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Chapter 12
Value Added Services (VAS) Traffic Forwarding
Disabling a VAS Server
A VAS server can be disabled for maintenance via the CLI.
No errors are reported on a disabled VAS server. However, if disabling the server reduces the number of
active servers to below the minimum number configured for the group, it will bring down the VAS Server
Group since a disabled VAS server is equal to a VAS server in a Down state.
Health check is not performed on disabled VAS servers.
VAS Status and VAS Health Check
To manage the VAS redundancy, the SCE platform needs to know the state of each VAS server. The SCE
platform performs periodic health checks for all the configured VAS servers. These checks are the basis
for VAS redundancy control; they enable the SCE platform to identify and react to VAS server failure,
and to check the connectivity of the SCE platform-VAS server before enabling the server to handle
traffic.
The health check is performed over the VAS link, the link that connects the SCE platform with the VAS
servers. It validates the traffic flow between the SCE platform and the VAS server in both directions
through special health check packets generated by the SCE platform.
The health check mechanism does not require special interaction with the VAS device, since the VAS
server does not need to answer the health check packets, only to pass them as they are back to the SCE
platform. As long as the packets are received by the SCE platform, the VAS server is considered to be
alive. Failing to receive the packets back from the VAS server within a pre-defined time window is
considered by the SCE platform as a failure of the VAS server and the server status is changed to Down.
Important information about the health check packets:
•
•
The SCE platform uses default UDP ports between 63140 and 63155, unless the user has configured
different ports for the health check.
The SCE platform adds its own layer 7 data on top of the UDP transport layer. This data is used by the
SCE platform to validate the correctness of the packet upon retrieval.
The health check is performed under the following conditions:
•
•
•
•
•
If the check is enabled, but any one of the conditions is not met, the server state will be Down (the same
as if the server did not pass the health check).
To check the connectivity with the VAS server before enabling it to handle traffic, the server should not
be assigned to any group.
OL-7827-12
They are carried over UDP flows
Their source and destination IP addresses are configurable by the user
IP addresses should be:
Unique to the SCE platform
–
Addresses that will not be used by the network traffic (such as private IPs)
–
VAS mode is enabled
VAS server is enabled
Health Check for the VAS server is enabled
Server has VLAN tag
Pseudo IPs are configured for the GBE interfaces
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
VAS Status and VAS Health Check
12-11
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