RFC1101, network info in DNS. Usefull ?
Marc_Lampo at hotmail.com
Marc_Lampo at hotmail.com
Mon Jan 24 15:46:56 UTC 2000
Thanks, an interesting example and easy to see the benifit in the output
of "netstat -r".
However, you seem to be defining A-records at the subnet-level itself.
Whereas rfc1101 attaches the A-record to the surrounding subnet.
According to the complicated example from rfc1101, I think it should
read :
; RFC1101 name and netmask entry for local net0
0.242.6.62.in-addr.arpa. IN PTR net0.rfc1035.com.
0.242.6.62.in-addr.arpa. IN A 255.255.255.248
; RFC1101 name and netmask entry for local net1
8.242.6.62.in-addr.arpa. IN PTR net1.rfc1035.com.
;8.242.6.62.in-addr.arpa. IN A 255.255.255.248
; RFC1101 name and netmask entry for local net2
16.242.6.62.in-addr.arpa. IN PTR net2.rfc1035.com.
;16.242.6.62.in-addr.arpa. IN A 255.255.255.248
; RFC1101 name and netmask entry for local net3
24.242.6.62.in-addr.arpa. IN PTR net3.rfc1035.com.
;24.242.6.62.in-addr.arpa. IN A 255.255.255.248
Since the .8, .16 and .24 are not further subnetted, they do not require
additional A-records (but kind of "inherit" the A-record from the
surrounding "class C" (0.242.6.62.in-addr.arpa)
Further according to that RFC1101, an A-record would be required at
surrounding net :
0.0.0.62.in-addr.arpa. A 255.255.255.0
The potential problem I see and to which I was referring at in my
original posting, rises when that 62.0.0.0/8 network is variably length
subnetted. eg
62.8.0.0/16 to organization1
62.6.242.0/27 to organization2
This would require 2 A-records at "top level"
0.0.0.62.in-addr.arpa. A 255.255.0.0
A 255.255.255.224
In the example from rfc1101, the "subnet 0" is not used. So the A-RR at
that level helps to locate the other subnets. But what would happen if
that subnet 0 were itself subnetted is left "undefined".
Marc
>
> Well the resolver code in BIND can use it. If there's an A record for
> the net's subnet mask in the reverse zone file, you get a /N appended
> to the netname in the output from netstat -r. This /N is the number of
> bits in the netmask.
>
> Here's an actual example from my own DNS data. I've only been assigned
> 32 addresses (62.6.242.0/27), but tell lies to my local name servers
> by pretending to be master for the whole 242.6.62.in-addr.arpa
> zone. The real reverse zone belongs to my ISP and only has CNAMEs, so
> I couldn't put PTR and A records there for my internal nets.
>
> Here are the relevant bits of the (internal) zone file:
>
> ; RFC1101 name and netmask entry for local net0
> 0.242.6.62.in-addr.arpa. IN PTR
net0.rfc1035.com.
> 0.242.6.62.in-addr.arpa. IN A 255.255.255.248
> ; RFC1101 name and netmask entry for local net1
> 8.242.6.62.in-addr.arpa. IN PTR
net1.rfc1035.com.
> 8.242.6.62.in-addr.arpa. IN A 255.255.255.248
> ; RFC1101 name and netmask entry for local net2
> 16.242.6.62.in-addr.arpa. IN PTR
net2.rfc1035.com.
> 16.242.6.62.in-addr.arpa. IN A 255.255.255.248
> ; RFC1101 name and netmask entry for local net3
> 24.242.6.62.in-addr.arpa. IN PTR
net3.rfc1035.com.
> 24.242.6.62.in-addr.arpa. IN A 255.255.255.248
>
> And here's what netstat has to say for itself on a host that's
> connected to two subnets:
>
> % netstat -r
> Routing tables
>
> Internet:
> Destination Gateway Flags MTU
If
> default router UGS 1500
ne0
> net0.rfc1035.com/29 link#2 UC 1500
ne0
> router 0:d0:58:e0:3c:bd UHLc 1500
ne0
> gromit 0:20:18:3a:fb:13 UHLc 1500
lo0
> net1.rfc1035.com/29 link#1 UC 1500
exp0
> gromit 0:a0:c9:e5:ea:8b UHLc 1500
lo0
> wallace 0:10:5a:ac:73:b6 UHLc 1500
exp0
> loopback-net localhost UGRS 4352
lo0
> localhost localhost UH 4352
lo0
> base-address.mcast.net/8 link#1 UC 1500
exp0
>
>
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