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GLBP Question

Hi, I just want to clarify GLBP config on one of our VLAN after our main WAN link went down. We used 2 6506s as our core:

Primary:

Vlan20 - Group 20

State is Active

2 state changes, last state change 29w2d

Virtual IP address is 10.80.104.1

Hello time 3 sec, hold time 10 sec

Next hello sent in 0.096 secs

Redirect time 600 sec, forwarder time-out 14400 sec

Preemption enabled, min delay 0 sec

Active is local

Standby is 10.80.104.3, priority 254 (expires in 7.580 sec)

Priority 255 (configured)

Weighting 90, low (configured 110), thresholds: lower 95, upper 105

Track object 20 state Down decrement 20

Load balancing: weighted

There are 2 forwarders (0 active)

Forwarder 1

State is Listen

680 state changes, last state change 00:25:44

MAC address is 0007.b400.1401 (default)

Owner ID is 0015.2ce0.d800

Redirection enabled

Preemption enabled, min delay 30 sec

Active is 10.80.104.3 (secondary), weighting 110 (expires in 7.580 sec)

Arp replies sent: 16973696

Forwarder 2

State is Listen

14 state changes, last state change 5d17h

MAC address is 0007.b400.1402 (learnt)

Owner ID is 0015.2ce0.dc00

Redirection enabled, 599.932 sec remaining (maximum 600 sec)

Time to live: 14399.932 sec (maximum 14400 sec)

Preemption enabled, min delay 30 sec

Active is 10.80.104.3 (primary), weighting 110 (expires in 9.932 sec)

Arp replies sent: 16975045

_____________________________________

Secondary:

Vlan20 - Group 20

State is Standby

5 state changes, last state change 29w2d

Virtual IP address is 10.80.104.1

Hello time 3 sec, hold time 10 sec

Next hello sent in 2.948 secs

Redirect time 600 sec, forwarder time-out 14400 sec

Preemption enabled, min delay 0 sec

Active is 10.80.104.2, priority 255 (expires in 9.464 sec)

Standby is local

Priority 254 (configured)

Weighting 110 (configured 110), thresholds: lower 95, upper 105

Track object 20 state Up decrement 20

Load balancing: weighted

There are 2 forwarders (2 active)

Forwarder 1

State is Active

1 state change, last state change 00:25:50

MAC address is 0007.b400.1401 (learnt)

Owner ID is 0015.2ce0.d800

Time to live: 12849.216 sec (maximum 14400 sec)

Preemption enabled, min delay 30 sec

Active is local, weighting 110

Forwarder 2

State is Active

15 state changes, last state change 5d17h

MAC address is 0007.b400.1402 (default)

Owner ID is 0015.2ce0.dc00

Preemption enabled, min delay 30 sec

Active is local, weighting 110

Questions:

1. Why are there 2 forwarders? Two devices configured for GLBP?

2. What is the difference between the MAC address and Owner ID?

3. Why is it on the primary vlan group 20 is active? Should it be in a standby state because that's the device where the link failed?

4. Does GLBP use 0007.b400.14xx pool of MAC addresses to be assigned to AVFs?

5. Why there is no indicator/status which state that it's the AVG?

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: GLBP Question

Hello John,

review GLBP

http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_glbp.html

1) GLBP L=load-balancing so there is the concept of multiple forwarders within a single group is the reason for this protocol existance.

2) GLBP Virtual MAC Address Assignment

A GLBP group allows up to four virtual MAC addresses per group. The AVG is responsible for assigning the virtual MAC addresses to each member of the group. Other group members request a virtual MAC address after they discover the AVG through hello messages. Gateways are assigned the next MAC address in sequence. A virtual forwarder that is assigned a virtual MAC address by the AVG is known as a primary virtual forwarder. Other members of the GLBP group learn the virtual MAC addresses from hello messages. A virtual forwarder that has learned the virtual MAC address is referred to as a secondary virtual forwarder.

3) because in GLBP there are two dimensions: priority and weighting and tracking has reduced the weighting value:

Priority 255 (configured)

Weighting 90, low (configured 110), thresholds: lower 95, upper 105

Track object 20 state Down decrement 20

4)

yes up to 4 for a group:

0007.b400.0101 for group 1

The function of the AVG is that it assigns a virtual MAC address to each member of the GLBP group. Each gateway assumes responsibility for forwarding packets sent to the virtual MAC address assigned to it by the AVG. These gateways are known as active virtual forwarders (AVFs) for their virtual MAC address

5) AVG state is given by Active / Standby

but traffic is forwarded by forwarders.

Hope to help

Giuseppe

2 REPLIES
Hall of Fame Super Silver

Re: GLBP Question

Hello John,

review GLBP

http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_glbp.html

1) GLBP L=load-balancing so there is the concept of multiple forwarders within a single group is the reason for this protocol existance.

2) GLBP Virtual MAC Address Assignment

A GLBP group allows up to four virtual MAC addresses per group. The AVG is responsible for assigning the virtual MAC addresses to each member of the group. Other group members request a virtual MAC address after they discover the AVG through hello messages. Gateways are assigned the next MAC address in sequence. A virtual forwarder that is assigned a virtual MAC address by the AVG is known as a primary virtual forwarder. Other members of the GLBP group learn the virtual MAC addresses from hello messages. A virtual forwarder that has learned the virtual MAC address is referred to as a secondary virtual forwarder.

3) because in GLBP there are two dimensions: priority and weighting and tracking has reduced the weighting value:

Priority 255 (configured)

Weighting 90, low (configured 110), thresholds: lower 95, upper 105

Track object 20 state Down decrement 20

4)

yes up to 4 for a group:

0007.b400.0101 for group 1

The function of the AVG is that it assigns a virtual MAC address to each member of the GLBP group. Each gateway assumes responsibility for forwarding packets sent to the virtual MAC address assigned to it by the AVG. These gateways are known as active virtual forwarders (AVFs) for their virtual MAC address

5) AVG state is given by Active / Standby

but traffic is forwarded by forwarders.

Hope to help

Giuseppe

Re: GLBP Question

i'm enlightened now. thanks!

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