Direct Standby Notes

• In a typical redundant router configuration, the INSIDE port on the LEM should be connected to the switch or router on the parallel path so that the PacketShaper can be accessed remotely. However, in a topology in which there are two routers on each side of each PacketShaper, you should NOT make this connection because you would not be able to access the unit remotely. If a network component fails in this type of topology, you will need to provide a secondary route to the unit.
  
  
• In order for the direct standby feature to work, both PacketShapers must have identical touch passwords. If you change the password on one of the units when direct standby is enabled, direct standby will continue functioning, giving you an opportunity to change the password on the other unit. However, if one of the units is reset while the two units have different passwords, direct standby will be disabled until the passwords are identical and both units are reset (or until standby is turned off and then back on).
  
  
• When two PacketShapers are directly connected, traffic is running, and then the direct standby feature is disabled on one of the partner units, the copied packets coming through the direct link between the units could leak onto the LAN causing the receiving unit to see duplicate packets. Note that this situation happens only for a short time period because the unit sending the copied packets would stop sending packets immediately upon realizing that its partner is down.
  
  
• Be aware that outages of components in a redundant topology could cause discovery of new paths and routes. If this occurs while you have an existing Telnet or browser session with either PacketShaper, the session will be terminated. After the paths and routes have stabilized, you will have to start a new session.
  
  A similar loss of connectivity could occur right after direct standby is enabled or disabled. This loss of connectivity is transient and recoverable after the new paths and routes have been established.
  
  
• When using the direct standby feature in a load-sharing topology, set the link speed to the sum of both WAN links. Because each unit receives copied packets from its partner, the overall Inbound and Outbound partition sizes must be able to support that level of extra traffic. In this situation, you may want to use the access-link monitoring feature (advanced mode) to monitor the routers’ WAN interfaces and avoid over-subscribing the WAN bandwidth.
  
  
• The direct standby feature assumes that broadcast and multicast packets are automatically seen by both units, so these packets are not copied to the partner unit. As a result, the two units will have a difference in the value of the non-compressible-bytes variable when using Xpress in direct standby mode. In addition to broadcast and multicast packets, PacketShaper does not copy attack packets and IPComp control packets.

PacketGuide™ for PacketWise® 7.5