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NE5000E Receives Two LSAs with the Same LSID, But One of Them Cannot Calculate the Route.

Publication Date:  2012-07-27 Views:  100 Downloads:  0
Issue Description
 For the network diagram, see the appendix.
The traffic to the BAS is uneven. Therefore, the route from NE5000E-1 to the destination network segment under the BAS adopts "NE5000E-1―BAS―destination" or "NE5000E-1―NE5000E-2―BAS―destination" to form load balancing traffic.
In the following example, the test network segment is from NE5000E-1 to the destination network segment (58.53.80.0).
The user specifies a static route to 58.53.80.0 on NE5000E-2 and imports static to OSPF. NE500E-1 receives the ASE LSA whose LS ID is 58.53.80.0 from both NE5000E-2 and BAS.
The LSA from BAS takes effect and calculates the route, but the LSA from NE5000E-2 does not calculate the route.
<NE5000E>disp ospf lsdb ase 58.53.80.0

OSPF Process 1 with Router ID 58.53.53.23
Link State Database


Type : External
Ls id : 58.53.80.0
Adv rtr : 58.53.53.21
Ls age : 1327
Len : 36
Options : DC
seq# : 80000037
chksum : 0x3fc3
Net mask : 255.255.255.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 0.0.0.0
Tag : 1

Type : External
Ls id : 58.53.80.0
Adv rtr : 58.53.53.1
Ls age : 1157
Len : 36
Options : E
seq# : 80000001
chksum : 0x2288
Net mask : 255.255.255.0
TOS 0 Metric: 1
E type : 2
Forwarding Address : 58.53.55.26
Tag : 1

<NE5000E>disp ip routing-table 58.53.53.21
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1

Destination/Mask Proto Pre Cost Flags NextHop Interface

58.53.53.21/32 O_ASE 150 1 D 58.53.55.22 GigabitEthernet10/0/2 
 
Alarm Information
 Null 
Handling Process
 1. Check the configuration and find that the configuration is OK.
2. Check that the LSA with the FA setting meets route calculation conditions.
<NE5000E>ping 58.53.53.1
PING 58.53.53.1: 56 data bytes, press CTRL_C to break
Reply from 58.53.53.1: bytes=56 Sequence=1 ttl=255 time=1 ms
Reply from 58.53.53.1: bytes=56 Sequence=2 ttl=255 time=1 ms
Reply from 58.53.53.1: bytes=56 Sequence=3 ttl=255 time=1 ms
Reply from 58.53.53.1: bytes=56 Sequence=4 ttl=255 time=1 ms
Reply from 58.53.53.1: bytes=56 Sequence=5 ttl=255 time=1 ms

--- 58.53.53.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/1/1 ms


<NE5000E>disp ip routing-table 58.53.53.1
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 2

Destination/Mask Proto Pre Cost Flags NextHop Interface

58.53.53.1/32 O_ASE 150 1 D 58.53.55.45 GigabitEthernet10
/0/5
O_ASE 150 1 D 58.53.55.49 GigabitEthernet10
/0/6

<NE5000E>ping 58.53.55.26

Reply from 58.53.55.26: bytes=56 Sequence=1 ttl=254 time=1 ms
Reply from 58.53.55.26: bytes=56 Sequence=2 ttl=254 time=1 ms

0.00% packet loss
round-trip min/avg/max = 1/1/1 ms


<NE5000E>disp ip routing-table 58.53.55.26


58.53.55.24/30 OSPF 10 101 D 58.53.55.45 GigabitEthernet10
/0/5
OSPF 10 101 D 58.53.55.49 GigabitEthernet10
/0/6
3. On the network, the values of cost for LSAs are 1. Then compare the value of cost for ASBR and that for FA.
For the ASE LSA of type 2, OSPF calculates equivalent routes according to the following comparison principles:
1. Compare the values of cost for LSAs. If the values are the same, go to the next step.
2. Compare the value of cost to the ASBR and that to the FA. If they are the same, equivalent routes are formed.
The value of cost to the FA is found to be 101.
For the LSA with the FA of 0, the value of cost to the ASBR (58.53.53.21) is 1.
For the LSA with non-zero FA, the value of cost to the FA (58.53.53.26) is 101.
The LSAs with the FA setting has lower priority and are not calculated. Therefore, equivalent routes cannot be formed.
The method for forming equivalent routes on this network is as follows:
On the BAS, enable the next hop of the corresponding route to 58.53.80.0 to OSPF and set the interface cost to 100 to enable the issue of an LSA with FA on the BAS (FA is the interface address).
In this manner, on NE5000E-1, the two LSAs have the same features: Both of them have FA and the value of cost to the FA is 101. Therefore, equivalent routes are formed. 
 
Root Cause
 
1. Configuration problem.
2. Forwarding Address in the LSA sent by NE5000E-2 is set to 58.53.55.26. Maybe that is the reason why the LSA is not calculated.
3. The conditions for generating the load balancing route are not available. 
Suggestions
 Null 

END