6.4 IPv4 Routing Overview Flashcards
What layer of the OSI model does ping work on
Network layer
How does ping work exactly
by sending an ICMP echo request packet to a remote host. The source address of the echo request packet is the IP address of the interface from which the packet is sent. An echo reply response from the target device verifies that the host can communicate with the destination.
When you use ping what is the output
reports success or failure, together with round-trip statistics
What does a successful ping test result to
A successful ping test verifies Network layer connectivity between devices as well as the TCP/IP configuration of all devices in the path.
What is an advantage of the ping command
it allows you to test communication near the source of the problem.
What level in the CISCO CLI does the extended ping command work on
Only the privileged exec command cli
How does the traceroute command work in CISCO CLI
traceroute sends successive ICMP messages to an unreachable port address at a remote host.
While using the traceroute command what does a time exceeded error indicate?
A time exceeded error indicates that a server along the route has seen the packet and discarded it.
Describe IP configuration errors
Not having the IP address, the subnet mask, DNS server addresses, or the default gateway address set correctly on your network host will interfere with communication with the default gateway router. You can check the configuration of your network host using the ipconfig command on a Windows system or the ifconfig command on a Linux machine.
Describe mismatched subnet masks
The subnet masks on the router should line up with the subnet mask on the host. If the IP address used by the PC is not on the same subnet as the router interface, outbound traffic will work fine, but inbound traffic from the router to the workstation will not work.
Describe DNS configuration errors
If a network host is configured with the wrong IP address for the DNS server, any network process that requires name resolution will fail. Just like hosts, the router can be configured with the IP addresses of several DNS servers so it can resolve hostnames into IP addresses. Just as with network hosts, name resolution will fail if the router is configured with the wrong DNS server address.
Describe DHCP relay issues
DHCP relay issues occur when the DHCP server is on a different network segment than the system trying to obtain an address. To get around this issue, you can configure the router with a helper IP address.
Describe LAN interface issues
An unplugged network cable A defective network cable A shutdown interface A speed mismatch An administrative shutdown The protocol status is in err-disabled mode because of port security settings
Describe Overlapping routes
This occurs where a destination address in a packet that the router receives matches more than one of the routes that are within that router’s routing table. This could be caused by poor network design, route summarization, or incorrect static routes.
Describe ACL issues
If access control lists (ACLs) are not configured correctly, they can impact legitimate traffic that should be passing between routers. If you suspect ACLs are incorrectly limiting traffic between routers, there are a couple of things you can keep in mind. First of all, remember that the first rule in the ACL that matches a packet will be the rule that’s applied to that packet.
Any remaining rules in the ACL will not be applied to that packet. They will be ignored. Also, remember that the last rule in an ACL is an implicit deny. If none of the rules you’ve configured in the ACL match a given packet, then that packet is going to be dropped by default. Also, ACLs are bidirectional. You must determine which rules are applied in which direction.
