routing Flashcards
router purpose
transfer packets from one network to another in a way that makes progress toward its end destination.
routing table
Contains one entry for each possible destination network & specifies the next router (neighbor) to forward a packet.
What happens when a packet arrives at a router?
The router will check the routing table & forward the packet to the appropriate neighbor.
What is contained in a routing table (columns)?
One entry for each destination network: network address, network mask to be applied, IP addr of next hop router, specific interface, and some routing computation related metrics.
A router typically has ____ entries in its table
300-400 thousand
Sources of routing information
Directly connected routes, static routes (manually configured), dynamic routing protocols (learned through exchange of information between routers).
Difference between routing & routed protocol
Routing - advertises route info between routers. Routed - protocol with an addressing scheme that defines different network addresses.
2 fundamental approaches to receiving, advertising, and storing routing info
Distance vector & link state
Distance vector
sends full copy of routing table to its directly connected neighbors. May cause routing loops
Link state
routers do not exchange full routing tables. routers send link-state advertisements to advertise the networks they know how to reach.
Techniques used to remove routing loops
split horizon & poison reverse
split horizon
prevents a route learned on one interface from being advertised back out of that same interface
poison reverse
causes a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite
administrative distance
Believability of route - more than one routing protocol may be used by a network. Admin distance is how we decide which protocols are more reliable
Administrative distance of directly connected network
0
Administrative distance of statically configured network
1
Administrative distance of EIGRP
90
Administrative distance of OSPF
110
Administrative distance of RIP
120
Administrative distance of external EIGRP
170
Administrative distance of unknown
255
Metrics for choosing paths to reach another network
Hop count, bandwidth, reliability, delay, etc
Interior vs exterior gateway
Interior operates within an autonomous system, exterior operates between autonomous systems
What does NAT (network address translation) do?
Translates private IP addr (which are not routable on the internet) with public IP addresses (which are routable).
Address translation types
Dynamic NAT, static NAT, port address translation (PAT)
DNAT
IP addresses automatically assigned from a pool. One-to-one translations
SNAT
IP addr manually assigned. One-to-one translations
PAT
Multiple private IP addresses share one public IP. Many-to-one translation
Multicast routing protocols
Internet Group Management Protocol (IGMP) & Protocol Independent Multicast (PIM)
IGMP
Used by clients when they want to join a multicast group
PIM
Based on routing. Routes multicast traffic between multicast-enabled routers
PIM modes of operation
PIM dense mode (PIM-DM) and PIM sparse mode (PIM-SM)
PIM-DM
uses a periodic floor & prune behavior to form an optimal distribution tree. Rarely used
PIM-SM
initially uses a shared distribution tree but eventually creates an optimal distribution tree through SPT (shortest path tree) crossover
ICMP
internet control message protocol - a protocol that devices within a network use to communicate problems with data transmission
