GLBP with single client

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I have 2 1721 routers which I have configured for glbp, i have configured loadbalancing as round-robin, however im not sure its going to work.

My upstream layer 3 switch is doing the routing to the routers and as such, the switch is going to be the only device connecting to the glbp address.

I believe that glbp round robin sends each request to a different mac address hence the sharing of load. But if its only getting 1 request for that address from the switch, am I right in thinking that its only ever going to load balance me to a single router?

Is there a way to get around this and load balance connections from a single host connection?


J Fisher

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Giuseppe Larosa Fri, 10/24/2008 - 10:53
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Hello J,

in this case GLBP cannot load balance: once that the switch has made an ARP request for the default gateway game over.

You should consider:

using two default static routes pointing to the routers LAN ip addresses the switch will load balance or better use a dynamic routing protocol like EIGRP or OSPF.

GLBP and HSRP are to be used for end user devices like PCs a L3 switch can take part in your routing infrastructure

Hope to help


Jon Marshall Fri, 10/24/2008 - 12:54
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Just to add to Giuseppe's post. As he says GLBP/HSRP etc. are used for gateway redundancy for end devices such as servers/clients etc.

Routers, L3 switches do not normally use GLBP/HSRP virtual addresses, they use the real IP addresses attached to the interfaces.

So when you say

"Is there a way to get around this and load balance connections from a single host connection?"

this is misleading if i understand correctly. The L3 switch is not a single host connection it is just another router to all intents and purposes.


Thanks guys for the response.

yes sorry i wrote the question in a hurry and its a little misleading..

my switch is the gateway for the hosts on that part of the network, the switches route of last resort is the routers glbp address.

We have tried using 2 static routes on the switch, creating 2 hsrp groups for redundancy and to allow 2 primarys, but had problems with dropped connections.

we have 2 routers on this site with 4 serial connections to 2 routers on another site.

the routers are using eigrp and the switch the other end is also cisco and we are sucessfully using eigrp on that, but the switch in question here is not cisco.

So our options are limited to ospf to provide the loadbalancing or static routes (which as above hasn't worked for us), which I was hoping to avoid. But if its the only way forward then I shall explore that option.

Many Thanks for your advice so far.

J Fisher

Joseph W. Doherty Fri, 10/24/2008 - 14:45
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Two methods come to mind. If you're using a dynamic routing protocol with the far side, loss of the peer should stop using that path. Assuming there's also dynamic routing within the site, traffic should be redirected to other router with good path.

If you're using statics, some of the later IOSs support usage of SLA to monitor path and repoint static route. This is an enhanced version of the interface "track" command.


For reference to the latter, see Jon's post in:


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