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  1. What does Load balancing Hash mean in CEF?
  2. Which commands are use to configure?
  3. Is it support to other vendors except Cisco?
  4. If it is not support other vendors? do they have any similar concept?
  5. Which devices, IOS support for this concept?
  • In general, not only on the cisco world, balance traffic by hash means that the system/appliance balance the traffic by using the hash of some fields of IP or TCP/UDP or a combination depending on the implementation of the hash, that's my understanding. – camp0 Jul 10 at 6:33
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What does Load balancing Hash mean in CEF?

The hash is an algorithm that determines which packet takes which path. Typically, it uses the source and destination IP addresses, but you can change which algorithm is used in order to modify the behavior. This is proprietary, so you really do not have the details. CEF has a few algorithms, but you should only change the algorithm with the ip cef load-sharing algorithm command if you really know what you are doing.

Which commands are use to configure?

You enable CEF with the ip cef command, and there is an optional distributed keyword for routers that can distribute it across multiple slots or processors. On the interfaces, you can use the ip load-sharing per-destination or ip load-sharing per-packet commands. Per-packet load sharing is not appropriate for everything, and it should only be used if you know that your traffic can handle it, but it will kill real-time traffic, e.g. VoIP.

Is it support to other vendors except Cisco? If it is not support other vendors? do they have any similar concept?

CEF is proprietary to Cisco, but other vendors may (or may not) have their own similar forwarding schemes.

Which devices, IOS support for this concept?

Basically, any Cisco router running IOS 12 or later. CEF was introduced on some routers in some IOS 11 versions.


Cisco has various documents explaining CEF. For example, IP Switching Cisco Express Forwarding Configuration Guide.

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