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Chapter 11

Troubleshooting Switched Ethernet

such as the different Supervisor engines, and the RSM and NetFlow features. This
is also beneficial when isolating hardware-caused problems.

The Catalyst system uses a management bus to direct the switching process,

whereas the actual data packets use a separate 1.2Gb backplane. The manage-
ment bus operates at 761Kbps. These buses interconnect various cards within
the chassis for Ethernet, Token Ring, FDDI, and, in some cases, ATM.

SAMBA

The SAMBA ASIC is located on line modules and on the Supervisor mod-
ules. On the line cards, this chip is responsible for broadcast suppression,
based on thresholds established by the administrator. This ASIC also
maintains statistics on packets.

From a troubleshooting perspective, the SAMBA ASIC proves to be most

useful for obtaining various metrics to evaluate packet flow through the
switch. In addition, there may be instances when administrators wish to
suppress broadcast traffic on a threshold basis. Note that filtering broadcasts
on a port basis may cause problems for upper-layer protocols.

Cisco's SAMBA should not be confused with the SAMBA utility for providing

SMB (Windows NT) services on UNIX platforms.

SAINT

The SAINT (Synergy Advanced Interface and Network Termination) handles
Ethernet switching on the Catalyst 5000 platform, and it also handles ISL encap-
sulation. Each Ethernet port has an independent 192KB buffer for inbound and
outbound packets, which is divided to provide 168KB to outbound traffic and
24KB for inbound frames.

The ISL functionality is covered in another section of this chapter. Although

the buffer arrangement controlled by the SAINT has proven itself in hundreds
of networks and rarely presents a troubleshooting issue, administrators must
always consider buffer overflows and underruns as a factor. Again, capturing
the appropriate counters with the show commands provides the administrator
with troubleshooting tools.

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