3Com S7902E, Configuration Manual

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1-6
An IRF typically has a daisy chain connection, that is, IRF-port1 of a device is connected to IRF-port2 of
another device, and the two devices are connected to form a single straight connection, as shown in
Figure 1-5 .
Figure 1-5 Physical connections of IRF
IRF-port1
IRF-port2
IRF
Master Slave
The orange line in the figure represents the IRF link, which is different from a common Ethernet network
cable. An IRF link can be composed of either one physical cable or multiple physical links.
Topology Collection
Each member in an IRF exchanges hello packets with the directly connected neighbors to collect
topology of the entire IRF. The IRF hello packets carry topology information, including IRF port
connection states, member IDs, priorities, and bridge MAC addresses.
Each member is managed by its local active SRPU, which records its known topology information
locally. At the initiation of the device startup, the local active SRPU records topology information of the
local device. When an IRF port of a member becomes up, the local active SRPU performs the following
operations:
1) Sends its known topology information from this port periodically.
2) Upon receiving the topology information from the directly connected neighbor, it updates the local
topology information.
3) If there is a local standby SRPU configured, the local active SRPU synchronizes its recorded
topology information to the local standby SRPU to ensure that the topology information on both
SRPUs is consistent.
After topology collection lasts for a period of time, all members have obtained the complete topology
information (known as topology convergence), and then the IRF will enter the next stage: role election.
Role Election
The process of defining the role (master or slave) of IRF members is role election.
Role election is held when the topology changes, such as, forming an IRF, adding a new member,
leaving or failure of the master, or IRF merge. The role election principles are as follows:
z
The current master wins, even if a new member has a higher priority. (When an IRF is being formed,
there is no master, and all member devices consider themselves as the master, so this principle will
be skipped)
z
A member with a higher priority wins.
z
A member with the longest system up-time wins. (The system up-time information of each device is
delivered through IRF hello packets)
z
A member with the lowest bridge MAC address wins.
The master is elected according to the above principles one by one, until the only winner is found out.