How rbridges work, Neighbor discovery, How rbridges work neighbor discovery – Brocade Network OS Administrator’s Guide v4.1.1 User Manual
Page 146
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Brocade Link Discovery Protocol (BLDP) attempts to discover if a Brocade VCS Fabric-
capable switch is connected to any of the edge ports. Refer to
on page
146 for more information.
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BLDP attempts to merge the adjacent Brocade switch into the Brocade VCS Fabric
environment at the link level.
• A series of FC fabric formation protocols (RDI, DIA, and FSPF) are initiated once a link level
relationship has been established between two neighbor switches. Refer to
page 147 for more information.
• The "Merge and Join" protocol invokes a merge of switch configuration between the cluster units
once the fabric has successfully formed.
How RBridges work
RBridges find each other by exchanging FSPF Hello frames. Like all TRILL IS-IS frames, Hello frames
are transparently forwarded by RBridges and are processed by RBridge Inter-Switch Link (ISL) ports.
Using the information exchanged in the Hello frames, the RBridges on each link elect the designated
RBridge for that link.
The RBridge link state includes information such as VLAN connectivity, multicast listeners, and
multicast router attachment, claimed nicknames, and supported ingress-to-egress options. The
designated RBridge specifies the appointed forwarder for each VLAN on the link (which could be itself)
and the designated VLAN for inter-RBridge communication. The appointed forwarder handles native
frames to and from that link in that VLAN.
The Ingress RBridge function encapsulates frames from the link into a TRILL data frame. The Egress
RBridge function decapsulates native frames destined for the link from the TRILL data frames. TRILL
data frames with known unicast destinations are forwarded by RBridge next hop. Multi-destination
frames (broadcast, unknown unicast, and multicast) are forwarded on a tree rooted at the multicast
root RBridge.
• Unicast forwarding is handled by combining domain routing generated by FSPF and MAC-to-
RBridge learning generated by MAC learning and a distributed MAC database.
• Multicast forwarding usually uses one tree that is rooted at the RBridge with the lowest RBridge ID.
However, there are several rules for Multicast root tree selection. It is not always the lowest RBridge
ID.
If a duplicated RBridge ID is found while the links are still coming up, the links are segmented. Both
sides recognize the error and segment the link. If the RBridge ID overlap cannot be found at ISL link
bringup time (in the case where a new switch is brought from an offline state into the fabric) it will be
found during the fabric build and the conflicting switch is isolated.
An RBridge requests a specific RBridge ID from the coordinator switch. If the coordinator switch
detects that this RBridge ID is already used, it returns the next unused RBridge ID. The requesting
RBridge is not allowed to take another RBridge ID and it segments itself from the fabric. In this case,
you cannot boot the ISLs. The ISLs have to be explicitly disabled and then enabled again in order for
the RBridge with the overlapping RBridge ID to be removed.
Neighbor discovery
Brocade VCS Fabric-capable neighbor discovery involves the following steps:
• Discover whether the neighbor is a Brocade switch.
• Discover whether the Brocade neighbor switch is Brocade VCS Fabric-capable.
Only Brocade VCS Fabric-capable switches with the same VCS ID can form a virtual cluster switch.
The default settings for Brocade Network OS switches are Brocade VCS Fabric capable and a VCS ID
of "1."
How RBridges work
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