troubleshooting Flashcards
what is bpdu?
A bridge protocol data unit (BPDU) is a data message transmitted across a local area network to detect loops in network topologies.
multicast flooding
no specific host is associated with the multicast Mac add in the cam table
asymmetrical routing
packets leave via one path and return via a different path
–> problem for the stageful firewall
–> put the firewall closer to the system they are protecting (vs. edge)
how to prevent switching/ bridging loop?
enable spanning tree protocol
how to prevent routing loop?
enable split horizon (router cannot advertise a route on the same interface that the message came from)
–> route poisoning (automatically increasing the cost of repetitive route)
–> hold down timer (RIP) ; prevents bad routes from being restored and passed to other routers by accident
DHCP snooping
DHCP Snooping is a security technology on a Layer 2 network switch that can prevent unauthorized DHCP servers from accessing your network.
It is a protection from the untrusted hosts that want to become DHCP servers. DHCP Snooping works as a protection from man-in-the-middle attacks. DHCP itself operates on Layer 3 of the OSI layer while DHCP snooping operates on Layer 2 devices to filter the traffic that is coming from DHCP clients.
it will allow DHCP server messages like DHCPOFFER and DHCPACK that are coming from a trusted source. If the DHCP server messages are coming from untrusted ports, it will discard the DHCP traffic.
A technician added memory to a router, but the router refuses to recognize the new memory module. The router is then powered down, and the technician relocates all of the memory to different modules. On startup, the router does not boot and displays memory errors. Which of the following is the MOST likely cause of this issue?
The most likely cause is that the memory chips are faulty because they have suffered from electrostatic discharge (ESD) during the chips’ installation and movement.
Which of the following network issues can be prevented by configuring the split-horizon options on your network devices?
A split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned.
While troubleshooting, a technician notices that some clients using FTP still work and that pings to the local routers and servers are working. The technician tries to ping all known nodes on the network, and they reply positively, except for one of the servers. The technician notices that ping works only when the hostname is used but not when FQDN is used. What server is MOST likely offline?
The DNS Server translates Fully Qualified Domain Names (FQDN) to IP addresses. Since the technician cannot ping the server using its fully qualified domain name (FQDN), the DNS server is likely offline.
A network technician was tasked to install a network printer and share it with a group of five instructors at Dion Training. The technician plugged the device into a switchport and noticed the link light turned green. Unfortunately, the printer was unable to obtain an IP address automatically. Which of the following is a potential reason for this error?
The DHCP scope is used as a pool of IP addresses that can be assigned automatically. The issue might be that there are no more IP addresses left in the scope, and is therefore exhausted.
Since the scenario specifies that the printer was unable to obtain an IP address automatically, it is most likely a DHCP issue.
It has been determined by network operations that there is a severe bottleneck on its mesh topology network. The field technician has chosen to use log management and found that one router makes routing decisions slower than the others on the network. Which of the following types of issues would you classify this as?
Routing decisions are processed by the router and rely on the networking device’s central processing unit (CPU). The CPU performance can become a severe bottleneck in the network performance if you have an underpowered router for a large enterprise environment.
