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OSPF routing confusion/loop?

 
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pattap
Regular Advisor

OSPF routing confusion/loop?

Hi all

I have noticed strange behaviour between two switches participating in ospf, little diagram below. A and B are connected via ospf network type p2phpe forum2.png

what I can't understand is why switch a a still learns 10.3.0.0 range from router b even though they are all directly connected to it

HP-a dis ip routing table 10.3.0.0
Summary Count : 1

Destination/Mask    Proto  Pre  Cost         NextHop         Interface
10.3.0.0/16         OSPF   150  1            10.10.10.b          Vlan10

when checking for IP RT more specifically for one of the 10.3 addresses:

 

HP-a dis ip routing-table 10.3.2.0

Summary Count : 3

Destination/Mask    Proto  Pre  Cost         NextHop         Interface
10.3.0.0/16         OSPF   150  1            10.10.10.b       Vlan10
10.3.2.0/24         Direct 0    0            10.3.2.1         Vlan100
10.3.2.0/32         Direct 0    0            10.3.2.1         Vlan100

they way this was discovered was quite coincidental by mistyping IP address while performing tracert, ip used didn't exist on the network and the result was that it would bounce between switch a and b until it hit 30 hops, so it looked something like this

 

Tracing route to 10.3.20.10 over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  10.x.x.1
  2     *        *        *     Request timed out.
  3    <1 ms    <1 ms    <1 ms  10.x.x.x
  4     1 ms     1 ms     1 ms  10.10.10.a
  5    <1 ms    <1 ms    <1 ms  10.10.10.b
  6     1 ms     1 ms     1 ms  10.10.10.a
  7    <1 ms    <1 ms    <1 ms  10.10.10.b
  8     1 ms     1 ms     1 ms  10.10.10.a
  9    <1 ms    <1 ms    <1 ms  10.10.10.b
 10     1 ms     1 ms     1 ms  10.10.10.a
 11    <1 ms    <1 ms    <1 ms  10.10.10.b
 12     1 ms     1 ms     1 ms  10.10.10.a
 13    <1 ms    <1 ms    <1 ms  10.10.10.b
 14     1 ms     1 ms     1 ms  10.10.10.a
 15    <1 ms    <1 ms    <1 ms  10.10.10.b
 16     1 ms     2 ms     1 ms  10.10.10.a
 17    <1 ms    <1 ms    <1 ms  10.10.10.b
 18     1 ms     1 ms     1 ms  10.10.10.a
 19    <1 ms    <1 ms    <1 ms  10.10.10.b
 20     1 ms     1 ms     1 ms  10.10.10.a
 21    <1 ms    <1 ms    <1 ms  10.10.10.b
 22     1 ms     1 ms     1 ms  10.10.10.a
 23    <1 ms    <1 ms    <1 ms  10.10.10.b
 24     1 ms     1 ms     1 ms  10.10.10.a
 25    <1 ms    <1 ms    <1 ms  10.10.10.b
 26     1 ms     1 ms     1 ms  10.10.10.a
 27     1 ms    <1 ms    <1 ms  10.10.10.b
 28     1 ms     1 ms     1 ms  10.10.10.a
 29     1 ms    <1 ms    <1 ms  10.10.10.b
 30     1 ms     1 ms     1 ms  10.10.10.a