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How to interpret the option bits in the output of the show ip ospf neighbor command?

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TitleHow to interpret the option bits in the output of the show ip ospf neighbor command?

Products: NetIron MLX, XMR, CES, CER, BigIron RX

All software versions

IPRouting Protocols - OSPF

The command show ip ospf neighbor has an options field in the output; this field is related to the options in the OSPFhello packet. For example:

show ip ospf neighbor
Number of Neighbors is 2, in FULL state 2

Port Address Pri State Neigh Address Neigh ID Ev Opt Cnt
1/1 1 FULL/BDR 6 66 0
1/2 1 FULL/DR 5 66 0


To interpret the options field in theshow ip ospf neighborcommand output,users mustdo the following:
1. Take the value in output fromthe example given above, whichis 66.
2. Convert the decimal number displayed in the outputto binary. In this example, it would be the following:

66 =100 0010

3. Take the bits in the binary output and match them against the positions in the OSPF Options Field, which is defined as follows:
Note:1 in the binary output indicates that the bit is set:

| * | O | DC | EA | N/P | MC | E | * |
10 0 00 1

Thus, in this particular case, with options = 66, the E and O bits are set. The bits in the OSPF Options Field are defined as follows:

E-bit - Support for Type-5 AS-External-LSAs (ExternalRoutingCapability)
MC-bit -Support for Multicast extensions to OSPF (MOSPF)
N/P-bit - Support for handling Type-7 LSAs (NSSA)
EA-bit - Support for External-Attributes-LSAs
DC-bit - Support for demand circuits
O-bit - Support for Opaque-LSAs

Additional notes



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