User guide

19
Release Notes for Cisco 2500 Series for Cisco IOS Release 12.0 T
78-5563-07 Rev.H0
New and Changed Information
For CBWFQ, the weight for a packet belonging to a specific class is derived from the bandwidth you
assigned to the class when you configured it. Therefore, the bandwidth assigned to the packets of a class
determines the order in which packets are sent. All packets are serviced fairly based on weight; no class
of packets may be granted strict priority.This scheme poses problems for voice traffic that is largely
intolerant of delay, especially variation in delay. For voice traffic, variations in delay introduce
irregularities of transmission manifesting as jitter in the heard conversation.
The Low Latency Queueing feature provides strict priority queueing for CBWFQ, reducing jitter in
voice conversations. Configured by the priority command, Low Latency Queueing enables use of a
single, strict priority queue within CBWFQ at the class level, allowing you to direct traffic belonging
to a class to the CBWFQ strict priority queue.
In the event of congestion, when the bandwidth is exceeded policing is used to drop packets. Voice
traffic enqueued to the priority queue is UDP-based and therefore not adaptive to the early packet drop
characteristic of Weighted Random Early Detection (WRED).
When congestion occurs, traffic destined for the priority queue is metered to ensure that the bandwidth
allocation configured for the class to which the traffic belongs is not exceeded.
Multicast Source Discovery Protocol
Multicast Source Discovery Protocol (MSDP) connects multiple PIM sparse-mode (SM) domains.
MSDP allows multicast sources for a group to be known to all rendezvous points (RPs) in different
domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains. An RP
runs MSDP over TCP to discover multicast sources in other domains.
An RP in a PIM-SM domain has an MSDP peering relationship with MSDP-enabled routers in another
domain. The peering relationship occurs over a TCP connection, where primarily a list of sources
sending to multicast groups is exchanged. The TCP connections between RPs are achieved by the
underlying routing system. The receiving RP uses the source lists to establish a source path.
The purpose of this topology is to have domains discover multicast sources in other domains. If the
multicast sources are of interest to a domain that has receivers, multicast data is delivered over the
normal, source-tree building mechanism in PIM-SM.
MSDP is also used to announce sources sending to a group. These announcements must originate at the
domain’s RP.
MSDP depends heavily on (M)BGP for interdomain operation. You should run MSDP in your domain’s
RPs that act as sources, sending to global groups for announcement to the Internet.
NetFlow Policy Routing
IP policy routing now works with Cisco Express Forwarding (CEF), Distributed CEF (DCEF), NetFlow,
and NetFlow with flow acceleration. IP policy routing was formerly supported only in fast-switching
and process-switching. Now that policy routing is integrated into CEF, policy routing can be deployed
on a wide scale and on high-speed interfaces.
SNA Switching Services
SNASw provides an easier way than earlier methods to design and implement networks with Systems
Network Architecture (SNA) routing requirements. Previously, this network design was accomplished
using Advanced Peer-to-Peer Networking (APPN) with full network node (NN) support in the Cisco
router. This type of support provided the SNA routing functionality needed, but was inconsistent with
the trends in Enterprise networks today. The corporate intranet is replacing the SNA WAN. Enterprises