As mentioned, IS-IS directly uses Layer 2, not IP, for protocol communication. The sniffer trace in Example 9-27 verifies this statement.
[root@callisto:~#] tethereal -V -i eth0
Frame 2 (1514 bytes on wire, 1514 bytes captured)
Arrival Time: Feb 4, 2003 14:31:44.653860000
Time delta from previous packet: 0.005838000 seconds
Time relative to first packet: 0.005838000 seconds
Frame Number: 2
Packet Length: 1514 bytes
Capture Length: 1514 bytes
IEEE 802.3 Ethernet
Destination: 01:80:c2:00:00:15 (ISIS-all-level-2-IS's)
Source: 00:e0:b0:6a:69:7e (Cisco_6a:69:7e)
Length: 1500
Logical-Link Control
DSAP: ISO Network Layer (0xfe)
IG Bit: Individual
SSAP: ISO Network Layer (0xfe)
CR Bit: Command
Control field: U, func = UI (0x03)
000. 00.. = Unnumbered Information
.... ..11 = Unnumbered frame
ISO 10589 ISIS InTRA Domain Routeing Information Exchange Protocol
Intra Domain Routing Protocol Discriminator: ISIS (0x83)
PDU Header Length : 27
Version (==1) : 1
System ID Length : 0
PDU Type : L2 HELLO (R:000)
Version2 (==1) : 1
Reserved (==0) : 0
Max.AREAs: (0==3) : 0
ISIS HELLO
Circuit type : Level 1 and 2, reserved(0x00 == 0)
System-ID {Sender of PDU} : 1921.6820.1002
Holding timer : 10
PDU length : 1497
Priority : 64, reserved(0x00 == 0)
System-ID {Designated IS} : 1921.6820.1002.01
Protocols Supported (1)
NLPID(s): IP (0xcc)
Area address(es) (4)
Area address (3): 49.0001
IP Interface address(es) (4)
IPv4 interface address : 192.168.14.254 (192.168.14.254)
Padding (255)
Padding (255)
Padding (255)
Padding (255)
Padding (255)
Padding (168)
Now we will put callisto in a different area. The only change necessary to assign callisto to area 2 as well is demonstrated in Example 9-28. Remember that the only factor that constitutes a backbone is a contiguous assembly of Layer 2 intermediate systems.
callisto-isisd# configure terminal callisto-isisd(config)# router isis DEAD callisto-isisd(config)# net 49.0002.1921.6801.4001.00