From: Jason Madsen (madsen.jason@gmail.com)
Date: Sun Jan 11 2009 - 18:53:01 ARST
it also appears his tunnel referenced F0/0 addresses for his endpoints and
not any loopbacks...the config' doesn't appear to be the "cleanest", but it
should work without recursion if in fact his F0/0 interfaces have /24
masks.
Jason
On Sun, Jan 11, 2009 at 1:44 PM, Jason Madsen <madsen.jason@gmail.com>wrote:
> true nuf. it appears he used area 0 ONLY however and used default GRE
> tunnel and OSPF values (ospf cost of 11111) so with his endpoint being only
> a couple of hops away, he never should've "preferred" the tunnel for his
> endpoints in the first place with or without the distribute list. I'm
> willing to be he used GNS3 and it's a gliche or something unless there's
> more to his config' that he didnt' post.
>
> Jason
>
>
> On Sun, Jan 11, 2009 at 12:42 PM, Scott Morris <
> smorris@internetworkexpert.com> wrote:
>
>> The rule is that whatever you are using for your destination address needs
>> to NOT be preferred through the tunnel.
>>
>> With that in mind, you look at how you learn the route originally:
>>
>> 1. If via a different protocol, then you can use things like
>> ACL/distribute-lists or even changing the AD (so I don't care if it's
>> learned, it won't get used by routing table)
>>
>> 2. If it's via the same protocol then you need to look differently. Some
>> (RIP, EIGRP) it may simply involve changing the metric. Others (like
>> OSPF)
>> you have further analysis to look at about whether it's the SAME route you
>> are learning (instead of a /24 vs. /32 if loopback) as well as other fun
>> things like intra-area vs. inter-area vs. external route.
>>
>> But once you understand how the router learned/chose the router ORIGINALLY
>> (pre-tunnel) and then understand what is changing the tunnel becomes up...
>> Compare the two and you should be good.
>>
>> Cheers,
>>
>>
>>
>>
>> -----Original Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>> Nitro Drops
>> Sent: Sunday, January 11, 2009 8:27 AM
>> To: ccielab@groupstudy.com
>> Subject: Recursive Routing
>>
>> Hi All,
>>
>> Have been trying to fix my recursive routing for OSPF in the last 2 hours.
>>
>> R1 F0/0 .1 >> 155.1.37.0 >> .2 F0/0 R2 F0/1 .2 >> 155.1.0.0 >> .3 F0/0
>> R3
>>
>> GRE tunnel created between R1 and R3
>>
>> R1
>> interface Tunnel0
>> ip address 155.1.57.1 255.255.255.0
>> tunnel source 155.1.37.1
>> tunnel destination 155.1.0.3
>>
>> router ospf 1
>> network 155.1.0.0 0.0.255.255 area 0
>> distribute-list 2 in Tunnel0
>>
>> access-list 2 deny 155.1.0.0 0.0.0.255
>> access-list 2 deny 155.1.37.0 0.0.0.255
>> access-list 2 permit any
>>
>>
>> R3
>> interface Tunnel0
>> ip address 155.1.57.3 255.255.255.0
>> tunnel source 155.1.0.3
>> tunnel destination 155.1.37.1
>>
>> router ospf 1
>> network 155.1.0.0 0.0.255.255 area 0
>>
>> distribute-list 2 in Tunnel0
>>
>>
>> access-list 2 deny 155.1.0.0 0.0.0.255
>>
>> access-list 2 deny 155.1.37.0 0.0.0.255
>>
>> access-list 2 permit any
>>
>>
>> To prevent recursive routing, i have used a distribute-list to prevent
>> learning the tunnel destination from the tunnel interface. However, my int
>> tunnel keeps on flapping (Debug IP routing as attached), did i missed out
>> anything on my configs or did i use the wrong method? I used the same
>> method
>> on RIP & EIGRP, distribute-list works fine on both of them,
>> distribute-list
>> applying in/out to stop the tunnel destination from advertising/learning
>> from
>> the tunnel interface.
>>
>> Except on OSPF, i can only prevent the router from learning from the
>> tunnel
>> destination, CANT stop advertising the tunnel destination out of the
>> tunnel
>> interface, as the OSPF distribute-list only works for inbound.
>>
>> Cheers
>> Nit
>>
>>
>> IP routing debugging is on
>> R1#
>> *Mar 1 08:54:30.021: %OSPF-5-ADJCHG: Process 1, Nbr 15.2.2.2 on Tunnel0
>> from
>> LOADING to FULL, Loading Done
>> *Mar 1 08:54:41.541: RT: del 155.1.0.0/24 via 155.1.37.2, ospf metric
>> [110/120000]
>> *Mar 1 08:54:41.545: RT: delete subnet route to 155.1.0.0/24
>> *Mar 1 08:54:41.549: RT: NET-RED 155.1.0.0/24
>> *Mar 1 08:54:48.869: %LINEPROTO-5-UPDOWN: Line protocol on Interface
>> Tunnel0,
>> changed state to down
>> *Mar 1 08:54:48.881: RT: is_up: Tunnel0 0 state: 4 sub state: 1 line: 0
>> has_route: True
>> *Mar 1 08:54:48.885: %OSPF-5-ADJCHG: Process 1, Nbr 15.2.2.2 on Tunnel0
>> from
>> FULL to DOWN, Neighbor Down: Interface down or detached
>> *Mar 1 08:54:48.893: RT: interface Tunnel0 removed from routing table
>> *Mar 1 08:54:48.893: RT: del 155.1.57.0/24 via 0.0.0.0, connected metric
>> [0/0]
>> *Mar 1 08:54:48.897: RT: delete subnet route to 155.1.57.0/24
>> *Mar 1 08:54:48.901: RT: NET-RED 155.1.57.0/24
>> *Mar 1 08:54:51.553: RT: SET_LAST_RDB for 155.1.0.0/24
>> NEW rdb: via 155.1.37.2
>>
>> *Mar 1 08:54:51.561: RT: add 155.1.0.0/24 via 155.1.37.2, ospf metric
>> [110/120000]
>> *Mar 1 08:54:51.561: RT: NET-RED 155.1.0.0/24
>> *Mar 1 08:54:57.869: %LINEPROTO-5-UPDOWN: Line protocol on Interface
>> Tunnel0,
>> changed state to up
>> *Mar 1 08:54:57.881: RT: is_up: Tunnel0 1 state: 4 sub state: 1 line: 0
>> has_route: False
>> *Mar 1 08:54:57.885: RT: SET_LAST_RDB for 155.1.57.0/24
>> NEW rdb: is directly connected
>>
>> *Mar 1 08:54:57.889: RT: add 155.1.57.0/24 via 0.0.0.0, connected metric
>> [0/0]
>> *Mar 1 08:54:57.893: RT: NET-RED 155.1.57.0/24
>> *Mar 1 08:54:57.897: RT: interface Tunnel0 added to routing table
>> *Mar 1 08:54:58.973: %OSPF-5-ADJCHG: Process 1, Nbr 15.2.2.2 on Tunnel0
>> from
>> LOADING to FULL, Loading Done
>> *Mar 1 08:55:11.577: RT: del 155.1.0.0/24 via 155.1.37.2, ospf metric
>> [110/120000]
>> *Mar 1 08:55:11.581: RT: delete subnet route to 155.1.0.0/24
>> *Mar 1 08:55:11.585: RT: NET-RED 155.1.0.0/24
>> R1#undebug <http://155.1.0.0/24R1#undebug>
>> *Mar 1 08:55:17.901: %OSPF-5-ADJCHG: Process 1, Nbr 15.2.2.2 on Tunnel0
>> from
>> FULL to DOWN, Neighbor Down: Interface down or detached
>> *Mar 1 08:55:18.869: %LINEPROTO-5-UPDOWN: Line protocol on Interface
>> Tunnel0,
>> changed state to down
>> *Mar 1 08:55:18.877: RT: is_up: Tunnel0 0 state: 4 sub state: 1 line: 0
>> has_route: True
>> *Mar 1 08:55:18.881: RT: interface Tunnel0 removed from routing table
>> *Mar 1 08:55:18.885: RT: del 155.1.57.0/24 via 0.0.0.0, connected metric
>> [0/0]
>> *Mar 1 08:55:18.889: RT: delete subnet route to 155.1.57.0/24
>> *Mar 1 08:55:18.889: RT: NET-RED 155.1.57.0/24
>> R1#undebug <http://155.1.57.0/24R1#undebug> al
>> *Mar 1 08:55:21.589: RT: SET_LAST_RDB for 155.1.0.0/24
>> NEW rdb: via 155.1.37.2
>>
>> *Mar 1 08:55:21.597: RT: add 155.1.0.0/24 via 155.1.37.2, ospf metric
>> [110/120000]
>> *Mar 1 08:55:21.597: RT: NET-RED 155.1.0.0/24l
>> All possible debugging has been turned off
>>
>>
>>
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