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very sluggish SSH when using over dialup ppp link

 
 
Tobias Skytte
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      08-17-2004, 10:06 AM
Hi,

I have an interresting (imho) problem with SSH. I am running a small
ISP server that has a 64K DSL connection. Whenever I connect to the
server via SSH (using a fine program called PuTTY) from another
computer connected to the server via a LAN it works just fine. But
when I connect to the server via dial-in the ssh almost doesn't work
at all. I usually have to attempt to login several times because it
decides that the time I spend between typing the login-name and the
password takes too long so it closes the connection. And when I
finally get in, it is so sluggish that almost unusable (i type some
characters and it takes sometimes several seconds, up to 10 secs, to
display) but then sometimes it seems to work faster (this comes in
waves). The computer I am dialing in from is not otherwise accessing
the internet so I don-t see how it can be a traffic-control problem as
there is no other data on the ppp link.
Secondly, the really weird part is that if my DSL link (from the
server to the internet) goes down then I can *not* get into the server
even from the LAN ! I merely get a timeout and have to physically
(urgh) go to the server and login there.
What gives?
The network layout is like this:

internet
|
|
cisco 1600
|
SERVER (eth0)
SERVER (eth1)
|
LAN

Server is running RH 9.
How come SSH is sensitive to wether eth0 is up or down? and how come
it works fine (when eth0 is up) over the LAN but not over a dial-in
link?
I can post logfiles if necessary but not sure which ones would be
interresting.
Any help much appreciated.

Regards,
Tobias Skytte
 
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chris-usenet@roaima.co.uk
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      08-17-2004, 12:29 PM
Tobias Skytte <(E-Mail Removed)> wrote:
> How come SSH is sensitive to wether eth0 is up or down?


Your server is trying to resolve the originating IP address to a name
by using DNS. If the link is down then DNS can't resolve the name. Your
SSH service appears to be configured to reject the connection attempt
if the DNS resolution fails.

> and how come
> it works fine (when eth0 is up) over the LAN but not over a dial-in
> link?


You've got your LAN clients either in /etc/hosts or in DNS or on a
"trusted" network.

You need to check your sshd_config for AllowUsers/DenyUsers, and
maybe /etc/hosts.allow and /etc/hosts.deny if ssh has been built with
tcp-wrappers. I'm not familiar with the particular configuration of SSH
on RH9 so I can't give you more specifics.

Chris
 
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Bill Unruh
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      08-17-2004, 04:02 PM
(E-Mail Removed) (Tobias Skytte) writes:

]Hi,

]I have an interresting (imho) problem with SSH. I am running a small
]ISP server that has a 64K DSL connection. Whenever I connect to the
]server via SSH (using a fine program called PuTTY) from another
]computer connected to the server via a LAN it works just fine. But
]when I connect to the server via dial-in the ssh almost doesn't work
]at all. I usually have to attempt to login several times because it
]decides that the time I spend between typing the login-name and the
]password takes too long so it closes the connection. And when I
]finally get in, it is so sluggish that almost unusable (i type some
]characters and it takes sometimes several seconds, up to 10 secs, to
]display) but then sometimes it seems to work faster (this comes in
]waves). The computer I am dialing in from is not otherwise accessing
]the internet so I don-t see how it can be a traffic-control problem as
]there is no other data on the ppp link.
]Secondly, the really weird part is that if my DSL link (from the
]server to the internet) goes down then I can *not* get into the server
]even from the LAN ! I merely get a timeout and have to physically
](urgh) go to the server and login there.
]What gives?
]The network layout is like this:

]internet
] |
] |
]cisco 1600
] |
]SERVER (eth0)
]SERVER (eth1)
] |
] LAN

]Server is running RH 9.
]How come SSH is sensitive to wether eth0 is up or down? and how come
]it works fine (when eth0 is up) over the LAN but not over a dial-in
]link?
]I can post logfiles if necessary but not sure which ones would be
]interresting.
]Any help much appreciated.

]Regards,
]Tobias Skytte

Sounds like it might be host name resolving problems. ssh uses the new
getaddrinfo dns routines for ipv6, which can sometimes do weird things. It
sounds like things are timing out on you.
ssh over a phone line should be slower once it is going, since the phone
link is slower. Not sure if it is anything but this.

 
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