14-8
Cisco SCE 8000 10GBE Software Configuration Guide
OL-30621-02
Chapter 14 Value-Added Services (VAS) Traffic Forwarding
How VAS Traffic Forwarding Works
5.
The packet is sent to the VAS subscriber port from Cisco SCE platform Port 4 (N).
6.
The VAS server processes the packets and either drops the packet or sends it back to the Cisco SCE
platform from the VAS network port to the Cisco SCE platform subscribers Port 3 (S).
The VAS server passes the VLAN tag transparently. This is important to enable the Ethernet switch
(not shown) to route the packet back to the proper Cisco SCE platform.
7.
The Cisco SCE platform receives the packet on Port 3 (S), drops the VLAN tag, and passes the
packet towards the network through Port 2 (N).
Note
To use VAS, at least four interfaces should be active on the Cisco SCE device.
Load Balancing
VAS servers can be grouped logically according to their service type. Consider, for example, a system
that requires both FTP caching and virus filtering. A single VAS server for each service might not have
enough capacity. For example, assume that the system requires five VAS servers, three to provide FTP
caching, and two to provide virus filtering. Defining two VAS server groups, for example, FTP caching
and virus filtering, permits load sharing across the servers for each server group.
The subscriber package determines the VAS server group to which the flow should be attached. The
selection of a specific VAS server from the VAS servers within the group is based on the current load on
each VAS server. The system tries to create an equal subscriber load for all the VAS servers belonging
to the same group.
In some cases, a single VAS server may be used by more than one Cisco SCE platform. Remember that
the Cisco SCE platform performs load balancing only on the traffic that it sends to the VAS server; it
receives no information regarding the load the VAS server may be bearing from a different Cisco SCE
platform. It is vital to properly allocate available VAS servers to the Cisco SCE platforms to ensure a
balanced load on each VAS server.
Load Balancing and Subscribers
The system balances the usage of the VAS servers within a VAS server group, trying to create an equal
subscriber load for all the VAS servers in one VAS server group. The load balancing is subscriber based,
that is, the subscribers are evenly distributed between the servers.
VAS load sharing is subscriber based rather than bandwidth based to ensure that all the traffic of the
subscriber gets to the same server so that the server can make subscriber-based decisions.
The Cisco SCE platform uses the same VAS server for all the traffic of a subscriber (per server group)
even if there is a change in the number of active servers in the group. Traffic from a subscriber is assigned
to a new server only if the current server becomes inactive. This applies only on new flows. Flows that
were already mapped to a server before it became active remain attached to it.
The mapping of subscriber to VAS servers is not saved across subscriber logouts or Cisco SCE platform
reload.
