Local-Area Networks and LAN Switching - CCIE Routing and Switching Exam Certification Guide - page 140

RIF Max Frame Size Values Table 4-9

RIF MTU Bit Value Max Frame Size (bytes)

000 512

001 1500

010 2052

011 4472

100 8144

101 11407

110 17800

The lower 4 bits are not used.

The route descriptors are 2 bytes long. The first 12 bits indicate the ring number. The 4 least-
significant bits indicate the bridge number.

Figure 4-23 shows Token Ring and bridge numbers between Hosts A and B. Some numbers are
in decimal and others are in hexadecimal format.

RIF Example Figure 4-23

Host A Ring 20 Bridge 12 Ring 3 Bridge 10 Ring 0x10 Host B

The RIF header from Host A to Host B is constructed as follows:

00001000 00110000 = 0x0830

From the bits, you can determine the following:
•

This is a regular frame (type = 00).

•

It is 8 bytes in length (length = 01000).

•

The maximum frame size is 4472 (MTU = 011).

•

The direction bit is set to 0.

The route descriptors are constructed as follows. The last bridge number is set to 0x0:

Ring 20 (0x014) to Bridge 12 (0xC) to Ring 0x003 to Bridge 10 (0xA) to Ring (0x010) =
014c.003A.0100