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10. Appendix A - Netmask, proxy arp and bridging

Here we view some Linux advantages in Wireless Internetworking.

Linux let you specify a netmask like for an interface which can help you assign IP addresses in to any interface you want, for example one in eth0, another in eth1 and so on...

This has not particularly side-effects.

In addition you have proxy arp setting under /proc/sys/net/ipv4/conf/ethx/proxy_arp where ethx if your interface.

If you "echo 1 > proxy_arp" you enable proxy_arp for that interface while with "echo 0 > proxy_arp" you disable it.

What's proxy_arp? Quickly proxy arp help you when you want a router answer to an ARP request if the destination address is in another interface of the linux router.

Example: ---- Linux router ---- 

To get this example working you should:

Without proxy-arp 

  1. In host to set as gateway
  2. In host to set as gateway
  3. pinging with success from any edge.

With proxy-arp 

  1. In host to set as gateway
  2. do not set gateway for host but enable proxy_arp for right interface of the router.
  3. pinging with success from any edge

Proxy-arp in 2. case let the linux router answer when you ping from host, saying that it has the host so it can answer for it. After, when the source start sending ICMP packet, Linux router knows that it have to redirect it to the real host

In Wireless network proxy arp can help you if you have many Linux boxes that acts as IP Forwarders and you wouldn't set to all hosts a number of static route.

You also can experiment Linux bridging in Wireless network:

  1. install a recent stable kernel
  2. download good bridge utils at http link or ftp link

Bridging should be more simple to manage.

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