Thread: Difference between ARP Cache and DNS cache?

ARP - Address Resolution Protocol.
DNS - Domain Name System.

ARP translates an IP adrress (e.g 192.168.0.1) to a MAC address (e.g. 00:11:12:13:14:15)
DNS translates a name (e.g. Example Web Page) to an IP address (e.g. 212.178.0.19)

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Mats

Originally Posted by namasteall2000

Hello - could someone guide me the differenc between ARP and DNS cache? I know ARP cache is for 10 minutes while DNS is for some days - but why?

Any guidance is apprecited.

Thanks

First, although ARP and DNS both map higher-level names to lower-level names, they are really quite different.

The DNS cache time is actually configurable by the domain owner. The reason the cache time is (usually) very long is because the Internet is much slower than a local network (at least traditionally). Domain->address mappings don't change very often, so a lower cache time would simply increase the number of DNS lookup requests on the Internet at large, with no real benefit. Note that this caching is hierarchical.

On the other hand, a LAN is (supposedly) fast, and the devices connected to the LAN may change frequently. In that case, it isn't harmful to have a much lower cache residence time.

In both cases, we suffer from "cache poisoning" attacks where an evil party can inject a false cache entry that can cause packets to be sent to the wrong destination. In that respect a lower cache residence time is better, because the poisoned entry will be purged sooner.

Originally Posted by gabeve

i need an answer urgently

You urgently need to read this whole thread.

Originally Posted by gabeve

i need an answer urgently

42 - that's a very useful answer

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Mats

Originally Posted by gabeve

hello please reply

No thanks. I checked the list of the most important people in the world and you weren't on it.