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Configuring TRILL
TRansparent Interconnection of Lots of Links (TRILL) uses IS-IS to provide transparent Layer 2 forwarding.
TRILL requires a license. For information about feature licensing, see Fundamentals Configuration Guide.
Overview
TRILL combines the simplicity and flexibility of Layer 2 switching with the stability, scalability, and rapid
convergence capability of Layer 3 routing. All these advantages make TRILL very suitable for large flat
Layer 2 networks in data centers.
Basic concepts
• RBridge—Routing bridge (RB) that runs TRILL. RBs are classified into ingress RBs, transit RBs, and
egress RBs, depending on their positions in the TRILL network. A frame enters the TRILL network
through an ingress RB, travels along transit RBs, and leaves the TRILL network through an egress RB,
as shown in Figure 2.
• TRILL n
etwork—A Layer 2 network comprised of RBs, as shown in Figure 3.
• Sy
stem ID—Unique identifier of an RB in the TRILL network. The system ID is 6-byte.
• Nickname—Address of an RB in the TRILL network. The nickname is 2-byte.
• Link State Database—The LSDB contains all link state information in the TRILL network.
• Link State Protocol Data Unit—An LSP describes local link state information and is advertised
between neighbor devices.
• Designated Routing Bridge (DRB)—Similar to the designated IS (DIS) in IS-IS, a DRB exists in a
broadcast network. It helps simplify network topology, and assigns AVFs and appointed ports for
the VLANs on each RB in the broadcast network.
• Appointed VLAN-x Forwarder (AVF) and appointed port—To avoid loops, TRILL requires all traffic
of a VLAN on a broadcast network to enter and leave the TRILL network through the same port of
an RB. The RB is the VLAN's AVF, and the port is the VLAN's appointed port.
For more information about LSDB, LSPDU, and DIS, see Layer 3—IP Routing Configuration Guide.
TRILL frame formats
TRILL frames include protocol frames and data frames.
TRILL protocol frames include TRILL Hello, LSP, CSNP, PSNP, MTU-probe, and MTU-ack. These protocol
frames use 802.1Q encapsulation and have a fixed destination multicast address 0180-C200-0041.
TRILL data frames have a specific format, as shown in Figure 1. A TR
ILL header and an outer Ethernet
header are added to the original Ethernet frame.
