Routing Flashcards
Split Horizon
Prevents a route learned on one interface from being advertised back out of that same interface (router)
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
Distance Vector routing
Sends full copy of routing table to its directly-connected neighbors at regular intervals
Convergence
Time it takes for routers to update their routing tables in response to a topology change
Hold-down Timer
Prevents updates for a specific period of time and speeds up convergence (routing)
Link State routing
Requires all routers to know about the paths that all other routers can reach in the network
Routing Information Protocol (RIP)
-Distance vector
-Interior
-Uses hop count (maximum hops of 15; 16 is infinite)
-Easy to configure
-updates every 30 seconds
Open Shortest Path First (OSPF)
-Link state protocol
-Interior
-Uses cost(link speed)
Intermediate System to Intermediate System (IS-IS)
-Link state protocol
-Interior
-Uses cost (link speed)
-Functions like OSPF protocol, but not as popular.
Border Gateway Protocol (BGP)
-Distance vector protocol
Sole Exterior
-Uses the number of autonomous system hops instead of router hops
*Only exterior protocol on exam
Route Believability
If a route has a lower administrative distance (AD), the route is more believable
Relevant routing info source in order of Believability
- Direct
- Static
- EIGRP
- OSPF
- RIP
- External EIGRP
Directly connected route
Learned by physical connection between routers
Static Route
Route configured by sys admin
Explain First-Hop Redundancy
Uses Hot Standby Router Protocol (HSRP) to create virtual IP and MAC addresses to provide active and standby routers.
Name 4 First-Hop Redundancy protocols
Hot Standby Router Protocol (HSRP)
Virtual Router Redundancy Protocol (VRRP)
Gateway Load Balancing Protocol (GLBP)
Common Address Redundancy Protocol (CARP)
Default Route
Route that takes effect when no other route is available for an IP destination address
Hot Standby Router Protocol (HSRP)
- Cisco’s proprietary first-hop redundancy protocol which
- An active and a standby router used together
- Establish a fault-tolerant default gateway
- Presents as a asingle router
Virtual Router Redundancy Protocol (VRRP)
- IETF’s open standard variant of HSRP
- Allows for an active router and multiple standby routers
- Open standard
- Simple and automatic election scheme
Multi Router Traffic Grapher (MRTG)
- Creates graphs showing traffic flows through the network interfaces of routers and switches
- Using SNMP
Start Configuration
Stored in NVRAM and contains the commands needed to initially configure a router
Running Configuration
Actively being used by the router at that moment
Asymmetrical Routing
Packet leavs via on path and return via a different path causing issues with dropped packet flows
Missing Routes
When a router cannot reach a destination because there is a missing route in the routing table
Normally fixed by configuring Spanning Tree Protocol (STP)
Switching/Bridge Loop
Occurs whenever there is more than one path between the source and destination devices
Normally fixed by configuring Spanning Tree Protocol (STP)
Routing Loop
Formed when an error occurs in the operation of the routing algorithm and creates a circular route amongst a group of network devices
Route Poisoning
Increasing a router’s metric to an infinitely high number after detecting on of its connected routes has failed
Hold-Down Timer
Prevents bad routes from being restored and passed to other routers by accident
Protocol Independent Multicast Dense Mode (PIM-DM)
- Uses periodic flood and prune behavior to form optimal distribution tree
- Negative performance impact
Protocol Independent Multicast Sparse Mode (PIM-SM)
- Uses a shared distribution tree initially
- Over time creates an optimal distribution tree through shortest path tree (SPT) switchover
Explain Spanning Tree Protocol
Permits redundant links between switches and prevents looping of network traffic
Shortes Path Bridging (SPB)
Used instead of STP for larger network environments.
Enhanced Interior Gateway Routing Protocol (EIGRP)
-Advanced distance vector (Hybrid)
-Interior
-Uses bandwidth and delay
-Cisco only
Router loopback is only on during diagnostic mode
IP Helper
- Enable a single DHCP server to provide IPs to every PC on the network, regardless of whether they are on the same broadcast domain or not.
- Configured on a routed interface such as a VLAN or routers Ethernet interface &
- Adding an IP Helper address to the new interface on the router will allow the DHCP broadcast requests to be forwarded to the workstations
Asymmetric Routing
- Network packets leave via one path and return via a different path
- Cause issues with dropped packet flows by security devices like firewalls and UTM
ASN (Autonomous System Number)
- Used to control routing with BGP
- Control routing within their networks
- Exchange routing information with other ISPs.
- There are 2-byte and 4-byte variants
Autonomous System (AS)
- A group of one or more IP prefixes (lists of IP addresses accessible on a network) run by one or more network operators that maintain a single, clearly defined routing policy.
- Generally a different network
Broadcast Storm
Result of an excessive amount of broadcast or multicast traffic on a computer network
Discovery Protocol
- Gather detailed information (IP, system version, and device information) from supporting devices directly.
- Simple network management protocol (SNMP)
- Link layer discovery protocol (LLDP)
- ping.
List Distance Vector Protocols
- RIP (Routing Information Protocol)
- BGP (Border Gateway Protocol)
- EIGRP (Enhanced Interiror Gateway Routing Protocol)
List Link State Protocols
- Open Shortest Path First (OSPF)
- Intermediate System to Intermediate System (IS-IS)
Routing Redundancy Protocl
Prevents disruptions in communication by automatically rerouting data traffic in cas of a path or device failure.
FHRP (First Hop Redundancy Protocol)
Provide automatic failover to a backup router to maintain uninterrupted network service
Subinterface
- Allows a single physical interface on a router or switch to be subdivided into multip logical interfaces
- Cost-efficient
- Conduct traffic management
GLBP (Gateway Load Balancing Protocol)
- Cisco Developed
- Adds load balanacing
- All routers active simultaneously
- Establish a fault-tolerant default gateway
- Presents as a asingle router
PIM (Protocol Independant Multicast)
Routes multicast traffic between routers and forms a multicast distribution tree
GRE (Generic Routing Encapsulation)
- Tunneling protocol
- Encaspulates a wide variety of L3 protocols
- Virtural point to point links over an Internet Protocol network
- Useful when connection similar network topologies over a different intermediate network
