Traffic Load Sharing

rameezsardar · ‎12-12-2008

Hi,

I have two gateway routers that are connected with L3 switches. R1 with SW1 and R2 with SW2

R1 R3

SW1------SW2

R1 f0/0 10.1.1.1

R2 f0/0 10.1.1.2

SW1 vlan10 10.1.1.3

SW2 vlan10 10.1.1.4

R1 and R2 are connected with provider via bgp and connected with switches via EIGRP. Switches interfaces that are connected with Routers are in same vlan 10. R1 and R2 are advertising default route with same cost so both switches have default route with two equal cost next hop. Switches are running HSRP for internal users.

Now traffic coming from inside network is for same destination (that is a proxy server on internet). And the problem is, HSRP active switch send all traffic to one Router and not loadbalancing on both routes (may be because destination is same). My requirement is even traffic is for same destination, it should be loadbalance between both links.

Waiting for solution

Best Regards

Giuseppe Larosa · ‎12-12-2008

Hello Rameez,

I would take a different approach:

on client Vlans I would use GLBP instead of HSRP so that both switches will be used for outgoing traffic this should provide a chance to have both routers used.

Check also the sh ip route of the proxy destination because it is not the default route but the route to the proxy to be used: both R1 and R2 have to advertise proxy ip subnet (a DMZ I suppose) with same parameters.

To do as I suggest the first step is to verify if GLBP is supported what model are Sw1 and Sw2 ?

otherwise you should try to implement per-packet load-balancing but again I'm not sure your switches support it

Hope to help

Giuseppe

Joseph W. Doherty · ‎12-12-2008

"(may be because destination is same)."

According to http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a0080094806.shtml#backinfo, CEF should route source/destination pairs across different paths, unlike earlier destination only caching. Is CEF running on SW1 and SW2?

PS:

Concerning Giuseppe's of using per-packet load balancing, be aware of issues that can arise when packets of the same flow are resequenced.

viyuan700 · ‎12-12-2008

I dont know which one is better HSRP or GLBP as far as laod sharing is concerned.

"And the problem is, HSRP active switch send all traffic to one Router and not loadbalancing on both routes (may be because destination is same). My requirement is even traffic is for same destination, it should be loadbalance between both links"

If you just want that your standby router also is active for some user then load sharing is also possible in HSRP. You have to define one more standby ip for which standby router has higher priority then active router.

rameezsardar · ‎12-16-2008

Hi,

My requirement is that active switch should forward traffic to both routers and loadbalance. I cann't change HSRP with GLBP or HSRP multiple group because of some limitations. One solution could be possible that i can configure on switches per-packet loadsharing using interface level command but i need your suggestion is it a right way in my scenario?

Any if someone have experience this problem and use this per-packet loadsharing please add your comments how efficient is it?

Regards

viyuan700 · ‎12-17-2008

"R1 with SW1 and R2 with SW2"

and

"R1 and R2 are advertising default route with same cost so both switches have default route with two equal cost next hop"

Your above staements say different things first Sw1 connected to R1 and Sw2 connected to R2 and later "both switches have default route with two equal cost next hop" means is Sw1 connected to R1 and R2 both.

If Sw1 only connecetd to R1 then load sharing is not possible.

If it is connecetd to R1 and R2 both with equal cost then it needs further analysis why it is not doing so?

Giuseppe Larosa · ‎12-17-2008

Hello Rameez,

if all traffic from internal to internet has destination address = proxy-ip you need to verify the

sh ip route proxy-ip on the active switch:

you can have two equal cost default routes but if you are not using them for reaching the proxy ip address load balancing doesn't happen

As noted by Joseph even if the destination is only one load balancing should still happen but the first requirement is two equal cost paths to the proxy address from the point of view of internal switches.

Hope to help

Giuseppe