How to load balance our installation internet installation

[johnny99]

Hi

I have been thinking a little about how best to load balance our internet installation, and I hope someone has some hints I can use.

We use BGP4 and HSRP

We have 2 ISP's and to each we have 2 indepentend connections.
Basicly I want to use as simple a BGP4 setup as I can, but if possible I would like to balance between the two connections to a given ISP that BGP4 sees as having the shortest path.

ISP1 is an international strong carrier (2 x 100 Mbit/s)
ISP2 is a domestic strong carrier (2 x 10 Mbit/s)

We don't have a load problem at all, but I would just like to use both connections to each ISP to minimize loss of access when on of the connections goes down (I know we talk short loss before BGP4 has changed the routing)

Router and connection setup is something like this:


Internet


! ! ! !
ISP1 ! ! ISP2 ISP2 ! ! ISP1
! ! ! !
!-----------! !-----------!
! 7206 ! ! 7206 !
!-----------! !-----------!
! !
! !
------------------------------
Inside

/johnny

 

[KiscoKid]

Hi there.

I think so long as you load-balance your LAN clients across both 7206's, you'll get the load-balancing you want across each ISP's connection.

For instance, if LAN client A uses 7206(1) and LAN client B uses 7206(2) outbound, LAN client A will use either of the 2 ISP connections coming into 7206(1) and similarly LAN client B will use one of 2 connections on 7206(2).

If, for example, the route to a particular destination is preferred via ISP 1 and both LAN clients access this same remote destination, then load-balancing is achieved across both connections from the same ISP.

You can achieve effective load-balancing between the routers using either MHSRP or GLBP (assuming no LAN protocols have been deployed) for a statically-routed LAN.

Once a LAN client's packet hits a particular router, there are a number of factors that can influence the best path to a remote destination. You may find that some of load-balancing could well be achieved without having to do anything. If you're a little lucky, you may find the domestic carrier has a better AS Path to domestic websites whereas the international carrier (probably a Tier 1 provider) will likely be the preferred option to international sites.

It's unlikely you'll get a nice 50/50 split between the ISP's but you should be able to achieve a nice even split between both connections to a particular ISP (if you deploy MHSRP or GLBP).

If you want to control which ISP your traffic goes, there are numerous ways of influencing this. A popular way is to only accept routes from say networks 1.x.x.x up to 128.x.x.x from ISP A and accept anything from 129.x.x.x and upwards from ISP B. This achieves some kind of load-balancing.

If you need config help with configuring ISP load-balancing, let me know and I can assist with it. However you may be lucky and it would well load-balance anyway as it's unlikely thay the international carrier will be preferred for ALL routes but that behaviour can be changed if required.


This is turning into a long post but all the above only really related to outbound load-balancing. If you are also interested in controlling inbound load-balancing from each ISP, you can influence this again by a few methods. Popular ways of doing this is by prepending AS paths to outbound advertisements and/or manipulating the route metrics. AS pre-pending is arguably more popular as ISP's don't have to and don't always obey BGP route metrics.

This is a really big post - apologies for this. By the way if you need further clarification on some of this, have a look at some of the following links:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf3

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_white_paper09186a00801541c8.shtml