The IP objects are the statistics and gateway routing tables for the IP layer. The "(G) after "IP" indicates that graphs are available. The graphs consist of several scalars and four tables. They track the datagram information in terms of datagrams forwarded, discarded due to format errors, discarded due to misdelivery, discarded due to resource limitations and so forth. The IP Routing table is part of this group and its contents are discussed separately.
The initial IP MIB information is available upon clicking Get MIB with the MIB type set to IP. The route table is actually a part of the IP MIB and may be viewed by selecting the Route Table MIB Type.
Figure 60. SNMP Browser: IP MIB Information
The fields on the IP MIB Information screen are:
Forwarding |
Indicates whether this entity is acting as an IP gateway in respect to the forwarding of datagrams received by, but not addressed to, this entity. IP gateways forward datagrams. IP hosts do not (except those source-routed via the host). The options are: 1 = forwarding (acting as a gateway), 2 = not forwarding (not acting as a gateway). |
Default TTL |
The default value inserted into the Time-To-Live (TTL) field of the IP header of datagrams originated at this entity, whenever a TTL value is not supplied by the transport layer protocol. The values may be 1-255. |
Reassembly Timeout |
The maximum number of seconds that received fragments are held while awaiting reassembly at this entity. |
Receives In |
The total number of input datagrams received from interfaces, including those received in error. |
Requests Out |
The total number of IP datagrams, which local IP user-protocols (including ICMP), supplied to IP in requests for transmission. Note that this counter does not include any datagrams counted in ipForwDatagrams. |
Forward Datagrams In |
The number of input datagrams for which this entity was not their final IP destination, as a result of which an attempt was made to find a route to forward them to that final destination. In entities that do not act as IP Gateways, this counter includes only those packets, which were source-routed via this entity, and the source-route option processing was successful. |
Delivers In |
The total number of input datagrams successfully delivered to IP user-protocols (including ICMP). |
Header Errors In |
The number of input datagrams discarded due to errors in their IP headers, including bad checksums, version number mismatch, other format errors, time-to-live exceeded, errors discovered in processing their IP options, etc. |
Address Errors In |
The number of input datagrams discarded because the IP address in their IP header's destination field was not a valid address to be received at this entity. This count includes invalid addresses (e.g., 0.0.0.0) and addresses of unsupported Classes (e.g., Class E). For entities that are not IP gateways and therefore do not forward datagrams, this counter includes datagrams discarded because the destination address was not a local address. |
Unknown Protocols In |
The number of locally addressed datagrams received successfully but discarded because of an unknown or unsupported protocol. |
No Routes Out |
The number of IP datagrams discarded because no route could be found to transmit them to their destination. This counter includes any packets counted in ipForwDatagrams that meet this "no-route" criterion, including any datagrams that a host cannot route because all its default gateways are down. |
Discards In |
The number of input IP datagrams for which no problems were encountered to prevent their continued processing, but which were discarded (e.g., for lack of buffer space). This counter does not include any datagrams discarded while awaiting reassembly. |
Discards Out |
The number of output IP datagrams for which no problem was encountered to prevent their transmission to their destination, but they were discarded (e.g., for lack of buffer space). Note that this counter includes datagrams counted in ipForwDatagrams if any such packets meet this discretionary discard criterion. |
Reassembly Required |
The number of IP fragments received that needed to be reassembled at this entity. |
Fragment Created |
The number of IP datagram fragments generated as a result of fragmentation at this entity. |
Reassembly OK |
The number of IP datagrams successfully reassembled. |
Reassembly Failed |
The number of failures detected by the IP re-assembly algorithm (for whatever reason: timed out, errors, etc.). Note that this is not necessarily a count of discarded IP fragments because some algorithms (notably the algorithm in RFC 815) can lose track of the number of fragments by combining them as they are received. |
Fragment OK |
The number of IP datagrams that have been successfully fragmented at this entity. |
Fragment Failed |
The number of IP datagrams that have been discarded because they needed to be fragmented at this entity but could not be, e.g., because their Don't Fragment flag was set. |