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I  ran into an odd issue today – my firewall build script was failing on our account master node.

It turns out that I was trying to use a chain name in iptables that exceeded the maximum length allowed. I wanted to use "REMOTE_ACCOUNT_SLAV ES_ASHEVILLE" (31 chars) and the limit is 30 chars.

You can see this in /usr/include/linux/netfilter_ipv4/ip_tables.h and /usr/include/linux/netfilter/x_tables.h:

In my iptables configurations, I generally allow all traffic I am interested in and deny the rest, logging anything that is denied.

I found that this can get a bit noisy with loads of connections to udp:137 and udp:500, etc. so I decided to deny the more common ports without logging. But which are the most common ports?

Continue reading ‘Count of denied connections with iptables’ »