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New Member

Routing IP subnet


Last week we have encountered a problme with slow e-mail access on one of the subnets on our network. We've done extensive troubleshooting. We've repalced the router, token ring switch, NIC on the e-mail server. Then we found out that if we change the ip address of that lan everything works fine. So the problem is either with an IP address or routing that particular ip address. Another thing is that from that subnet we were not able to telnet to some of the Unix machines that we have on the same subnet as e-mail server. I do not know if it is related or not.

Here is the topology.

TR-LAN---3600-----5505 with RSM-----3548---e-mai ser.


New Member

Re: Routing IP subnet

What was the old subnet/mask

whats the new subnet/mask

what shows up in the routing table(s) for both of the above ?

Was there any indication on the tokenring segment

of hard or soft errors ?

running any srb or dlsw on that seg?

New Member

Re: Routing IP subnet

1. old subnet - subnet -

3. I compared the routing table for the new subnet and the old one they looked identical. Both were routed the same.

4. I did not have any error on token ring interface

5. I am not running any sbr or dlsw on my network at all.

Last night I did a test where I pluged in am MAU directly into the router and pluged a laptop into the MAU and nothing else. It did exactly the same thing. It did not work with an old IP but it did work with a new one. Actually, it I can still send e-mail with old ip but it takes about a minute to send a message. However, I can download e-mails from e-mail esrver just fine.

With the new ip it works both ways.


Re: Routing IP subnet

The difference between the old and new subnet is following:

The new subnet is a part of Private Address Space (see RFC 1918) while the old one is not.


Milan Kulik

New Member

Re: Routing IP subnet

Possible arp issue? if so, maybe a faster timeout is in order across your devices.

New Member

Re: Routing IP subnet

Try ping -t using one subnet then the other. Do you lose any pings? Do the times differ?