Chapter 16 - Configuring IPv4 Addresses and Routes Flashcards
If one LAN-based host wants to send data to another LAN-based host and that destination host is local, what 2 steps does the sending host take?
1) Find the destination host’s MAC address. Use the already known Address Resolution Protocol (ARP) table entry, or use ARP messages to learn the information.
2) Encapsulate the IP packet in a data link frame, with the destination data link address of the destination host.
If one LAN-based host wants to send data to another LAN-based host and that destination host is NOT local, what steps does the sending host take?
1) Find the default gateway’s MAC address. Use the already known ARP table entry, or use ARP messages to learn the information.
2) Encapsulate the IP packet in a data link frame, with the destination data link address of the default gateway.
What’s the 1st step in a router’s routing logic when it receives a data link frame?
To choose whether or not to process the frame. Process it if:
1) The frame has no errors (per the data link trailer Frame Check Sequence, or FCS, field)
2) The frame’s destination data link address is the router’s address (or an appropriate multicast or broadcast address).
If the router chooses to process a frame once it receives it, what are the next steps in a router’s routing logic?
2) De-encapsulate the packet from inside the data link frame.
3) Make a routing decision by comparing the packet’s destination IP address to the routing table and find the route that matches the destination address.
4) Encapsulate the packet into a data link frame appropriate for the outgoing interface. When forwarding out LAN interfaces, use ARP as needed.
5) Transmit the frame out the outgoing interface, as listed in the matched IP route.
Paraphrase the 5 steps of a router’s routing logic.
The router receives the frame, removes the packet from inside the frame, decides where to forward the packet, puts the packet into another frame, and sends the frame.
If a router receives a frame that is not the router’s unicast MAC address for that interface, what does it do with the frame?
The router ignores that frame.
In a routing table, routes for remote subnets typically list what 2 things?
They typically list both an outgoing interface and the next-hop router IP address.
In a routing table, routes for subnets that connect directly to the router list only what?
The outgoing interface.
What does CEF stand for?
Cisco Express Forwarding
Routers can add routes to their routing tables through what 3 different methods?
1) Connected routes
2) Static routes
3) Routing protocols
What are connected routes in a routing table?
These routes are added because of the configuration of the ip address interface sub-command on the local router.
What are static routes in a routing table?
These routes are added because of the configuration of the ip route global command on the local router.
What are routes added by routing protocols?
Added as a function by configuration on all routers, resulting in a process by which routers dynamically tell each other about the network so that they all learn routes.
A Cisco router automatically adds a route to its routing table for the subnet connected to each interface, assuming that what two facts are true?
1) The interface is in a working state
2) The interface has an IP address assigned through the ip address interface subcommand
What are 3 options for connecting a router to each subnet on a VLAN?
1) Use a router, with one router LAN interface and cable connected to the switch for each and every VLAN (typically not used).
2) Use a router, with a VLAN trunk connecting to a LAN switch.
3) Use a Layer 3 switch.
