GLBP Load Sharing

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Feb 12th, 2010
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Dear All,


       I have some small problem about GLBP Load Sharing.  I configured GLBP in my network, redundancy is working but load balancing is not working.


I give brief about my network.  I have two ISP, i configure GLBP on both routers and both router link connected to my core Switch 3750.  In core switch i have 5 Vlans configure.  So please can you support me to solve this problem.


Thanks & Regards,

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Ganesh Hariharan Fri, 02/12/2010 - 23:13
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Dear All,


      I have some small problem about GLBP Load Sharing.  I configured GLBP in my network, redundancy is working but load balancing is not working.


I give brief about my network.  I have two ISP, i configure GLBP on both routers and both router link connected to my core Switch 3750.  In core switch i have 5 Vlans configure.  So please can you support me to solve this problem.


Thanks & Regards,


Hi ,


what is the load balancing method configured in GLBP ? If default that is round-robin then  load balancing method where each virtual forwarder in turn is included in address resolution replies for the virtual IP address. This method is the default.


Is your switch is pointing a default route towards vip of glbp ?


and how you have checked that load balancing is not happening.


Ganesh.H

mrsystemengineer Sat, 02/13/2010 - 00:11
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Dear Ganesh,


           I am using host dependent load balancing.  Because i am monitoring with third party tool and i am checking where the traffic is going with my client.  www.whatmyipaddress.com and nat translation also.


so what the problem about load sharing.  I dont know i was check all the configuration about glbp details everything is perfect.  I make route from switch to virtual glbp ip also.


waiting for your reply.



regards,

Ganesh Hariharan Sat, 02/13/2010 - 00:27
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Dear Ganesh,


          I am using host dependent load balancing.  Because i am monitoring with third party tool and i am checking where the traffic is going with my client.  www.whatmyipaddress.com and nat translation also.


so what the problem about load sharing.  I dont know i was check all the configuration about glbp details everything is perfect.  I make route from switch to virtual glbp ip also.


waiting for your reply.



regards,


Hi,


Problem is your load balancing alogorithm which you have configured as host-dependent for glbp whihc means  " load balancing method based on the MAC address of a host where the same forwarder is always used for a particular host while the number of GLBP group members remains unchanged. "


So in your case only one router will be taking the load as traffic is coming from a single mac that is your switch.


Hope that clear


If helpful do rate the post


Ganesh.H

mrsystemengineer Sat, 02/13/2010 - 01:21
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Ganesh,


          i was used for Round robin then weighted at last i was put in host dependent.  i was removed but nothiing is update.  I have vlan on my core switch.  So i need to do anything in switches.  Please if help me in these problem i thanks of you.


regards,

Ganesh Hariharan Sat, 02/13/2010 - 03:00
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Ganesh,


         i was used for Round robin then weighted at last i was put in host dependent.  i was removed but nothiing is update.  I have vlan on my core switch.  So i need to do anything in switches.  Please if help me in these problem i thanks of you.


regards,


Hi,


For your case configure in glbp as round-robin load balancing method where each virtual forwarder in turn is included in address resolution replies for the virtual IP address and it should work and both the routers will reply for virtual ip address.


and load balancing algorithms need to be used depend on environment like Host Dependent is required when an application requires traffic flows to be tracked (for example when using NAT). Round Robin is recommended as the default, it is suitable for all other requirements. Weighted can be used if there are disparities in the capabilities of gateways in the GLBP group. None provides no load balancing.


Hope to help


Ganesh.H

Giuseppe Larosa Sat, 02/13/2010 - 04:48
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Hello Mrsystemengineer,

because you have only one client GLBP load balancing is not effective whatever algorithm you use.


GLBP works by having the AVG to answers ARP requests for the GLBP VIP.

Once your switch C3750 has resolved the VIP address it will use that MAC address for 4 hours. (default ARP timeout)

So round robin can provide use of both routers over a big time scale but this is not considered a form of load balancing.

Unless relying on proxy-arp on edge routers interfaces and  with C3750 having a default route with only the outgoing interface, but this is not recommended as would cause a lot of ARP activity and also could lead to high cpu and/or high  memory usage


If your C3750 license allows to use a dynamic routing protocol you can get a better load balancing by having  the two edge routers to advertise a default route and the C3750 can install both routes.

The use of a dynamic routing protocol would allow to advertise a default route in OSPF for example only when a BGP default route is received from the provider on each edge router.

If a link or an eBGP session fails the edge router can remove its own default route from OSPF and the C3750 will learn this and will use only  the other one.

with ospf is enough to use a config like

edge router

router ospf 10

default-information originate type 1

network 10.10.10.0 0.0.0.255 area 0



switch 3750:

router ospf 10

network 10.10.10.0 0.0.0.255 area 0

!+ other network ... area statements for client vlans

network 10.10.20.0 0.0.0.255 area 0

....

network 10.10.50.0 0.0.0.255 area 0



let's suppose network between edge routers and internal switch is 10.10.10.0/24 )(just an example)


Even using two default static routes with next-hops the edge routers would be more effective for load balancing but it would lead to problems in case of failure of one edge router.

In this case using two HSRP groups in the so called MHSRP solution in the same vlan to provide two different VIP IP addresses to be used as next-hops in two default static routes on C3750 can be an acceptable solution.


GLBP would work well if the client vlans were directly connected to the edge routers so that multiple clients per vlan exist and load balancing using round robin would be effective.


Hope to help

Giuseppe

mrsystemengineer Sat, 02/13/2010 - 06:55
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Dear Gulsair,


         I dont have any ospf configuration on router and switch.  Just i have default route on cisco routers (ISP1 and ISP2) and just vlans on core switche.


so what i have to do for load balancing.


regards,

Ganesh Hariharan Sat, 02/13/2010 - 07:55
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Dear Gulsair,


        I dont have any ospf configuration on router and switch.  Just i have default route on cisco routers (ISP1 and ISP2) and just vlans on core switche.


so what i have to do for load balancing.


regards,

Hi,


what i understand with your setup will be like this


                                   R1 ----

                                                  Switch

                                   R2 ----


to achive loadbalaning for client from inside to outside network you can either use EIGRP or OSPF as suggested by Giuslar.If you have all are cisco device then you can configure EIGRP between R1,R2 and Switch automatically equal cost load balancing will be done by EIGRP.


Check out the below link to configure EIGRP


http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfeigrp.html


Hope to help


Ganesh.H

Giuseppe Larosa Sat, 02/13/2010 - 12:15
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Hello,

I've already provided a sample configuration for OSPF in my previous post.


Ganesh has provided a link for EIGRP.


The key point for moving to a dynamic routing protocol is to check that your C3750 supports it at least in a limited form like EIGRP stub router.


post

sh ver

of your C3750


sh sdm prefer



Hope to help

Giuseppe

mrsystemengineer Sat, 02/13/2010 - 12:23
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Dear Guilsar,



see the below my 3750 switch version:

version 12.2

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption




can you send me the link to configure ospf on switch side or router side.  I have some doubts about configuration of OSPF on switches or routers.


already i have configure glbp on routers and default to route on switch.


can you send me link plz or details configuration examples.


waiting for reply.


regards,

Giuseppe Larosa Sun, 02/14/2010 - 02:40
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Hello Mrsystemengineer,


I see you have ip routing  enabled on your switch


From

sh ver

sh sdm prefer


it would have been possible to say if OSPF is supported or not.

However, this can be easily checked with an attempt:


config t

router ospf 10


if the command is accepted you can use OSPF on your router.


See the following  OSPF design guide


http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml


Hope to help

Giuseppe

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