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How VAS Traffic Forwarding Works
Requirements for VAS Servers
Since the VAS devices are installed behind the SCE platform, they should follow the network behavior
of the SCE platform.
The two main guidelines that VAS device should follow are:
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Layer-2 Transparency
Note the following guidelines for handling VAS services non-management traffic:
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VAS Management Traffic
VAS devices that are managed inband (through the traffic interface), must meet the following
requirements
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Cisco SCE 2000 and SCE 1000 Software Configuration Guide
12-4
They should be equipped with two separate interfaces – subscriber side and network side.
Traffic toward the subscribers should be sent from the subscriber interface and for the Internet from
the network interface.
Transparency in layer-2 – This means that the VAS servers act like layer-2 switches from the
networking perspective. They are not allowed to change anything in the traffic headers or to generate
new traffic on behalf of themselves
The VAS services should work in promiscuous-mode in layer-2 and accept packets with any
destination MAC address.
When forwarding traffic back to the network after processing (injecting), the VAS devices must
preserve the original layer-2 headers containing the MAC addresses and the VLAN tag. The VAS
devices may not change the MAC addresses (destination or source) or the VLAN tags.
New traffic can be injected in the context of existing flow only.
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The VAS device is not permitted to initiate new flows.
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When injecting traffic, the layer-2 information (MAC addresses, VLAN tags, and the IP / TCP
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parameters) must be taken from the context of the flow into which the traffic is being injected.
VAS devices may not generate any network transactions on behalf of themselves or replay such
transactions. Network transactions such as ARP requests or pings are not permitted.
Management traffic should either be carried over a dedicated VLAN or without any VLAN header.
The switches that are connected to the VAS devices should be directly connected to the POP router.
The switches that are connected to the VAS devices should be configured so management traffic will
be sent directly to the router and not through the SCE platform.
Chapter 12
Value Added Services (VAS) Traffic Forwarding
OL-7827-12
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