Cisco Catalyst X4232 Installation And Configuration Note page 36

Overview of the Catalyst 4003 and 4006 Layer 3 Services Module Interfaces
Layer 3-switching software uses source + destination-based load balancing, an enhanced version of the
Cisco IOS software is per-destination load balancing. This method takes certain bits from the source
and destination IP and IPX addresses and maps them into a path.
This method has these benefits:
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Layer 3-switching software supports load balancing on equal cost paths using the source and destination
IP or IPX address. The Catalyst 4003 or 4006 Layer 3 Services module uses two equal cost paths.
Per-packet load balancing is not supported.
Optionally, if you are load balancing a Gigabit Ethernet port you may configure the port to load balance
using CEF.
CEF load balancing decisions are made on the ingress interface. Load distortions may occur across
multiple switch routers when the same CEF load balancing algorithm is used on every switch router.
You can resolve these distortions by selecting a specific CEF load balancing algorithm, such as tunnel
or universal, based on your network environment. The tunnel and universal algorithms are available on
Gigabit Ethernet ports only.
Hot Standby Router Protocol
The HSRP provides high network availability by routing IP traffic from hosts on Ethernet networks
without relying on the availability of any single switch router. This feature is particularly useful for
hosts that do not support a router discovery protocol and do not have the functionality to switch to a
new router when their selected router reloads or loses power.
Devices that are running HSRP detect a failure by sending and receiving multicast User Datagram
Protocol (UDP) "hello" packets. When HSRP detects that the designated active router has failed, the
selected backup router assumes control of the HSRP group's MAC and IP addresses. (You can also
select a new standby router at that time.)
The chosen MAC address and IP addresses are unique and do not conflict with any others on the same
network segment. The MAC address is selected from a pool of Cisco MAC addresses. Configure the
last byte of the MAC address by configuring the HSRP group number. You also configure the unique
virtual IP address. The IP address must be specified on a single router within the same group. When the
HSRP is running, it selects an active router and instructs its device layer to listen on an additional
(dummy) MAC address.
Layer 3-switching software supports HSRP over 10/100 Ethernet, Gigabit Ethernet, and GEC.
Gigabit EtherChannel
GEC allows grouping of gigabit ports into a single multigigabit logical EtherChannel link. GEC
establishes a high-bandwidth connection between two Catalyst switch routers.
You can bundle up to two Gigabit Ethernet connections on the Catalyst 4000 Layer 3 Services module
as one logical link, which can provide up to 4-Gb aggregate capacity. If a failure of any one link is
detected, the packets are switched on the remaining active link in the GEC.
GEC uses a source-destination IP and IPX address load-balancing scheme for up to two ports in a
channel group on the Catalyst 4003 and 4006 Layer 3 Services module. Each channel group has its own
IP address.When you queue a packet to exit out of the port channel interface, the last two bits of the IP
source and destination address determine which interface in the channel the packet takes.
As with all EtherChannel technologies, all links share the traffic load within the bundled ports.
Installation and Configuration Note for the Catalyst 4000 Layer 3 Services Module
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The traffic is distributed more effectively.
There is almost no impact on the data path performance.
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