ARP networking tricks

Be the first to comment | 3I like it!
on this topic
October 10, 2001, 10:23 AM —  Unix Insider — 

In March we introduced
the Address Resolution Protocol (ARP), a
half-brother to the TCP/IP stack that maps the logical IP address
space into the real world of Ethernet hardware addresses. We didn't
venture very far away from the safe confines of a local area network
and some simple troubleshooting, which is fine for introducing the
relationships of ARP to IP and various network broadcast activities,
but it doesn't describe the real real world very well. If
you're reading this, you've encountered a byzantine complex of hosts,
routers, desktops, and networks that will lay claim to some measure of
high availability, redundancy and well-ordered connectedness. To keep
the packets flowing from one end to the other, no matter what secret
packet vacuum networks you encounter on the way, you'll need to play
games with IP addresses or MAC addresses and fool clients' ARP
requests into believing your temporary version of network reality --
however cobbled together it might be.

This month we're going to complicate our simple explanation of ARP
with a closer look at stupid networking tricks, starting with the
interactions between the ARP family of protocols and the boot process.
We'll toss some routers into the fray, and look at ways of sending
packets to IP networks that aren't quite where the routers think they
are, and finally we'll show you how to run multiple IP networks on the
same physical network, a necessary strategy for most networking
transition and migration plans. We'll sprinkle hints and pointers
through this conclusion to dealing with things that go bump, ARP, or
otherwise collide in the night.

Double reverse slam-dunks: Reversing the ARP protocol

As we saw in my March column,
ARP is used to locate the hardware, or MAC address for a given IP
address. It takes the logical, 32-bit IP addresses like 192.9.200.1
and associates with it a 48-bit physical address like 8:0:20:45:7:b,
uniquely identifying the machine with the noted IP address. ARP is the
workhorse for establishing IP-level connections to new, previously
uncontacted hosts.

Sign up for ITworld's Daily newsletter
Follow ITworld on Twitter @IT_world

I like it!
Post a comment
The content of this field is kept private and will not be shown publicly.
  • Allowed HTML tags: <a> <em> <strong> <cite> <code> <ul> <ol> <li> <dl> <dt> <dd>
  • Lines and paragraphs break automatically.
peer-to-peer

Esther Schindler
If the comments are ugly, the code is ugly

claird
SVG a graphics format for 21st century

pasmith
Take Chrome OS for a test spin

Sandra Henry-Stocker
Solaris Tip: Have Your Files Changed Since Installation?

sjvn
64-bits of protection?

jfruh
Android fragments vs. the iPhone monolith

mikelgan
What Gizmodo missed about the Pro WX Wireless USB disk drive

 

Sidekick: The Good News & the Bad News
Either way you look at it Microsoft Data Center management did not follow standards or best practices in this failure. In which case it makes me wonder more about the outsourcing of corporate data much less personal data.
- mburton325

Join the conversation here

The Daily Tip

The Daily TipQuick, practical advice for IT pros. Made fresh daily.

Hot tips:

Want to cash in on your IT savvy? Send your tip to tips@itworld.com. If we post it, we'll send you a $25 Amazon e-gift card.

Newsletters

Subscribe to ITWORLD TODAY and receive the latest IT news and analysis.

I would like to receive offers via email from ITworld partners.
By clicking submit you agree to the terms and conditions outlined in ITworld's privacy policy.
Featured Sponsor

AISO founders envisioned a Web hosting company that was environmentally friendly. While the company employed energy-efficient innovations like solar panels, its infrastructure produced unacceptable power and cooling requirements. Find out how AISO leveraged AMD technology to overcome their challenge in this case study white paper.

In this whitepaper, Scalar explores the opportunity to change the landscape with respect to mission critical databases built around Oracle. Leveraging technologies such as Linux, high-end commodity processing power and Oracle RAC technology to architect, design, build and maintain database infrastructure that delivers maximum availability, reliability and performance at a fraction of traditional cost.

On a typical day, weather.com, the Web site for The Weather Channel in Atlanta, serves up between 15 million and 20 million page views. But in September 2004, when back-to-back hurricanes ransacked Florida, the peak traffic on one day more than tripled: over 70 million page views by more than 7 million unique visitors. Read the full success story now.

Marketplace