December 2005
Intermediate to advanced
1066 pages
33h 38m
English
Content preview from Understanding Linux Network InternalsBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Proxy ARP
In the section "Processing Ingress ARP Packets," we saw how requests
for local addresses were handled by arp_process. Now we
will see how and when requests for remote addresses are handled by the same function.
We saw in the sections "Conditions
Required by the Proxy" in Chapter 26
and "Per-Device Proxying and Per-Destination
Proxying" in Chapter 27, that the
kernel supports two types of proxying : device-based and
destination-based (or global). Per-device proxy ARP is disabled on a host by default. It
can be enabled either globally or on a per-device basis via the /proc interface. The kernel can check whether proxying ARP is enabled on a
given device through the IN_DEV_PROXY_ARP macro defined
in include/linux/inetdevice.h. Per-destination
proxying can be configured with either the arp or the
ip neigh command (see the section "System Administration of Neighbors" in
Chapter 29).
ARP adds one more condition under which it does proxying: Destination Network Address Translation. We will see in the section "Destination NAT (DNAT)" why the kernel needs to proxy requests when DNAT is configured.
For an ARPOP_REQUEST to be eligible for handling by
a proxy server, the following conditions must be true:
Forwarding is enabled on the receiving device, or globally on the proxying host.
The target IP address is unicast (because other address types don't need ARP to be resolved, as we saw in the section "Special Cases" in Chapter 26). In code terms,
addr_type==RTN_UNICAST.The device receiving ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.