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Proxy ARP

ExtremeWare XOS 11.3 Concepts Guide

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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 commands:

enable iproute sharing

configure sharing address-based [L2 | L3]

Next, configure static routes and/or OSPF as you would normally.

BlackDiamond 10K Only. For the BlackDiamond 10K, ExtremeWare XOS supports route sharing across

up to 8 static routes and up to 8 ECMP routes for OSPF.

BlackDiamond 8800 family and Summit X450. For the BlackDiamond 8800 family and the Summit X450

switches, ExtremeWare XOS supports route sharing across up to 4 static routes and up to 4 ECMP

routes for OSPF.

Using route sharing makes router troubleshooting more difficult because of the complexity in predicting

the path over which the traffic will travel.

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 to simplify IP client configuration. The switch supports proxy ARP for this type

of network configuration. The section describes some example of using proxy ARP with the switch.

ARP-Incapable Devices

To configure the switch to respond to ARP requests on behalf of devices that are incapable of doing so,

you must configure the IP address and MAC address of the ARP-incapable device using the use the

following command:

configure iparp add proxy [<ipNetmask> | <ip_addr> {<mask>}] {vr <vr_name>} {<mac>}

{always}

After it is configured, the system responds to ARP requests on behalf of the device as long as the

following conditions are satisfied:

● The valid IP ARP request is received on a router interface.

● The target IP address matches the IP address configured in the proxy ARP table.

● The proxy ARP table entry indicates that the system should answer this ARP request, based on the

ingress VLAN and whether the

always parameter is set. When the always option is set, the switch

will ARP for the host even if the ARP requester is on the same subnet as the requested host. If the

always option is not set, the switch will only answer if the ARP request comes in from a VLAN that

is not on the same subnet as the requested host.

When all the proxy ARP conditions are met, the switch formulates an ARP response using the

configured MAC address in the packet.

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