OSPF area types question

[jon_panes24]

hi guys,

I am testing different types of OSPF network types.

I have this topology

R1---switch---R2

on R1s link to the switch, i left it on a default of OSPF broadcast mode and on R2 link to the switch I changed it to OSPF point-to-multipoint, i also changed the hello timers on R2 to 10 so it will match hello packets and form neighbors. The neighbors formed a full state, but I get this error when I try to advertise a loopback interface into the ospf process:

%OSPF-4-ERRRCV: Received invalid packet: Bad Checksum from 1.1.1.2, FastEthernet1/0

When I place R2 on broadast mode I receive the route that I am advertising.I was wondering does point-to-multipoint does something to the checksum of the advertised route?

[Vasilii Mikhailovskii]

Hello.

Broadcast and P2MP are not compatible with each other.

Even though you made the routers to exchange LSDB, OSPF would never converge, as R1 became DR (originated network LSA, and state it's connected to transit network), while R2 states (per LSA) been directly connected to R1. As a result, during SPF calculation this inconsistency won't allow the link to be taken into account.

The error message you observed might be due to bad cable or due to some issue on the switch. It has nothing common with OSPF network types.

[eehabsuliman]

%OSPF-4-ERRRCV: Received invalid packet: Bad Checksum from 1.1.1.2, FastEthernet1/0

The router generating this message has received an invalid OSPF packet on FastEthernet1/0 from neighbor 1.1.1.2. The packet is invalid because the OSPF checksum is incorrect. The cause of the bad checksum is difficult to define. Some possible causes of the problem are:

• A device between the neighbors, such as a switch, is corrupting the packet.

• The sending router's packet is invalid. In this case, either the sending router's interface is bad, or the error is caused by a software bug.

• The receiving router is calculating the wrong checksum. In this case, either the receiving router's interface is bad, or the error is caused by a software bug. This is the least likely cause of this error message.

Solution

This problem can be difficult to troubleshoot, but you can start with this solution. Cisco has found that this solution is effective in 90 percent of cases. It is important to complete these steps in order:

1. Change the cable between the routers. In the previous example, this would be the router that sends the bad packet (1.1.1.2) and the router that complains about these bad packets.

2. If the previous step does not fix the problem, use a different port on the switch in between the routers.

3. If the previous step does not fix the problem, connect the routers directly using a crossover cable (whenever physical location allows). If you receive no further messages, the switch is most likely corrupting the packet.

   If none of the above solves the problem, contact the Cisco Technical Support and work with an engineer to look for a bug in the Cisco IOS^® Software, or for a possible Return Material Authorization (RMA) for partial or full parts replacement.