Is the structure of IPv6 mtree similar with the IPv4 mtree structure? Have you guys seen any documentation about this subject?

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    Aug 11, 2017 at 2:07

1 Answer 1


What makes you think CEF uses an mtree? It is Optimum Switching that uses an mtree, not CEF.

How to Choose the Best Router Switching Path for Your Network

Optimum Switching

Optimum switching stores the forwarding information and the MAC header rewrite information in a 256 way multiway tree (256 way mtree). Using an mtree reduces the number of steps which must be taken when looking up a prefix, as illustrated in the next figure.

Cisco Express Forwarding

Cisco Express Forwarding, also uses a 256 way data structure to store forwarding and MAC header rewrite information, but it does not use a tree. Cisco Express Forwarding uses a trie, which means the actual information being searched for is not in the data structure; instead, the data is stored in a separate data structure, and the trie simply points to it.

I suppose it depends on what you mean by similar trie structure. Both IPv4 and IPv6 use a 256-way trie, and the data are stored in separate tables. In fact, the separate data structure for the MAC header rewrite information are nearly identical, except for minor things like the ethertype, since MAC headers don't care much about the upper-layer protocols.

  • Sorry I quoted from memory, I think it is trie not mtree
    – MiniMe
    Apr 28, 2016 at 20:42
  • The CEF can't be the same. ipv4 has 4 octets, IPV6 has 16 octets...that means that there should be at least 16 levels of that trie witch slows down the lookup process...
    – MiniMe
    Apr 29, 2016 at 0:47

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