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Configure GLBP on 1800

Hello to all,

We have 2 1800 model routers. One is used in the production network and other is spare.

We want to test GLBP with these routers. We also do not want to disturb the existing config in the router.

What i want to know is - can i configure the router with glbp and test it without effecting the current config ?

The production router config is quite simple. It has one primary and 2 secondary ip configured on its fa 0/0 and other fa 0/1 with ISP conn..

If i configure the spare router with any virtual IP and also the production router with the same virtual IP, will it effect the existing users ?

Please guide. Thanks in adv.



Re: Configure GLBP on 1800

Do not use production routers to test new technologies. Configuring GLBP will affect current network traffic.

Super Bronze

Re: Configure GLBP on 1800

If your production router has an unused Ethernet interface, then you would be in a good position for testing GLBP on it with minimal possible impact to your production network. Otherwise, you might be able to define a GLBP address on an active production interface. (The reason I say might, I'm not 100% certain what impact the existing secondary addresses might have. There shouldn't be any issue with a GLBP address and "normal" ip address sharing the interface.)

What you do want to avoid, for a test, is using one of your existing production gateway addresses. I.e. it's fine to share a "new" virtual address between two routers (assuming it doesn't conflict with any other device), but if you reassign an existing gateway address, you can easily impact active users.


Collin's post, to avoid tests on production systems, is good advice, but if your really suffer from lack of equipment, it might be doable. If you do end up testing on production equipment, next best situation (rather than having dedicated test equipment) is to attempt to limit your changes/tests to non-peak times.


Just tried this on a 2801:

Router#sh run in fa 0/1

Building configuration...

Current configuration : 203 bytes


interface FastEthernet0/1

ip address secondary

ip address secondary

ip address

duplex auto

speed auto

glbp 1 ip


So, it appears you might be able to test GLBP on a production interface.

Community Member

Re: Configure GLBP on 1800


Thanks all for receptive replies.

Certainly, testing on production router is not my first choice and so i wanted to confirm if it would effect any of the current users.

I have 2 interfaces, but both are used.

I will be using, one of the interface and give it a new virtual ip as gateway with the spare router.

I wanted to further confirm that, if the interface already have a primary IP and 2 secondary IPs in use, and i create a virutal IP for glbp, the users would still be able to use the primary and 2 seconday IPs on the router ? I mean sort of, glbp virutal ip would not take precendence as the default ip for all routes etc...

Please guide. Thanks in adv.

Super Bronze

Re: Configure GLBP on 1800

As long as your other hosts are using an existing explicit gateway address, the GLBP test address, I believe, should not be an issue. For testing, you'll have to set those hosts that want to use the GLBP virtual address as their gateway's address. If, on the other hand, you get to the gateway address using proxy, I suspect, but I'am uncertain, the router might return the GLBP address. (Reason I'm uncertain about proxy gateway, when using HSRP/GLBP/VRRP have always used explict host gateway addresses.)

Community Member

Re: Configure GLBP on 1800


Thanks for reply. It was very helpful.

I would test and see.

Thanks again.

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