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Ch. 31 Q and A

Ch. 31 Q and A. CS332 Spring 2014. Network management more than just Ethernet .

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Ch. 31 Q and A

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  1. Ch. 31 Q and A CS332 Spring 2014

  2. Network management more than just Ethernet Q: Comer mentions that network managers need to be able to account for different types of networks.  How often is this the case any more? Besides wireless/Ethernet what types of network protocols are still common in industry (excluding ISP's)? A: Network management isn’t just about the hardware (wireless/Ethernet). At Calvin, they have to configure DNS, DHCP, VoIP, VPNs, etc. A lot of this can be done with SNMP.

  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. Self-configuring network devices? Q: Comer notes that it's a challenge to keep every piece of hardware configured consistently. Is there a way to have network devices obtain configuration details from a central resource that knows everything about the network? A: There have been multiple efforts to do such a thing (“Directory-enabled Networks”, is one effort). But, AFAIK, nothing has ever taken hold.

  5. Network Mgmt Tools/Apps Q: Is the main difference between network management tools and applications the fact that the tools run on top of the network while the applications run in the network? A: Each manageable device in the network runs an SNMP agent (routers, switches, PCs, etc.), and the network manager runs an application that polls these devices to make sure they are configured and behaving correctly.

  6. 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)

  7. Codes to communicate? Q: Does SNMP just use codes to communicate, each of which has some meaning? A: Not sure of this question, but… SNMP depends on the MIBs that are defined – common MIBs or vendor-specific MIBs for a device. If you know what kind of device you have, you can know what kind of information you can retrieve from it via SNMP.

  8. MIBs on multiple machines Q: Can the same MIB variable capture two different stats from different machines? A: SNMP can query for the same MIB value on multiple machines, but an SNMP request goes to a single machine at a time. But, you could ask for the print queue on any printer you know about on campus.

  9. SNMP Examples Q: Can you give some examples of uses for SNMP? A: MIBs exist for just about everything you can think of… IP information, interface info, routing table, arp table, processes that are running, load average, uptime, users, …

  10. 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.

  11. 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.

  12. Security? Q: Does SNMP have any considerations for security? A: SNMPv3 has decent security (as I have read). SNMPv1 and v2 were quite bad: you provide a password on the command line and in the packet when you make a query…

  13. 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.)

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