Lab 9-9: IS-IS Backbone and Leaf Area

As mentioned, IS-IS directly uses Layer 2, not IP, for protocol communication. The sniffer trace in Example 9-27 verifies this statement.

Example 9-27. Sniffing IS-IS Traffic

[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.

Example 9-28. IS-IS Area Configuration

callisto-isisd# configure terminal

callisto-isisd(config)# router isis DEAD

callisto-isisd(config)# net 49.0002.1921.6801.4001.00