Citrix NetScaler EE, Руководство по установке и настройке

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How Group Mode Works
Dec 06, 2012
In group mode, the appliances that are part of the group each take ownership for a portion of the group's connections. If
a given appliance is the owner of a connection, it makes all the acceleration decisions about that connection and is
responsible for compression, flow control, packet retransmission, and so on.
If an appliance receives a packet for a connection for which it is not the owner, it forwards the packet to the appliance
that is the owner. The owner examines the packet, makes the appropriate acceleration decisions, and forwards any output
packets back to the non-owning appliance. This process preserves the link selection made by the router, while allowing all
packets in the connection to be managed by the owning appliance. For the routers, the introduction of the appliances has
no consequences. The routers do not need to be reconfigured in any way, and the appliances do not need to understand
the routing mechanism. They simply accept the routers' forwarding decisions.
Figure 1. Sending-side Traffic in Group Mode
Figure 2. Receiving-side traffic flow in group mode
Group mode has two, user-selectable failure modes, which control how the group members interact with each other if one
of them fails. The failure mode also determines whether the failed appliance's bypass card opens (blocking traffic through
the appliance) or remains closed (allowing traffic to pass through). The failure modes are:
Cont inue t o accelerat e- Cont inue t o accelerat e- If a group member fails, its bypass card is opened and no traffic passes through the failed
appliance. The result is presumably a fail-over if redundant links are used. Otherwise, the link is simply inaccessible. The other
appliances in the group continue to accelerate. The usual hashing algorithm handles the changed conditions. (That is, the
old hashing algorithm is used, and if the failed unit is indicated as the owner, a hashing algorithm based on the new, smaller
group is applied. This preserves as many older connections as possible.)
Do not accelerat e- Do not accelerat e- If a group member fails, its bypass card closes, allowing traffic to pass through without acceleration.
Because an unaccelerated path introduces asymmetric routing, the other members of the group also go into pass-through
mode when they detect the failure.