Second Default Route

Answered Question
Feb 4th, 2010
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I have a 3750G connected up to two 6500's/  Port G1/0/25 goes to CoreA and G1/0/26 goes to CoreB


I have the following VLANs;


interface Vlan10
ip address 172.30.194.190 255.255.255.192
!
interface Vlan27
ip address 192.168.70.2 255.255.255.252
!
interface Vlan30
ip address 192.168.70.6 255.255.255.252



I have interface 1/0/25 configured in access vlan 27 and 1//0/26 in access vlan 30.


I currently have


ip route 0.0.0.0 0.0.0.0 192.168.70.1 (this points to CoreA)


I would like to add a second default route of:


ip route 0.0.0.0 0.0.0.0 192.168.70.5 250 (which would point to CoreB with a higher admin distance)


The question is whether or not this would provide the redundancy I am looking for.  If my cable is pulled on 1/0/25 will the second route take over?


James

Correct Answer by Jerry Ye about 7 years 4 months ago

Your config looks fine on your first post.


What I mean is you want to make sure your Core-B has a static route back to the 3750 for VLAN 10 (I am assuming you have a static route back on Core-A already).


Regards,

jerry

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Jerry Ye Thu, 02/04/2010 - 08:51
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Yes, just make sure you have a return route from Core B to the 3750 for VLAN 10.


Regards,

jerry

jfraasch Thu, 02/04/2010 - 08:54
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Jerry,


Thanks for the response.


Does the route need to be pointed to a VLAN instead of the upstream IP to make the failover happen?


ip route 0.0.0.0 0.0.0.0 VLAN27


and

ip route 0.0.0.0.0 0.0.0.0 VLAN 30 250


Or will it just know that it is down?


James

Correct Answer
Jerry Ye Thu, 02/04/2010 - 09:05
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Your config looks fine on your first post.


What I mean is you want to make sure your Core-B has a static route back to the 3750 for VLAN 10 (I am assuming you have a static route back on Core-A already).


Regards,

jerry

jfraasch Thu, 02/04/2010 - 09:08
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Thanks. That's what I thought.  I wish the customer would just allow a routing protocol.  Would be much easier than me having to guess.


Will test tomorrow.


James

kschleppenbach Thu, 02/04/2010 - 12:16
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What mechanism would take his first static route out of the routing table?

Jerry Ye Thu, 02/04/2010 - 12:54
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HI kschleppenbach, good catch, +5 for you


James, one question for you, are VLAN 27 and VLAN 30 on a trunk port? If they are on a trunk port and the remote is down, the default will not withdraw from the routing table without some type of IPSLA.


If VLAN 27 and VLAN 30 is the not on a trunk and just dedicated to port for the remote switch, why don't you make it a routed port (no switchport). Or better yet, use dynamic routing protocol.


Regards,

jerry

jfraasch Thu, 02/04/2010 - 13:02
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I just tested in my lab. It works great.  Here is an email I just sent out with the results:



In normal production you can see that there are routes to all the directly  connected networks and specifically there is a "gateway of last resort" set to  the primary route as shown below (note  this is a lab environment so not all production VLANs are  represented):
Gateway of last resort is  192.168.70.1 to network 0.0.0.0
     172.30.0.0/24 is subnetted, 1  subnets
C       172.30.192.0 is directly connected, Vlan2
      192.168.70.0/30 is subnetted, 2 subnets
C       192.168.70.4 is directly  connected, Vlan30
C       192.168.70.0 is directly connected, Vlan27
S*    0.0.0.0/0 [1/0] via 192.168.70.1
Now,  when I unplug the cable in port G1/0/47 which is in access vlan 27, the output  of the show ip route command is as follows:
Gateway of last resort is 192.168.70.5 to network  0.0.0.0
      172.30.0.0/24 is subnetted, 1 subnets
C       172.30.192.0 is directly  connected, Vlan2
     192.168.70.0/30 is subnetted, 1 subnets
C        192.168.70.4 is directly connected, Vlan30
S*   0.0.0.0/0 [250/0] via  192.168.70.5
Here  you can see that the default gateway has automatically failed over to  192.168.70.5 and that VLAN27 has been completely removed from the routing table.  The failover was immediate. As soon as the port goes down the routing table is  updated.

The ports are not trunked...they are just access ports.  So in the event of the link going down on the port associated with VLAN27, the failover will happen.

James
Jerry Ye Thu, 02/04/2010 - 13:14
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Thanks for the update James.


Regards,

jerry

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