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I am using COM ports to connect to some hardware. I setup RAS connections for the various COM ports. If I connect to one device at a time then I am able to communicate using a TCP/IP socket with that device. When I establish a second connection using a second serial line to another device then the OS reports that the connection was setup successfully. However if I try to open a socket over this connection then it fails. When I try to ping the hardware devices I find that I can not reach either the first of the second device. If I now disconnect the first RAS connection I can now open a socket to the second device.

Windows XP does not share this problem. If I go through the same scenario with XP I can successfully open sockets to both devices at the same time.

The behaviour depends on the connections. Some connections appear to be independent. I can open 2 to 3 'independent' connections and then hit the problem on the next connection. When this happens the last connection will cause some of the earlier connections to fail. Again the failed connection and will stop responding to a ping. Removing When either of these 'dial-up' connections is disconnected its pair will work again.

I can see no pattern in the IP addresses of the 'paired' connections.

For example RAS connection with 192.168.245.141 will not work with RAS connection 192.168.245.116 but will work with the connection with IP address 192.168.245.113

I have looked at the properties of the connections and done ipconfig /all and can see no significant difference from XP. The only minor difference is that XP shows a standard physical address.

For Windows 7 the ipconfig /all output for the adapter is:

PPP adapter PROACTIV on COM17:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : PROACTIV on COM17

Physical Address. . . . . . . . . :

DHCP Enabled. . . . . . . . . . . : No

Autoconfiguration Enabled . . . . : Yes

IPv4 Address. . . . . . . . . . . : 192.168.245.141(Preferred)

Subnet Mask . . . . . . . . . . . : 255.255.255.255

Default Gateway . . . . . . . . . :

NetBIOS over Tcpip. . . . . . . . : Disabled

For XP it is

PPP adapter PROACTIV on COM17:

Connection-specific DNS Suffix . :

Description . . . . . . . . . . . : WAN (PPP/SLIP) Interface

Physical Address. . . . . . . . . : 00-53-45-00-00-00

DHCP Enabled. . . . . . . . . . . : No

IP Address. . . . . . . . . . . . : 192.168.245.141

Subnet Mask . . . . . . . . . . . : 255.255.255.255

Default Gateway . . . . . . . . . :

NetBIOS over Tcpip. . . . . . . . : Disabled

I would appreciate any help.

Russell

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migrated from stackoverflow.com Oct 4 '12 at 13:50

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1 Answer 1

After further investigation the cause of the problem appears to be that Windows 7 is only adding half the entries to the routing table and in particular is omitting the route from the PPP adapter to the device at the other end of the link.

I found that the PPP connections work if I manually run the command

route add 192.168.245.dd 192.168.245.pp

where 192.168.245.dd is the IP of the device

and 192.168.245.pp is the IP of the PPP adapter

This entry appears automatically in the routing table for XP when the connection is started but not for Windows 7.

Russell

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