two default-routes installed via ospf

Unanswered Question
Mar 25th, 2012

HI,

     I just want to ask if its ok to have to default routes with the metric installed on a router. IM having this results whenever i tried to trace a route. My ping results are successfull. just wondering if i'll encounter any problems by doing this. Thanks in advance.

R6#
*Mar  1 00:05:00.623: %SYS-5-CONFIG_I: Configured from console by console
R6#sh ip rou
R6#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is 192.168.5.6 to network 0.0.0.0

     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, Loopback1
     2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Loopback2
     192.168.5.0/30 is subnetted, 2 subnets
C       192.168.5.4 is directly connected, FastEthernet0/1
C       192.168.5.0 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 192.168.5.6, 00:04:20, FastEthernet0/1
               [110/1] via 192.168.5.1, 00:00:15, FastEthernet0/0
R6#tra
R6#traceroute 3.3.3.3

Type escape sequence to abort.
Tracing the route to 3.3.3.3

  1 192.168.5.6 40 msec
    192.168.5.1 52 msec
    192.168.5.6 36 msec
  2 192.168.1.1 48 msec
    192.168.1.2 52 msec
    192.168.1.1 36 msec
  3 192.168.4.6 60 msec
    192.168.4.2 64 msec
    192.168.4.6 48 msec
R6#

   

R7#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is 192.168.4.5 to network 0.0.0.0

     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, Loopback3
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback4
     192.168.4.0/30 is subnetted, 2 subnets
C       192.168.4.4 is directly connected, FastEthernet0/1
C       192.168.4.0 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 192.168.4.5, 00:00:48, FastEthernet0/1
               [110/1] via 192.168.4.1, 00:00:48, FastEthernet0/0
R7#tr
R7#traceroute 1.1.1.1

Type escape sequence to abort.
Tracing the route to 1.1.1.1

  1 192.168.4.5 40 msec
    192.168.4.1 52 msec
    192.168.4.5 44 msec
  2 192.168.1.3 24 msec
    192.168.1.4 52 msec
    192.168.1.3 60 msec
  3 192.168.5.5 60 msec
    192.168.5.2 56 msec

     192.168.5.5 60 msec

regards,

I have this problem too.
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patrick.preuss Mon, 03/26/2012 - 00:13

Hi

yes shure can this be ok, but this depends on you topology and if you whant to have it:-)

Your router knows, 0.0.0.0 can be reached via .5 and .1 so you will have load sharing and failover, from my point of view cool i want to have this.

Any way: 

Your view is caused by due to redistributing the default route as an E2 Route.

Is this the correct type? E2s dont know about internal topology, may be E1 is better.

If you think this is not what you whant please review your ospf design (areas, asbr, abr, redistribution).

HTH

Patrick

n.cacatian Mon, 03/26/2012 - 00:20

Hi Patrick,

     The routes came from BGP. I only want default routes going out of the network. BTW, is it normal to have that kind of output when it comes to my traceroute? it seems like the route is bouncing from one route to another before forwarding the traffic outside. will it have any effect on the throughput of my traffic?

regards,

patrick.preuss Mon, 03/26/2012 - 00:31

Hi

yes your packets are bouncing, this is cause be the E2 every router know the route with the same cost and your

router thinks it can reach 0/0 via .1 and via .5 eqal.

This can and will lead to performace problems.

Please review your area design and the redistribution. When possible setup a diffent area for the exit not 0.0.0.0 (backbone) and change the route type to E1.

External E1 takes the actual costs in the areas in consideration, where E2 does not.

HTH

Marwan ALshawi Wed, 03/28/2012 - 04:27

hi there

in brief this depends on what you want

if you leave it like this this router will perform per flow loadbalncing using CEF to chose the exit interface from those installed in the routing table for the default route

if you do not want to do loadbalncing then in the routers that generating the default route you can make one interface in a totaly NSSA where the default route will be LSA type 3 and will be preferred of the E2 one

but you might need to have some sort of conditional defaulte route with a route map so this router will not advertise the default route if its ISP link is down for example

see the bellow links might help you

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a74.shtml

http://packetlife.net/blog/2008/dec/12/ospf-conditional-default-route-injection/

hope this help

if helpful rate

rustom.cisco Wed, 03/28/2012 - 03:44

Hi Neri,

Please do post a rough diagram of the network so that i can get a better idea.

Thanks

Rustom Billimoria

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Posted March 25, 2012 at 11:56 PM
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