One of the ways I did load balance before for one of my client was this.
Set HSRP on both of the router. (so 2 sets of HSRP)
Each one of them is Active HSRP router and Standby for the other.
So, ie) Router A: 192.168.0.10 Virtual 192.168.0.11 Actual (Active)
192.168.0.20 Virtual 192.168.0.21 Actual (Standby)
Router B: 192.168.0.10 Virtual 192.168.0.12 Actual (Standby)
192.168.0.20 Virtual 192.168.0.22 Actual (Active)
Depending on your size of network and how it is subnetted, point half of
your clients to one router and the other half to the second router.
In this case, it is load-balancing (sort of, not really) and also
falut-tolerance.
There are other ways to do it as well, but if it is DSL and if it is small
network (less than 50 ~ 100 nodes), I recommend this one.
Thanx.
Edward B. Kim
CCNP, CCNA, CCDA, A+, MCSE, CNA
-----Original Message-----
From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 06, 2001 11:36 PM
To: [EMAIL PROTECTED]
Subject: Re: Cisco 1720, DSL and OSPF
>I have a customer who, at present, has 2 dsl line going out to 2 seperate
>ISP's through Alcatel Modems.
>What he would like is to be able to load balance with route-redundancy over
>both lines. I figure the 1720 with 2 adsl modules can take care of his
>router but I am not sure what routing protocol they need to implement so
>they get true equal-cost load balancing. Is OSPF the solution or can RIP do
>this?
>Any info truly appreciated.
>
>P.
>
Again, routing protocols don't load balance. The route selection
process decides on load balancing, as long as it has more than one
eligible route to the destination. Such routes can even be static.
With a few caveats, every IP routing protocol can produce multiple
equal-cost routes (caveats include that OSPF will not generate
parallel externals, and standard BGP doesn't have a concept of equal
cost load balancing).
Equal cost load balancing has its greatest applicability in an
enterprise, or with multiple links to the same ISP. Unless your
customer has a thorough understanding of global routing, he is likely
to get a rude awakening if, for example, he sets up both external
links as defaults, each to a different ISP. I would suspect that
30-40% of the queries he sends out one path will return on the other
path.
You can get a certain amount of load sharing, not load balancing,
with BGP, but complex issues remain. With BGP _and_ appropriate
agreements with both carriers, you can get a fair amount of load
sharing of enterprise-to-ISP traffic. It is far more difficult to
get load sharing in the other direction.
My gut tells me that this customer is too small to achieve any useful
degree of multi-ISP load sharing, and indeed multihoming. You haven't
even touched the addressing and DNS issues involved. A much more
reasonable approach might be to contract for single-provider
multihoming (i.e., links to two different POPs).
From my own experience, however, the DSL facility itself is likely to
be the source of the greatest number of problems. It's unlikely that
the two DSL links will have any level of diversity.
Let's put it this way -- I am considering attempting to get some
level of multihoming for improved availability out of my home office,
and I have a thorough knowledge of exterior routing. My more modest
approach would be to back up the DSL connections with multiple PPP
dialups, accepting the speed loss. If I can get cable connectivity,
that would help for some applications, but still has nasty addressing
problems. An alternative might be to get a frame relay over T1
connection to the provider, and back it up with SDSL. I'm far too
small an installation to get globally routable address space, but I
can cobble up something to give diversity for specific applications
(e.g., extranet VPN access).
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