telnet connection times

[Mark Duffy]

Hi all,

I have the following problem. We use ssh for connection to an N Class running 11.00 for most users but still allow telnet access for some. Those accessing via telnet do not have entries in our local hosts file or DNS. These users are experiencing delays of around 40 seconds before getting a connection. I've had our network team have a look at this problem and the have come up with the explanation detailed below. Could anyone shed any light on this problem? Is it possible to stop telnetd waiting for a reverse lookup response or limit it's wait time? I believe a local host file entry would sort the problem but the amount of entries would be large. I also presume entries in the DNS server would solve the problem but this would be a while down the line. I'm really looking for any sort of "quick fix".

All comments appreciated. Network team response is this:

"telnetd is trying to do a reverse lookup on inbound session IP addresses and cannot verify. The problem does not happen locally as all local hosts have dns entries, and associated reverse lookups for their IP's. WAN clients do not have reverse lookup entries on the dns servers that HOSTNAME uses, and we have no centralized dns solution as of yet to provide WAN lookups. Problem does not occur with ssh as ssh does not do a reverse lookup as the security is inherent within the encryption of ssh. As dns queries are udp, when the server tries to do a reverse lookup on the IP to the dns server, no yes/no reply is sent back, so the telnetd daemon waits for a certain length of time before assuming a no. This default time seems to be about 40s on HOSTNAME"

Cheers,

Mark

[Herve BRANGIER · Accepted solution]

Hi

Lookk at that :

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x6202a22d6d27d5118fef0090279cd0f9,00.html

If you have not a lot of local systems, you can
put all of them on your local hosts file and
disable use of DNS. In this case you have no
timeout to configure : request are local, if
there no line for an address in /etc/hosts
reply is immediate...
I made that by an ls on my own dns, I put all
entries in my file and it's ok. I update my
file with an ls on your nameserver...

HTH

Herv?

[Sachin Patel]

Hi Mark,
You can run a script that pulls all the data from remote centers and saves in to your DNS as CNAME.
Example:
yourdomain.com pulls data from remote1.com and remote2.com and saves all NS and A records on to yourdomain.com map as CNAME.

I have a perl script that does this for us.

[Sachin Patel]

Oppps I forget. I have attached script in my previous reply.

Sachin

[John Bolene]

Yes, the normal DNS timeoput is 40 seconds which is an eternity.

You can configure your /etc/nsswitch.conf file to look at files first and put all the telnetted terminal ids in the /etc/hosts file.