glbp question

Unanswered Question
Dec 9th, 2007

scenario:

2 diff isps

2 internet routers

2 diff ip address space (1 from each isp)


is there anyway we can trick GLBP to load balance the traffic going out in here..say internet connectivity.


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paul.matthews Mon, 12/10/2007 - 04:57

No. The problem is that you don't have your own address space, so when traffic changes the link it goes out of the address it uses will change, which will rather confuse matters.

paul.matthews Mon, 12/10/2007 - 07:28

Do *both* ISPs give you the same block? Will they carry the routing for the block from the other ISP?


To handle load balancing, you need *one* IP block that you can route vis both (this also means you will probably need to run BGP as well).


If you have something like:


ISPl - Address block 1 - you - address block 2 - ISP 2


then you will be using different addresses for traffic going to the different ISP.


You may be able to use policy based routing to do something like route web traffic one way and other traffic the other, to make sure a single connection always went the same way, or a CSS "backwards" to spread http traffic such that connections to the same places go the same way, but if you want to really load balance, you need to just use one address blobk both ways.

cfajardo1_2 Tue, 12/11/2007 - 00:16

So if i only have block of ip addresses from say ISP1, doing a GLBP means i have to use same block for the router connecting to ISP2.

paul.matthews Tue, 12/11/2007 - 01:46

The simple answer is yes, but we are getting into complex situations here.


To use GLBP to load balance your connectivity out to the internet you need to be using one address blok, and that needs to be routed via both ISPs. ISP2 may not let you advertise a block of addresses from ISP1.


You also need to look at your connectivity. If you are using NAT, you need to look at using a single logical device to handle the NAT - that can be a resilient pair of firewalls for example, that talk to each other and keep each other aware of NAT translations so that a packet hitting either firewall on the return path will be understood.

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