Alteon Application Switch Operating System Application Guide
WAN Link Load Balancing
Document ID: RDWR-ALOS-V2900_AG1302
655
Health Checking and Multi-homing
When using health checking with WAN link load balancing, sometimes disruption of service on one
link may not be immediately apparent. This is because of how health checking interacts with a load
balanced WAN environment.
Consider an Alteon that is multi-homed to two service providers. Alteon has WAN link load balancing
configured for incoming and outgoing traffic. If the link to the first service provider is removed, the
health check for this link does not fail even though the corresponding interface is down. This is
because the health check packet is still being sent and received through the connection to the
second service provider. This is a by-product of the tendency of any routing protocol to re-route a
packet to an active link.
To overcome this problem, two filters can be used to on the two load-balanced ports to suppress the
ICMP echo reply which makes the health check fail if the link fails.
Example
This example applies filter 10 to the link to the first service provider:
After the filter is applied to the first link, the filter on the second link is applied. The following
commands would apply filter 20 to the link to the second service provider:
Note:
In addition to the application of the filters, Radware also recommends using a static route.
>> /c/slb/filt 10
ena
action deny
sip 80.1.1.1
smask 255.255.255.255
dip 50.1.1.2
dmask 255.255.255.255
proto icmp
vlan any
/c/slb/filt 10/adv
icmp echorep
/c/slb/filt 20
ena
action deny
sip 50.1.1.1
smask 255.255.255.255
dip 80.1.1.2
dmask 255.255.255.255
proto icmp
vlan any
/c/slb/filt 20/adv
icmp echorep