Editing Dynamic routing (section)

== Alternate paths ==
Many systems use some [[hop (networking)#Next hop|next-hop]] forwarding protocol—when a packet arrives at some node, that node decides on-the-fly which link to use to push the packet one hop closer to its final destination.

Routers that use some adaptive protocols, such as the [[Spanning Tree Protocol]], in order to "avoid [[bridge loop]]s and [[routing loop]]s", calculate a tree that indicates the one "best" link for a packet to get to its destination.
Alternate "redundant" links not on the tree are temporarily disabled—until one of the links on the main tree fails, and the routers calculate a new tree using those links to route around the broken link.

Routers that use other adaptive protocols, such as '''grouped adaptive routing''', find a group of ''all'' the links that could be used to get the packet one hop closer to its final destination.
The router sends the packet out any link of that group which is idle.
The [[link aggregation]] of that group of links effectively becomes a single high-bandwidth connection.<ref>
Stefan Haas.
[http://inspirehep.net/record/887357/files/cer-002474543.pdf "The IEEE 1355 Standard: Developments, Performance and Application in High Energy Physics"].
1998.
p. 91.
</ref>