07-10-2007 04:23 PM - edited 03-03-2019 05:48 PM
I build two GRE tunnel with keepalive, and use floating static route for backup purpose. But i found it works improperly due to a route point to null0.
ip route 10.20.1.0 255.255.255.0 1.2.4.6
ip route 10.20.1.0 255.255.255.0 1.2.4.10 200
ip route 1.2.0.0 255.255.0.0 null0 --->this route caused floating static route works improperly. Even if the Tunnel500 is down, the route 10.20.1.0 to 1.2.4.6 will keeping active. But if i remove the route 1.2.0.0 to null0, it works fine. I got little confuse, anyone would help will be much appreciated.
!
interface Tunnel500
ip address 1.2.4.5 255.255.255.252
ip mtu 1500
ip tcp adjust-mss 1350
keepalive 5 1
tunnel source 10.86.2.2
tunnel destination 10.90.10.194
!
interface Tunnel501
ip address 1.2.4.9 255.255.255.252
ip mtu 1476
ip tcp adjust-mss 1436
keepalive 5 1
tunnel source 10.86.4.2
tunnel destination 10.90.10.198
Solved! Go to Solution.
07-11-2007 07:39 AM
Hi,
What is happening, is that in presence of "ip route 1.2.0.0 255.255.0.0 null0", the router is trying recursive routing, because the routing information for 1.2.4.6 is derived from the said static route.
To work around this, either use dynamic routing over tunnel, or point the static route to the interface and not IP address, or both IP address AND interface.
A good discussion is presented at:
http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a00800ef7b2.shtml
Hope this helps, please rate post if it does!
07-10-2007 04:33 PM
Can you send output of "show ip route 10.20.1.0 255.255.255.0" when tunnel500 is up, and again when it is down ?
And again the above, when "ip route 1.2.0.0 255.255.0.0 null0" is not configured.
07-11-2007 07:05 AM
r1#sh ip route 10.20.1.0 -------When "ip route 1.2.0.0 255.255.0.0 null0" is configured, no matter the tunnel500 is up or down, the "sh ip route 10.20.1.0" output will be the same
Routing entry for 10.20.1.0/24
Known via "static", distance 1, metric 0
Redistributing via ospf 1
Routing Descriptor Blocks:
* 1.2.4.6
Route metric is 0, traffic share count is 1
!
r1#sh ip route 10.20.1.0 ------- When tunnel500 is up and "ip route 1.2.0.0 255.255.0.0 null0" is not configured.
Routing entry for 10.20.1.0/24
Known via "static", distance 1, metric 0
Redistributing via ospf 1
Routing Descriptor Blocks:
* 1.2.4.6
Route metric is 0, traffic share count is 1
!
r1#sh ip route 10.20.1.0 ------- When tunnel500 is down and "ip route 1.2.0.0 255.255.0.0 null0" is not configured.
Routing entry for 10.20.1.0/24
Known via "static", distance 200, metric 0
Redistributing via ospf 1
Routing Descriptor Blocks:
* 1.2.4.10
Route metric is 0, traffic share count is 1
!
07-11-2007 07:39 AM
Hi,
What is happening, is that in presence of "ip route 1.2.0.0 255.255.0.0 null0", the router is trying recursive routing, because the routing information for 1.2.4.6 is derived from the said static route.
To work around this, either use dynamic routing over tunnel, or point the static route to the interface and not IP address, or both IP address AND interface.
A good discussion is presented at:
http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a00800ef7b2.shtml
Hope this helps, please rate post if it does!
07-11-2007 08:26 AM
p.bevilacqua,
It's greatly helpful. Thank you so much!!
I point the static route to IP address AND interface, it works fine.
ip route 10.20.1.0 255.255.255.0 Tunnel500 1.2.4.6
ip route 10.20.1.0 255.255.255.0 Tunnel501 1.2.4.10 200
07-11-2007 08:51 AM
In reality, the IP address is redundant, as your tunnel interfaces are point-to-point. But, it doesn't harm neither.
Thanks for the nice rating and good luck!
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