Secondary nameserver not in record - possibly dumb question about this..

[Peter Rose]

Hello,

I apologise if this is a very silly question, but please bear with me:

A friend of mine has recently set up his own server on a fast home link
with one IP.
His ISP is responsible for the DNS and the two nameservers listed in
Network Solutions registry are:

bambam.swlink.net
dino.swlink.net

I ran dig on his domain (usscreen.com) querying both nameservers and got
these results:


[peter at server peter]$ dig @bambam.swlink.net usscreen.com any

; <<>> DiG 8.3 <<>> @bambam.swlink.net usscreen.com any
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 1, ADDITIONAL: 2
;; QUERY SECTION:
;;      usscreen.com, type = ANY, class = IN

;; ANSWER SECTION:
usscreen.com.           1D IN MX        10 mail.usscreen.com.
usscreen.com.           1D IN MX        20 mail.usscreen.com.
usscreen.com.           1D IN NS        bambam.swlink.net.
usscreen.com.           1D IN SOA       usscreen.com.
hostmaster.swlink.net. (
                                        2000122701      ; serial
                                        3H              ; refresh
                                        1H              ; retry
                                        1W              ; expiry
                                        1D )            ; minimum

usscreen.com.           1D IN A         209.144.201.106

;; AUTHORITY SECTION:
usscreen.com.           1D IN NS        bambam.swlink.net.

;; ADDITIONAL SECTION:
mail.usscreen.com.      1D IN A         209.144.201.106
bambam.swlink.net.      1D IN A         204.252.163.69

;; Total query time: 178 msec
;; FROM: server to SERVER: bambam.swlink.net  204.252.163.69
;; WHEN: Thu Feb 22 16:57:16 2001
;; MSG SIZE  sent: 30  rcvd: 2

==============================================
Now, I know it's a mess (why have they got the same MX record for 10 and
20 preferences? Why do they have an A record for one of their machines
in their?), but when I was trying to explain WHY it's a mess, I
struggled a bit - after all, all his mail and web sites are working
fine.
The fact that there is only one nameserver shown in each record is
obviously a no-no - but I realised I didn't fully understand why this
is.
Both dino and bambam obviously answer queries regarding usscreen.com,
but does the absence of a record for dino in the files mean that if
bambam goes down, dino can't answer?
What I am trying to say is I guess I don't understand fully the process
of information propagating around the internet.

I'm trying to tell my friend his ISP has apparently got it wrong, but I
can't quite explain what the dire consequences are...

Any monosyllabic explanations welcome - or reference to the appropriate
page in DNS and BIND in case I've overlookd it.

TIA

Peter Rose
London UK