Table of Contents
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| Introduction
C
1
HAPTER
Description of Software Features
E
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QUAL
COST
M
L
ULTIPATH
OAD
B
ALANCING
R
R
OUTER
EDUNDANCY
A
R
DDRESS
ESOLUTION
P
ROTOCOL
OSPF – This approach uses a link state routing protocol to generate a
shortest-path tree, then builds up its routing table based on this tree. OSPF
produces a more stable network because the participating routers act on
network changes predictably and simultaneously, converging on the best
route more quickly than RIP.
BGP – This protocol uses a path vector approach to connect autonomous
systems (AS) on the Internet. BGP maintains a table of IP network prefixes
which designate network reachability among autonomous systems based
the path of ASs to the destination, and next hop information. It makes
routing decisions based on path, network policies and/or rule sets. For this
reason, it is more appropriately termed a reachability protocol rather than
a routing protocol.
Policy-based Routing for BGP – The next-hop behavior for ingress IP traffic
can be determined based on matching criteria.
When multiple paths to the same destination and with the same path cost
are found in the routing table, the Equal-cost Multipath (ECMP) algorithm
first checks if the cost is lower than that of any other routing entries. If the
cost is the lowest in the table, the switch will use up to eight paths having
the lowest path cost to balance traffic forwarded to the destination. ECMP
uses either equal-cost unicast multipaths manually configured in the static
routing table, or equal-cost multipaths dynamically detected by the Open
Shortest Path Algorithm (OSPF). In other words, it uses either static or
unicast routing entries, not both.
The Virtual Router Redundancy Protocol (VRRP) uses a virtual IP address to
support a primary router and multiple backup routers. The backups can be
configured to take over the workload if the master fails or to load share the
traffic. The primary goal of this protocol is to allow a host device which has
been configured with a fixed gateway to maintain network connectivity in
case the primary gateway goes down.
The switch uses ARP and Proxy ARP to convert between IP addresses and
MAC (hardware) addresses. This switch supports conventional ARP, which
locates the MAC address corresponding to a given IP address. This allows
the switch to use IP addresses for routing decisions and the corresponding
MAC addresses to forward packets from one hop to the next. Either static
or dynamic entries can be configured in the ARP cache.
Proxy ARP allows hosts that do not support routing to determine the MAC
address of a device on another network or subnet. When a host sends an
ARP request for a remote network, the switch checks to see if it has the
best route. If it does, it sends its own MAC address to the host. The host
then sends traffic for the remote destination via the switch, which uses its
own routing table to reach the destination on the other network.
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