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194 Summit 200 Series Switch Installation and User Guide
IP Unicast Routing
NOTE
If you define multiple default routes, the route that has the lowest metric is used. If multiple default
routes have the same lowest metric, the system picks one of the routes.
You can also configure blackhole routes. Traffic to these destinations is silently dropped.
IP Route Sharing
IP route sharing allows multiple equal-cost routes to be used concurrently. IP route sharing can be used
with static routes or with OSPF routes. In OSPF, this capability is referred to as equal cost multipath
(ECMP) routing. To use IP route sharing, use the following command:
enable iproute sharing
Next, configure static routes and/or OSPF as you would normally. ExtremeWare supports unlimited
route sharing across static routes and up to eight ECMP routes for OSPF.
Route sharing is useful only in instances where you are constrained for bandwidth. This is typically not
the case using Extreme switches. Using route sharing makes router troubleshooting more difficult
because of the complexity in predicting the path over which the traffic will travel.
Subnet-Directed Broadcast Forwarding
You can enable or disable the hardware forwarding of subnet-directed broadcast IP packets. This allows
the switch to forward subnet-directed broadcast packets at wire-speed.
To enable or disable hardware forwarding, use the following command:
[enable | disable] ipforwarding fast-direct-broadcast [vlan <vlan_name>]
The entries are added to the IP forwarding table as standard entries and you can view them using the
show ipfdb command.
You can also configure the VLAN router interface to either forward and process all subnet-directed
broadcast packets, or to simply forward these packets after they have been added to the IP forwarding
database. The latter option allows you to improve CPU forwarding performance by having upper
layers, such as UDP and TCP, ignore broadcast packet processing (for example, if the packets have
IP-options configured).
To enable or disable broadcast packet processing, use the following command:
[enable | disable] ipforwarding ignore-broadcast vlan <vlan_name>
Proxy ARP
Proxy Address Resolution Protocol (ARP) was first invented so that ARP-capable devices could respond
to ARP Request packets on behalf of ARP-incapable devices. Proxy ARP can also be used to achieve
router redundancy and simplify IP client configuration. The switch supports proxy ARP for this type of
network configuration. The section describes some example of how to use proxy ARP with the switch.