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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: DNS problems to RoadRunner - tcp vs udp
Jon Kibler wrote: Various hardening documents for Cisco routers specify the best practices are to only allow 53/tcp connections to/from secondary name servers. Plus, from all I can tell, Cisco's 'ip inspect dns' CBAC appears to only handle UDP data connections and anything TCP would be denied. From what you are saying, the hardening recommendations are wrong and that CBAC may break some DNS responses. Is this correct? A number of Cisco default from years gone by would break DSN, today, in it's current form. Such as how PIXs and ASAs with fixup/DPI would block udp/53 packets larger than 512 bytes, not permitting EDNS packets through. Also, other than "That's what the RFCs call for," why use TCP for data exchange instead of larger UDP packets?
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