nanog mailing list archives
Re: Anycast 101
From: Crist Clark <crist.clark () globalstar com>
Date: Thu, 16 Dec 2004 17:18:12 -0800
Steven M. Bellovin wrote:
In message <41C222C3.9020906 () globalstar com>, Crist Clark writes:Iljitsch van Beijnum wrote:Due to limitations in the DNS protocol, it's not possible to increase the number of authoritative DNS servers for a zone beyond around 13.I believe you misspelled, "Due to people who do not understand the DNS protocol being allowed to configure firewalls..."No, firewalls have nothing to do with it. Section 4.2.1 of RFC 1035 says:Messages carried by UDP are restricted to 512 bytes (not counting the IP or UDP headers).There's a large installed base of machines that conform to that limit and don't understand EDNS0. I'll leave the packet layout and arithmetic as an exercise for the reader (cheaters may want to run tcpdump on 'dig ns .' and examine the result), but the net result is what Iljitsch said: you can only fit about 13 servers into a response.
Into a UDP response. A resolver will recieve the first 512 bytes of the truncated response and may then use TCP to get the complete response... unless there is a firewall blocking 53/tcp in the way. But how often does that happpen? The root servers sustaining the ensuing SYN flood is another issue. -- Crist J. Clark crist.clark () globalstar com Globalstar Communications (408) 933-4387
Current thread:
- Anycast 101 Iljitsch van Beijnum (Dec 16)
- Re: Anycast 101 Crist Clark (Dec 16)
- Re: Anycast 101 Steven M. Bellovin (Dec 16)
- Re: Anycast 101 Crist Clark (Dec 16)
- Re: Anycast 101 Valdis . Kletnieks (Dec 17)
- Re: Anycast 101 Douglas K. Fischer (Dec 23)
- Re: Anycast 101 Steven M. Bellovin (Dec 16)
- Re: Anycast 101 Suzanne Woolf (Dec 16)
- Re: Anycast 101 Alon Tirosh (Dec 16)
- Re: Anycast 101 Crist Clark (Dec 16)
- Re: Anycast 101 Stephane Bortzmeyer (Dec 17)
- Re: Anycast 101 Iljitsch van Beijnum (Dec 17)
- Re: Anycast 101 Michael . Dillon (Dec 17)
- Re: Anycast 101 Marshall Eubanks (Dec 17)
- Re: Anycast 101 William Allen Simpson (Dec 17)