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Ch. 31 Q and A

Ch. 31 Q and A. IS 333 Spring 2014. FCAPS. Q: In the working world how is the responsibility of the FCAPS shared? Is one person's job or does this depend on the size of the organization?

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Ch. 31 Q and A

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  1. Ch. 31 Q and A IS 333 Spring 2014

  2. FCAPS Q: In the working world how is the responsibility of the FCAPS shared? Is one person's job or does this depend on the size of the organization? A: AFAIK, the jobs are distributed. A team in the NOC (Network operations center) handles errors (“faults”). Another team is responsible for provisioning/configuration – because they are dealing with customer requests, etc. Accounting and billing are a totally different department.

  3. SNMP: what layer? Q: What layer does SNMP live at? A: Layer 5. It is carried over UDP typically, ports 161 and 162. Q: Will SNMP work with IPv6? A: Yes, no problems.

  4. SNMP Packet Format Q: What does an SNMP packet look like? A: 1 byte PDU type (get/set/get-next/trap) request id error status error index repeat: (object-id, type, len, value)

  5. Controlling devices Q: How is SNMP used to control a device exactly? It uses the fetch and store paradigm and it talks about resetting a counter, but what about other operations? A: Most of the time SNMP is used for monitoring – getting the status of devices (routers, switches, network file servers, etc.). When stuff is configured, SNMP sets are done to write the correct values to the MIBs on the devices. E.g., you could change the default route on all routers with a set of SNMP set requests. Or clear all ARP caches.

  6. SNMP, MIBs, and ASN.1 • SNMP defines the protocol used to send requests and get responses. • MIBs are defined for common stuff on machines: interfaces, IP statistics, routing tables, ARP tables; and for device-specific values and tables. • ASN.1 is how the values and table entries are encoded in requests and responses.

  7. ASN.1 Q: How does ASN.1 work? A: ASN.1 is an encoding standard. It defines how you encode data for different types: how to send an integer, a string, a bit string, an object-id, a real number, a null, etc. It also tries to minimize the space it takes to encode things. As a result, it is barf-making. A truly evil thing. (As a result, when you build the SNMP data part, you build it backwards in memory, and then reverse-copy it into the packet memory to be sent.)

  8. Why ASN.1? Q: Why exactly does SNMP use ASN.1 encoding? A: Because it is general and was there… Or because some group was feeling nasty and decided that misery loves company… Or maybe it was an April Fool’s joke that “went viral”…

  9. How/where are values stored? Q: In the fetch-store paradigms used for SNMP, how and where are the values stored in a device? A: They are stored somewhere on the device in memory – in the device drivers or OS somewhere. We stored our data in the OS and then queries to values retrieved them out of the OS, and formatted them to be returned.

  10. MIB discovery Q: How can you discover all of the valid fields in the MIB for a given device? A: 1. You read the MIB – or use a management app that has them built in. 2. You use the app to “walk” the MIB tree on the device, using repeated get-next requests. This is how you discover all the interfaces on a machine, e.g., or if the machine will report its ARP table.

  11. SNMP Traps • SNMP also has something called “Traps” or “Alerts” • A machine for network management configures managed devices to send errors to it when they happen. The net mgmt application displays/summarizes them so that a network manager can see when something really bad happens. The manager then has to find the root cause.

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