Specifications

Release Notes for Cisco IOS Release 12.0 S

78-7130-11 Rev. B0

New and Changed Information

Section Data Communications Channel

Platforms: Cisco 12000

On Cisco GSR OC-48 based line cards, Cisco IOS Release 12.0 S now supports the IP/Section Data

Communications Channel (SDCC) interface that is available on the Cisco OC-48 Optical Regenerator.

To enable this feature, enter the sdcc enable command in configuration mode. To disable this feature,

enter the no sdcc enable command. See the following document for further information:

http://www.cisco.com/univercd/cc/td/doc/product/core/optregen/opt_cfg/regen48.htm

SNMP Support for BGP Policy Accounting

Platforms: Cisco 7200 series, Cisco 7500/RSP series, Cisco 12000 series

BGP Policy Accounting accumulates incoming packet counts and octet counts per interface in the fibidb

structure. These counters are now SNMP retrievable because of a new MIB called

CISCO-BGP-POLICY-ACCOUNTING-MIB. Each row in the MIB table contains statistics for a

particular traffic type on an interface. The table is indexed by ifindex from the IF-MIB and a

traffic_index that identifies a particular traffic type. The traffic can be classified into one of eight types

using the command-line interface (CLI).

Weighted Random Early Detection

Platforms: Cisco 12000 series

Random Early Detection (RED) is a congestion avoidance mechanism that takes advantage of the TCP

congestion control mechanism. By randomly dropping packets prior to periods of high congestion, RED

tells the packet source to decrease its transmission rate. Assuming the packet source is using TCP, it

will decrease its transmission rate until all the packets reach their destination, indicating that the

congestion is cleared.

Weighted RED (WRED) generally drops packets selectively based on IP precedence. Packets with a

higher IP precedence are less likely to be dropped than packets with a lower precedence. Thus, higher

priority traffic is delivered with a higher probability than lower priority traffic. However, you can also

configure WRED to ignore IP precedence when making drop decisions so that nonweighted RED

behavior is achieved.

WRED is useful on any output interface where you expect to have congestion. However, WRED is

usually used in the core routers of a network, rather than at the edge. Edge routers assign IP precedences

to packets as they enter the network. WRED uses these precedences to determine how it treats different

types of traffic. See the following document for further information:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios112/ios112p/gsr/wred_gs.htm