Reason for Limited number of Root DNS Servers

Warren Kumari warren at kumari.net
Fri Nov 11 06:08:23 UTC 2011


On Nov 11, 2011, at 1:38 PM, Gaurav Kansal wrote:

> Dear All,
>  
> Somewhere I read that number of ROOT DNS servers is limited to 13 because of protocol limitation of DNS and UDP.
> Exact writing was  “A combination of limits in the DNS and certain protocols, namely the practical size of unfragmented User Datagram Protocol (UDP) packets, resulted in a limited number of root server addresses that can be accommodated in DNS name query responses. This limit has determined the number of name server installations at (currently) 13 clusters, serving the needs of the entire public Internet worldwide.”
>  
> As root DNS are running in anycast so number is not an issue at all. 

Yes, but you still need the names ([a-m].root-servers.net) and the (anycasted) addresses for each...

dig NS @a.root-servers.net

; <<>> DiG 9.6.-ESV-R3 <<>> NS @a.root-servers.net
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45020
;; flags: qr aa rd; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 14
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;.				IN	NS

;; ANSWER SECTION:
.			518400	IN	NS	b.root-servers.net.
.			518400	IN	NS	g.root-servers.net.
.			518400	IN	NS	i.root-servers.net.
.			518400	IN	NS	m.root-servers.net.
.			518400	IN	NS	a.root-servers.net.
.			518400	IN	NS	j.root-servers.net.
.			518400	IN	NS	h.root-servers.net.
.			518400	IN	NS	d.root-servers.net.
.			518400	IN	NS	c.root-servers.net.
.			518400	IN	NS	l.root-servers.net.
.			518400	IN	NS	f.root-servers.net.
.			518400	IN	NS	e.root-servers.net.
.			518400	IN	NS	k.root-servers.net.

;; ADDITIONAL SECTION:
a.root-servers.net.	3600000	IN	A	198.41.0.4
a.root-servers.net.	3600000	IN	AAAA	2001:503:ba3e::2:30
b.root-servers.net.	3600000	IN	A	192.228.79.201
c.root-servers.net.	3600000	IN	A	192.33.4.12
d.root-servers.net.	3600000	IN	A	128.8.10.90
d.root-servers.net.	3600000	IN	AAAA	2001:500:2d::d
e.root-servers.net.	3600000	IN	A	192.203.230.10
f.root-servers.net.	3600000	IN	A	192.5.5.241
f.root-servers.net.	3600000	IN	AAAA	2001:500:2f::f
g.root-servers.net.	3600000	IN	A	192.112.36.4
h.root-servers.net.	3600000	IN	A	128.63.2.53
h.root-servers.net.	3600000	IN	AAAA	2001:500:1::803f:235
i.root-servers.net.	3600000	IN	A	192.36.148.17
i.root-servers.net.	3600000	IN	AAAA	2001:7fe::53

;; Query time: 122 msec
;; SERVER: 2001:503:ba3e::2:30#53(2001:503:ba3e::2:30)
;; WHEN: Fri Nov 11 05:59:32 2011

> But I don’t understand where exactly is this limitation exists???


;; MSG SIZE  rcvd: 512

^^^ Here!


>  
> Please some elaborate on this.
>  
>  
> Thanks and Regards,
> Gaurav Kansal
> 9910118448
>  
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