08-14-2010 08:55 AM - edited 03-04-2019 09:25 AM
I have two sites connected via a Point to Point T1 link. In each side of the point to point link I have two different subnets (i.e. 192.168.2.0 and 192.168.3.0). I have a a full copy of each other on each side of the link (just in case it goes down). At both ends of the PTP link I have a cisco router. I understand that If I have both the serial and the ethernet interfaces plugged in at the same time, the router will always use the Ethernet interface, because it is a directly connected network. Can I still set it up with two paths to the same place (ethernet and serial) and leave the ethernet connection disconnected until it needs to be up? In other words, my serial link goes down, so I plug in my ethernet interface to the standby network and bring it up.
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08-14-2010 10:14 AM
Hello,
If it is directly connected network, then you cannot force the router to
send the traffic over T1 link. What I was suggesting is possible if the
router is routing over Ethernet link as well (Ethernet link should have
address other than 192.168.x.x address).
Regards,
NT
08-14-2010 09:09 AM
Hello,
If I understand you right, your network topology is something like below:
192.168.2.0 -- RTR ======T1/Ethernet====== RTR -- 192.168.3.0
If the network is as above, you do not need to disconnect the Ethernet
cable. You can use static routes and force the traffic to go over T1 and use
Ethernet only when T1 goes down:
ip route 192.168.x.0 255.255.255.0 254
Now, since the ethernet metric (cost) is higher than the T1, it will be used
only when T1 is down. Alternatively, you can also use a routing protocol and
increase the cost of the Ethernet link.
Hope this helps.
Regards,
NT
08-14-2010 09:23 AM
OK. So you can manipulate the router and tell it that the serial link has a lower metric (even-though it is not directly connected like the ethernet interface) than the ethernet interface? If so, what method would you use? Any specific routing protocol that would be better or can it be done using static routes?
08-14-2010 09:29 AM
Hello,
Can you please elaborate on what you mean by directly connected? Would it be
like:
192.168.2.0 -- RTR -
Ethernet (100.1.1.x)-- RTR -- 192.168.3.0
If that is how it is, then yes, you can configure the routing protocol like
RIP/EIGRP/OSPF and force the traffic to go through the other link.
Regards,
NT
08-14-2010 10:08 AM
I mean that when you have a network on a router's ethernet interface, it is going to put it on the routing t
able as a C route (directly connected), which by default has lowest metric (preferred route). You are saying that I can manipulate
that and give preference to the serial link to the network over the directly connected ethernet interface? If so, the routing will swap over to the other link
when the link goes down? And what about when the link comes back up? Should it recalculate and start routing over the preferred serial link?
08-14-2010 10:14 AM
Hello,
If it is directly connected network, then you cannot force the router to
send the traffic over T1 link. What I was suggesting is possible if the
router is routing over Ethernet link as well (Ethernet link should have
address other than 192.168.x.x address).
Regards,
NT
08-14-2010 10:37 AM
Thank You for your Replies NT.
08-14-2010 10:13 AM
You must not have the same subnet in different places. That prevents any basic routing and IP sane design to work.
Once you have remvoed the duplication, then you can do whatever you want.
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