Common operational misconceptions

Andrew Jones aj at
Mon Feb 20 04:09:34 UTC 2012

On Mon, 20 Feb 2012 11:17:32 +0900, Masataka Ohta
<mohta at> wrote:
>    draft-ohta-urlsrv-00.txt
>    DNS SRV RRs of a domain implicitly specify servers and port numbers
>    corresponding to the domain.
>    By combining URLs and SRV RRs, no port numbers have to be specified
>    explicitly in URLs, even if non-default port numbers are used, which
>    makes URLs more concise for port based virtual and real hosting,
>    where port based real hosting means that multiple servers sharing an
>    IP address are distinguished by port numbers to give service for
>    different URLs, which is the case for port forwarded servers behind
>    NAT and servers with realm specific IP.

It seems to me that this will create all sorts of headaches for firewall
ALGs. Rather than just passing port 21/tcp traffic to the FTP ALG for
example, the devices would need to inspect traffic on all ports and perform
DPI. This is not as much of a problem on the firewall protecting the
servers (you know what ports to inspect), but will require a lot more
processing power on the client-side NAT firewall.


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