how many schemes

  • littone

    littone - 2006-11-07


    I'm new to this forum and new to the kernal programming. Can anyone tell me what schemes (e.g. round robin) are currently implemented in bonding for link aggregation (802.3ad) ?


    • Jay Vosburgh

      Jay Vosburgh - 2006-11-07

      In the current version of bonding, two balance algorithms (selected via the xmit_hash_policy option) are available for 802.3ad mode: layer2 and layer3+4.  The layer2 algorithm utilizes a simple XOR function applied to the MAC addresses to determine which slave is used to transmit a particular packet.  The layer3+4 algorithm uses TCP, UDP and IP protocol information (if available) to compute a slave to use for a given packet.  The exact computations of the two algorithms are described in the documentation, along with a minor caveat about using layer3+4 in 802.3ad mode.

      No round robin style of selection is available in 802.3ad mode; the 802.3ad standard requires that a given conversation (connection) not be striped across multiple interfaces, in order to preserve the order of the packets in the conversation.  Moving a given conversation from interface to interface requires some type of assurance than packets will not be delivered out of order; this would be impossible to do in a round robin type of algorithm.

      Note that bonding also supports link aggregation modes other than 802.3ad: it provides Etherchannel compatible modes (balance-rr, balance-xor) as well as unique modes (balance-alb, balance-tlb) that do not require special support from the switch.


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