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New Member

GLBP load balancing and ospf routing problem - not load balancing

Hi,

Please review my attached .jpg for a more detailed explanation.

I am trying to set up GLBP to load balance 2 routers, 1 serial link (GLBP weight 100) and 1 isdn link( GLBP weight 90) connected to the same router via differnent mediums.

I am using ospf as a routing protocol and using the command load-balancing weighted for glbp.

Basically I see no traffic going over the isdn link when i transfer data.

The glbp section works well when i fail the serial router but the load balancing does not. I would have expected at least a percentage of the traffic to use the isdn link especially seeing as I have throttled the serial to 64k and am transferring large files. I am eventually wanting to utilise all available bandwidth

Is this a problem with opsf selecting only one route out and do I have to even the costs of each link somehow ?

any ideas appreciated,

cheers

Richard

5 REPLIES

Re: GLBP load balancing and ospf routing problem - not load bala

Hi Richard,

I am assuming you have only one OSPF entry in your routing table. And I also assume, that the serial is considered to be a T1 by OSPF as this is the default bandwith. please do a show interface and have a look at the bandwidth displayed. In case you wnt to load balance with OSPF you need to have both pathes with the same metric, f.e.

interface Serial0

bandwidth 64

Be aware that in case you use CEF this will also impact load balancing. CEF per default does load sharing per session. So make sure to have a couple of sessions to see the effect.

Regards

Martin

New Member

Re: GLBP load balancing and ospf routing problem - not load bala

Thanks for that reply.

I have checked and I have set both the serial router to run at only 64k and the isdn router to run at only 64k. They are however not load balancing.

When I pass data the serial takes all the load until I fail this route at which point the isdn takes over.

I have noticed in sh ip ro that the costs associated with eac link vary slightly so am wondering how do I manually set up each cost to be that same and allow the weighting of the routers (GLBP) to deal with with router to use ?

Also, is this a safe and recomended way to run GLBP ?

Please advise,

Richard

New Member

Re: GLBP load balancing and ospf routing problem - not load bala

You can manually change ospf cost of outgoing interfaces by using 'ip ospf cost' command.

http://www.cisco.com/en/US/products/ps6350/products_command_reference_chapter09186a0080446b1b.html#wp1091126

Thanks,

Praful

New Member

Re: GLBP load balancing and ospf routing problem - not load bala

Thanks to everyone for their suggestions so far but I am still having problems, my configs are below :

Router A - Back-2-Back Serial running at 128k

GLBP Priority - 100 (default)

intf0/0 :

glbp 1 ip 1.1.1.1

glbp 1 preempt delay min 20

glbp 1 weighting 100 lower 91 upper 99

glbp 1 load-balancing weighted

glbp 1 weigthing track 1 decrement 10

glbp 1 weigthing track 2 decrement 10

glbp 1 forwarder preempt delay min 20

Router B - ISDN2e 128k

glbp 1 ip 1.1.1.1

glbp 1 priority 90

glbp 1 weighting 100 lower 91 upper 99

glbp 1 load-balancing weighted

glbp 1 weigthing track 1 decrement 10

glbp 1 weigthing track 2 decrement 10

I have also set the s0/0 and the bri0/0 interface to the same ospf cost using "ip ospf cost 1600".

The problem I am having is that they simply wont load balance a large file. Only 1 interface sends the data at a time. Any thoughts ????

I would like to take advantage of the full 256k available.

Also, the router b when dialled up always seems to take control of passing data even if I give the router a serial a larger bandwidth and higher priority. I thought the priority command should have sorted this ?

Any ideas appreciated,

Richard

New Member

Re: GLBP load balancing and ospf routing problem - not load bala

Hi,

I have used a syslog tool to confirmthe states of the f0/0 ports during normal transactions.

When both routers are active the states are set to active ( for the lead router ) and Listen for the backup router, i.e. waiting for the lead router to fail.

I have noticed however that the port states are set to active for one port on one router and listen on the secondary router port.

If I am looking to load balance over both links should both these ports not say active and therefore share the load ?

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