18 - IP Services III - Miscellaneous Flashcards
What are First Hop Redundancy Protocols?
Protocols that allow hosts to best take advantage of of redundant routers in a subnet e.g. as default routers
What are the 3 FHRP options?
- HSRP
- VRRP
- GLBP
What is VRRP?
Virtual Router Redundancy Protocol
Approach: active/standby
Load balancing per subnet
What is GLBP?
Gateway Load Balancing Protocol
Approach: active/active
Load balancing per host
What model does HSRP operate under?
Active/Standby
Only ever one router a time actively supporting end user traffic, while other routes wait in standby state ready to take over if the active router encounters a problem
What would the MAC address entry be on a host for the currently active HSRP Routers virtual IP?
The virtual MAC of the active Router
How do switches change their MAC table entries for the HSRP Virtual MAC?
The new active router sends an Ethernet frame with a gratuitous ARP containing the VMAC entry but with ports that point towards R2
How could you do some load balancing with HSRP?
- One router active for a given VLAN, then another for a different one
- HSRP Groups
Where are are FHRPs needed?
Any device that acts as a default router
What is SNMP?
Application layer protocol for communication between managers and agents, where agents are devices on the network maintaining databases of information about themselves (config, status, counters, etc)
What is an SNMP Manager?
Network management app running on a server (NMS)
What is a NMS?
Network Management Station
Device that hosts an SNMP Manager
What is an SNMP Agent?
Software running inside each device (router, switch, etc) that maintains a database of information about that device
How does the SNMP Manager / NMS retrieve information from the Agents?
It polls them using SNMP get messages to retrieve information from their MIBs
- SNMP Get
- SNMP GetNext
- SNMP GetBulk
What is an MIB?
SNMP Agents Management Information Base
Collection of information organized hierarchically
How can the NMS change configurations on an agent?
Sending SNMP Set messages
How can SNMP Agents initiate communications to the NMS?
Using notifications messages such as SNMP Trap and Inform.
SNMP Agents can use Trap or Inform messages to list the state of certain MIB variables when those variables reach a certain state e.g. this interface is down
How are SNMP Trap and Inform messages different?
Traps
- Fire and forget
- UDP, no guarantee of delivery or error recovery
Inform
- SNMPv2 and up
- UDP but add application layer reliability
- NMS must acknowledge receipt with SNMP Response message
What is an OID?
ObjectID that defines each variable in the MIB
What is Cisco Prime?
NMS Application (SNMP Manager)
What is the IFS?
IO File System
What two entries typically denote physical storage on routers?
disk
usbflash
True/False: Routers can boot IOS from USB flash drives
False
What commands could you use to show flash memory content?
show flash
dir flash0:
