Routing Flashcards
Purpose of a router
Route traffic between networks or subnets
Layer 3 devices that separate broadcast domains
How routers make routing decisions
Layer 3 to Layer 2 mapping
Routers use ARP caches to map an IP address to a given MAC address
Routing tables
Table kept by router to determine which route entry is best fit for the network
Route entry with longest prefix is the most specific network
Sources of routing information
Directly connected routes - physical connection
Static routes - configured by admin
Dynamic routing protocols - learned
Split Horizon
Prevents a route learned on one interface from being advertised back out the 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
IGP
Interior Gateway Protocol
Operates within autonomous system (routing)
EGP
Exterior Gateway Protocol
Operates between autonomous systems (routing)
Router Advertisement Method
Distance Vector
Link State
Distance Vector
Sends full copy of routing table to its directly connected neighbors at regular intervals
Slow - all routers must update their tables
Uses hop count as metric
Link State
Requires all routers to know paths of all other routers in the network
OSPF or IS-IS
Faster than Distance Vector
Uses cost as metric
RIP
Routing Information Protocol Interior Gateway Protocol (IGP) Distance Vector protocol using hop count Maximum hops of 15 Updates every 30sec Old protocol
OSPF
Open Shortest Path First
Interior Gateway Protocol (IGP)
Link State protocol using cost
Cost based on link speed between routers
IS-IS
Intermediate System to Intermediate System
Interior Gateway Protocol (IGP)
Link State protocol using cost
Similar to OSPF but not as popular
EIGRP
Enhanced Interior Gateway Routing Protocol Interior Gateway Protocol (IGP) Hybrid of distance vector and link state Uses bandwidth and delay Cisco only
BGP
Border Gateway Protocol
External Gateway Protocol (EGP)
Path vector using number of autonomous system hops instead of router hops
Backbone of internet
Router AD
Administrative Distance
Index of believability
Lower AD = more believable
AD metrics
Directly connected network - 0 Statically configured network - 1 EIGRP - 90 OSPF - 110 RIP - 120 External EIGRP - 170 Unknown - 255 (unreachable)
Route Redistribution
Network to support more than one routing protocol
Router can translate routing protocols between ports
NAT
Network Address Translation
Translates private IP addresses to public IP addresses over public networks
Conserves limited number of IPv4 addresses
PAT
Port Address Translation
Utilizes port numbers instead of IP addresses for translation
Multiple private IP addresses share one public IP
Small networks
DNAT
Dynamic NAT
IP addresses automatically assigned from pool
Many-to-many translations
SNAT
Static NAT
IP addresses manually assigned
One-to-one translations
NAT Inside Local
Private IP referencing inside device
