Configuring and Troubleshooting Routers Flashcards
Routing Table
- Stores information of other IP networks and hosts in router
Routing Entry
Contains:
- Protocol: Source of the route
- Destination: Can be defined by specific host but is usually directed to network ID
- Interface: Local interface to use to forward a packet along the chosen route. Might be IP address of interface or layer 2 interface ID
- Gateway/next hop: IP Address of next router along path to destination
Direct Network Route
Category of routing table entry
- For subnets to which router is directly attached
Remote Network Routes
Category of routing table entry
- For subnets and IP networks that are not directly attached
Host Routes
Category of routing table entry
- For routes to a specific IP address.
- Has /32 network prefix
Default Routes
Category of routing table entry
- Used when an exact match for a network or host route is not found
- Most end systems are configured with default route pointing to default gateway
- Also sometime the simplest way for an edge router to forward to ISP router
Directly Connected Routes
- IP network or subnet for each active router interface is automatically added to routing table
Static Route
- Manually added
- Only changes if edited by administrator
- Can be set tp be persistent or non-persistent (removed from table at reboot)
Hop Count
- Each router along path counts as one hop
- Switches do not count as hops
TTL
Time to Live
- At each router, TTL IP header field is decreased by 1.
- Could be greater if router is congested
- Nominally the number of seconds a packet can stay on network before being discarded
- In practice, it is maximum hop count
- At 0 packet is discarded
- Prevents badly addressed packets from permanently staying on network
Dynamic Routing
- Protocol that uses algorithms and metrics to build routing information
- Stores information about the networks to which the router is connected
- Prioritizes paths
Distance Vector
- Algorithm used by routing protocols that select a forwarding path based on next hop router and lowest hop count to destination network
Convergence
- Process whereby routers running dynamic routing algorithms agree on network topology
- Important to adapt to changes in network topology
- Network where all routers share same topology is call steady state
AS
Autonomous System
- network under administrative control of single owner
IGP
Interior Gateway Protocol
- Identifies routes within AS (Autonomous System)
EGP
Exterior Gateway Protocol
- Advertises routes between autonomous systems
- Includes a field to communicate the networks autonomous system ID
- Allows network owners to determine if they can use paths through other orgs network
RIP
Routing Information Protocol
Type: Distance Vector
Class: IGP
Transport: UDP (Port 520 or 521)
- Maximum hop count 15, limits size of network
- Best suited for small networks with limited failover routes
EIGRP
Enhanced Gateway Routing Protocol
Type: Distance Vector/Hybrid
Class: IGP
Transport: Native (Port 88)
- Used Bandwidth and Delay for metric
- Only sends routing information upon topology change
- Faster convergence
- Maximum hops of 255
- Not encapsulated in TCP or UDP
OSPF
Open Shortest Path First
Type: Link State
Class: IGP
Transport: Native IP (89)
- Stores complete network topology to asses least cost paths
- Best suited for large orgs with multiple redundant paths
- Makes small, frequent updates for rapid convergence
- Require more CPU and memory
BGP
Border Gateway Protocol
Type: Path Vector
Class: EGP
Transport: TCP (Port 179)
- Primarily used on the internet, between ISPs
- Based multiple metrics like hop count, weight preference, origin and community
- Prioritizez stability and can be slow to converge
Longest Prefix Match
- Determining factor if router has similar networks in its routing table
- Routes base on longest prefix
AD
Administrative Distance - Used to express relative trustworthiness of protocol supplying route to routers - Used to break ties in prefix length and provide backup routes - By default they are: Local interface: 0 Static route: 1 BGP: 20 EIGRP: 90 OSPF: 110 RIP: 120 Unknown: 255
CIDR
Classless Inter-Domain Routing
- Uses bits normally assigned to network ID to mask complexity of subnet and host addressing
- Also know as supernetting
Link State
- Algorithm that allows router to store complete network topology
- Assesses least-cost paths based on this information
