DSL load Balancing

[tkatsiaounis]

     Hello.

I have a Cisco 2811 router with two HWIC-ADSL cards configured for dsl connection. I have two lines from the same ISP and i am load balancing between them. I have created a couple of SLA's to check the state of the connections and add to the routing table the two default routes if both are up or any one of them is up.

My problem is that when i  try to download big files (especially antivirus updates) the download at some point stops (especially the antivirus exits with an error of unreachability). If i shut down one line everything works fine.

Could i use something (configuration-wise) to prevent this problem from happening?????Is there any way i can combine the two lines???? They are simple ADSL connctions with static ip's.

Thanks a lot in advance.

[lgijssel]

The problem you describe is most likely caused by out-of-sequence traffic. The basic solution is to  make sure that you have per-session load balancing.

This means all traffic for a session (i.e. a download) is sent over one link. Also, this should be the same link in both directions.

Your nat solution is also relevant. Do you utilize one nat address per interface or is the nat-outside address the same on both links?

In the latter case, your ISP setup can also make a difference because you typically get out-of-sequence traffic by load-balancing in a round-robin fashion (i.e. per packet) over multiple links. As you ISP is also performing load balancing, you need to know how he does this. Per-packet or per-session?

To really help you we need more detailed info about your nat setup. Thank you.

regards,

Leo

[tkatsiaounis]

My nat configuration is the following. The lines are purchased seperately they are not combined by the ISP.

ip nat inside source route-map Route1 interface Dialer0 overload
ip nat inside source route-map Route2 interface Dialer1 overload
!

!

access-list 110 permit ip any any
!
!
!
!
route-map Route1 permit 10
match ip address 110
match interface Dialer0
!
route-map route2 permit 10
match ip address 110
match interface Dialer1

[lgijssel]

How about CEF? Is it enabled or disabled?

Try to adjust the acl so that it matches one ip for link A and another for link B.

regards,

Leo

[tkatsiaounis]

CEF is enabled.

The thing is that behind the router there is a software firewall/router which NAT's all internal lan's to an ip and then forwards traffic to the router. I have seen somewhere i should enable cef load sharing port algorithm but it did not help.

[lgijssel]

Perhaps you can try to split the natting on the fw so that you get two ip sources towards the router?

When this works, CEF will be able to ensure per-session load balancing.

[tstamatopoulos]

can you please give us a

sh ip cef 0.0.0.0

command output?

[tkatsiaounis]

sh ip cef 0.0.0.0
0.0.0.0/32
  receive

[tstamatopoulos]

sorry, misstyped,

sh ip cef 0.0.0.0 0.0.0.0

and

sh ip route

also