-----Original Message----- From: Matthew Reath [mailto:matt@mattreath.com] Sent: 07 February 2012 21:34 To: nanog@nanog.org Subject: Firewalls in service provider environments
All,
Looking for some recommendations on firewall placement in service provider environments. I'm of the school of thought that in my SP network I do as little firewalling/packet filtering as possible. As in none,
I had a vendor actually suggest that that ALL my customer traffic should traverse a firewall. I asked why and they said "Ahhh it the internet, must have firewall". I suppose this must have been a great firewall.
So yes I would agree with you, firewall nothing for your customers unless they are paying you for a specific service. Filtering known bad ports, well, what's a known bad port? Bad for one person may be quite important for another. Whilst filtering port 25 outbound may help prevent some bots from emanating spam, it certainly does a lot to annoy other people.
-- Leigh Porter
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From a filtering perspective there are some know worm ports and such that we usually have a template created for.
Here is the template we typically use (or a variant of it): <-- snippet --> access-list 102 deny ip 10.0.0.0 0.255.255.255 any access-list 102 deny ip 172.16.0.0 0.15.255.255 any access-list 102 deny ip 192.168.0.0 0.0.255.255 any access-list 102 deny ip 0.0.0.0 0.255.255.255 any access-list 102 deny ip 127.0.0.0 0.255.255.255 any access-list 102 deny ip 224.0.0.0 15.255.255.255 any access-list 102 deny ip host 255.255.255.255 any access-list 102 deny tcp any any eq 135 access-list 102 deny udp any any eq 135 access-list 102 deny udp any any eq netbios-ns access-list 102 deny tcp any any eq 139 access-list 102 deny udp any any eq netbios-ss access-list 102 deny tcp any any eq 445 access-list 102 deny tcp any any eq 593 access-list 102 deny tcp any any eq 4444 access-list 102 deny tcp any any eq 9996 access-list 102 deny tcp any any eq 5554 access-list 102 deny tcp any any eq 8888 access-list 102 deny tcp any any eq 7778 access-list 102 deny tcp any any eq 8594 access-list 102 deny tcp any any eq 8563 access-list 102 deny tcp any any eq 1434 <-- end snippet --> This blocks some common worm ports as well as traffic sourced outside of our network from reserved address space. -Matt