Linux-Cisco-ADSL-Cisco-Linux Connection hangs....

Hi guys..

Im having a strange problem with linux servers and cisco routers here
its my setup:


Linux Server---Cisco router---ADSL Link---Cisco router--- Linux Server


The strange stuff its that i can ping from one linux to the other with
no problems, but when i open a telnet session from one linux to the
other and type any command (ls, top, ifconfig, etc) the connection just
hangs and stays there forever.

If i open another telnet session to the linux server it works until the
command prompt (asks for login, password) and when i type any command
and enter, the connection hangs..

this its happening not just with telnet, pop3, smtp, any TCP connection
seems to work at first but later just hangs in there.

Can anyone share some light here..

Thanks..

 

Sounds like all the classic symptoms of a PMTUD black hole to me.

Running PPPoE on that ADSL line?

 

DNS..........possibly
When you open a connection to a server, that server may do a dns query
on the ip address to map it back to a fully qualified domain name.
So, here's the test. On the server you are trying to connect to, do
"nslookup x.x.x.x" where x.x.x.x is the other box's ip address.

 

this its happening not just with telnet, pop3,

Yes im running PPPoE

what its the PMTUD black hole, where i can get information about it ?

Thanks a lot guys..

 

in there. Can anyone share some light here.. Thanks..

I dont think so, because i can ping and get into the server, but when i
type any linux/unix command (ls, who, last, etc) the connection hangs.

Thanks..

 

Google is your friend. "PMTUD Black Hole" brings up useful info.

 

on your facing interface on both sides, put a policy to unset the
df bit.

example:

int f0/0
ip policy route-map clear-df-bit
access-list 101 permit ip any any
route-map clear-df-bit permit 10
match ip address 101
set ip df 0