[Dshield] Blocking Country Access

Johannes B. Ullrich jullrich at sans.org
Tue Feb 20 20:15:16 GMT 2007

Andrew Willy wrote:
> Is this pretty common?  I've considered blocking networks for nations we
> don't expect traffic from but never followed through.

not "Very common". But its popular in particular as an anti-spam thing.

If you do this: make sure you don't have any legitimate business in
these countries. Think at cases like oversees US service personal for

It usually best to first log traffic for a while or compare your
proposed blocklist to historic traffic. But overall, it can help.

Most important: keep reviewing the list. I know one case where a
business planned to expand to asia, but ran into problems exchanging
e-mails with new partners due to a spam filter blocking asia. (as
always: you need to stay in touch with the business site to do your
security job well).

Johannes Ullrich                        http://isc.sans.org

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