (in this case weighted).

2. as per the diagram, R3 is responsible for VMAC 0007.b400.0103 , R2 for 0007.b400.0102 and R1 for 0007.b400.0101

 

Now Testing:

 

When the AVG fails:

************************

 

When the AVG fails, then R2 takes over as standby.

 

I'm trying to understand the process behind this from the debug messages:

 

ON R2:

 

R2#

*Mar  1 01:37:54.571: GLBP: Fa0/0 1.3 Ignoring Hello (135/10.10.123.1 < 167/10.10.123.3)

*Mar  1 01:37:54.591: GLBP: Fa0/0 1 Standby: g/Active timer expired (10.10.123.3)

*Mar  1 01:37:54.591: GLBP: Fa0/0 1 Active router IP is local, was 10.10.123.3

*Mar  1 01:37:54.591: GLBP: Fa0/0 1 Standby router is unknown, was local

*Mar  1 01:37:54.591: GLBP: Fa0/0 1 Standby -> Active

*Mar  1 01:37:54.591: %GLBP-6-STATECHANGE: FastEthernet0/0 Grp 1 state Standby -> Active

*Mar  1 01:37:54.595: GLBP: Fa0/0 1.3 Listen: g/Active timer expired

*Mar  1 01:37:54.595: GLBP: Fa0/0 1.3 Listen -> Active

R2#

*Mar  1 01:37:54.595: %GLBP-6-FWDSTATECHANGE: FastEthernet0/0 Grp 1 Fwd 3 state Listen -> Active

R2#

R2#

*Mar  1 01:38:04.627: GLBP: Fa0/0 1 Standby router is 10.10.123.1

R2#

 

My understanding and Questions are:

 

1. R2 received hello from R1 and compared the priority.

2. Active Timer expired. that is it did not hear from Active.

3. Now it has taken the role of Active. it was R3 earlier

4. Standby is still unknown (calculation in progress)

5 & 6. Standby to Active Transitions.

7, 8 and 9. What is this message telling ???? Is this about the AVF ??

 

Debug Messages on R1:

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

 

R1#

*Mar  1 01:37:55.703: GLBP: Fa0/0 1 Listen: g/Active timer expired (10.10.123.3)

*Mar  1 01:37:55.703: GLBP: Fa0/0 1 Active router IP is unknown, was 10.10.123.3

*Mar  1 01:37:55.703: GLBP: Fa0/0 1 Listen -> Speak

*Mar  1 01:37:55.707: GLBP: Fa0/0 1.3 Listen: g/Active timer expired

*Mar  1 01:37:55.707: GLBP: Fa0/0 1.3 Listen -> Active

*Mar  1 01:37:55.707: %GLBP-6-FWDSTATECHANGE: FastEthernet0/0 Grp 1 Fwd 3 state Listen -> Active

*Mar  1 01:37:55.759: GLBP: Fa0/0 1 Active router IP is 10.10.123.2

*Mar  1 01:37:55.763: GLBP: Fa0/0 1 Standby router is unknown, was 10.10.123.2

*Mar  1 01:37:55.763: GLBP: Fa0/0 1.3 Active: i/Hello rcvd from higher pri Active router (135/10.10.123.2)

*Mar  1 01:37:55.763: GLBP: Fa0/0 1.3 Active -> Listen

R1#

*Mar  1 01:37:55.767: %GLBP-6-FWDSTATECHANGE: FastEthernet0/0 Grp 1 Fwd 3 state Active -> Listen

R1#

*Mar  1 01:38:03.183: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.123.3 (FastEthernet0/0) is down: holding time expired

R1#

*Mar  1 01:38:05.703: GLBP: Fa0/0 1 Speak: f/Standby timer expired (unknown)

*Mar  1 01:38:05.703: GLBP: Fa0/0 1 Standby router is local

*Mar  1 01:38:05.703: GLBP: Fa0/0 1 Speak -> Standby

R1#

 

My understanding as per debug lines:

1 & 2. Active Timer Expired. (lost connection with AVG)

3. Now from AVG listen state it starts moving to speak state

4 - 11 . My understanding is: from Listen it goes into Active AVG then it hears about a higher priority from R2 and then goes back from Active back again to Listen.

12. When R2 (earlier standby) moved to active, then standby hold timer would have kicked off and the line 12 talks about the expiry of that time.

13 - 14 : This finally tells who the standby is:

 

Another question is:


for the VMAC 0007.b400.0103 for which R3 was active, somebody should take over as active for this VMAC. it should be either R1 or R2.. on what basis is this decision made ??


and where are those pertinent messages???



please advice:

 

Thanks

-Vijay

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